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0001 /*
0002  *  linux/fs/namespace.c
0003  *
0004  * (C) Copyright Al Viro 2000, 2001
0005  *  Released under GPL v2.
0006  *
0007  * Based on code from fs/super.c, copyright Linus Torvalds and others.
0008  * Heavily rewritten.
0009  */
0010 
0011 #include <linux/syscalls.h>
0012 #include <linux/export.h>
0013 #include <linux/capability.h>
0014 #include <linux/mnt_namespace.h>
0015 #include <linux/user_namespace.h>
0016 #include <linux/namei.h>
0017 #include <linux/security.h>
0018 #include <linux/idr.h>
0019 #include <linux/init.h>     /* init_rootfs */
0020 #include <linux/fs_struct.h>    /* get_fs_root et.al. */
0021 #include <linux/fsnotify.h> /* fsnotify_vfsmount_delete */
0022 #include <linux/uaccess.h>
0023 #include <linux/proc_ns.h>
0024 #include <linux/magic.h>
0025 #include <linux/bootmem.h>
0026 #include <linux/task_work.h>
0027 #include "pnode.h"
0028 #include "internal.h"
0029 
0030 /* Maximum number of mounts in a mount namespace */
0031 unsigned int sysctl_mount_max __read_mostly = 100000;
0032 
0033 static unsigned int m_hash_mask __read_mostly;
0034 static unsigned int m_hash_shift __read_mostly;
0035 static unsigned int mp_hash_mask __read_mostly;
0036 static unsigned int mp_hash_shift __read_mostly;
0037 
0038 static __initdata unsigned long mhash_entries;
0039 static int __init set_mhash_entries(char *str)
0040 {
0041     if (!str)
0042         return 0;
0043     mhash_entries = simple_strtoul(str, &str, 0);
0044     return 1;
0045 }
0046 __setup("mhash_entries=", set_mhash_entries);
0047 
0048 static __initdata unsigned long mphash_entries;
0049 static int __init set_mphash_entries(char *str)
0050 {
0051     if (!str)
0052         return 0;
0053     mphash_entries = simple_strtoul(str, &str, 0);
0054     return 1;
0055 }
0056 __setup("mphash_entries=", set_mphash_entries);
0057 
0058 static u64 event;
0059 static DEFINE_IDA(mnt_id_ida);
0060 static DEFINE_IDA(mnt_group_ida);
0061 static DEFINE_SPINLOCK(mnt_id_lock);
0062 static int mnt_id_start = 0;
0063 static int mnt_group_start = 1;
0064 
0065 static struct hlist_head *mount_hashtable __read_mostly;
0066 static struct hlist_head *mountpoint_hashtable __read_mostly;
0067 static struct kmem_cache *mnt_cache __read_mostly;
0068 static DECLARE_RWSEM(namespace_sem);
0069 
0070 /* /sys/fs */
0071 struct kobject *fs_kobj;
0072 EXPORT_SYMBOL_GPL(fs_kobj);
0073 
0074 /*
0075  * vfsmount lock may be taken for read to prevent changes to the
0076  * vfsmount hash, ie. during mountpoint lookups or walking back
0077  * up the tree.
0078  *
0079  * It should be taken for write in all cases where the vfsmount
0080  * tree or hash is modified or when a vfsmount structure is modified.
0081  */
0082 __cacheline_aligned_in_smp DEFINE_SEQLOCK(mount_lock);
0083 
0084 static inline struct hlist_head *m_hash(struct vfsmount *mnt, struct dentry *dentry)
0085 {
0086     unsigned long tmp = ((unsigned long)mnt / L1_CACHE_BYTES);
0087     tmp += ((unsigned long)dentry / L1_CACHE_BYTES);
0088     tmp = tmp + (tmp >> m_hash_shift);
0089     return &mount_hashtable[tmp & m_hash_mask];
0090 }
0091 
0092 static inline struct hlist_head *mp_hash(struct dentry *dentry)
0093 {
0094     unsigned long tmp = ((unsigned long)dentry / L1_CACHE_BYTES);
0095     tmp = tmp + (tmp >> mp_hash_shift);
0096     return &mountpoint_hashtable[tmp & mp_hash_mask];
0097 }
0098 
0099 static int mnt_alloc_id(struct mount *mnt)
0100 {
0101     int res;
0102 
0103 retry:
0104     ida_pre_get(&mnt_id_ida, GFP_KERNEL);
0105     spin_lock(&mnt_id_lock);
0106     res = ida_get_new_above(&mnt_id_ida, mnt_id_start, &mnt->mnt_id);
0107     if (!res)
0108         mnt_id_start = mnt->mnt_id + 1;
0109     spin_unlock(&mnt_id_lock);
0110     if (res == -EAGAIN)
0111         goto retry;
0112 
0113     return res;
0114 }
0115 
0116 static void mnt_free_id(struct mount *mnt)
0117 {
0118     int id = mnt->mnt_id;
0119     spin_lock(&mnt_id_lock);
0120     ida_remove(&mnt_id_ida, id);
0121     if (mnt_id_start > id)
0122         mnt_id_start = id;
0123     spin_unlock(&mnt_id_lock);
0124 }
0125 
0126 /*
0127  * Allocate a new peer group ID
0128  *
0129  * mnt_group_ida is protected by namespace_sem
0130  */
0131 static int mnt_alloc_group_id(struct mount *mnt)
0132 {
0133     int res;
0134 
0135     if (!ida_pre_get(&mnt_group_ida, GFP_KERNEL))
0136         return -ENOMEM;
0137 
0138     res = ida_get_new_above(&mnt_group_ida,
0139                 mnt_group_start,
0140                 &mnt->mnt_group_id);
0141     if (!res)
0142         mnt_group_start = mnt->mnt_group_id + 1;
0143 
0144     return res;
0145 }
0146 
0147 /*
0148  * Release a peer group ID
0149  */
0150 void mnt_release_group_id(struct mount *mnt)
0151 {
0152     int id = mnt->mnt_group_id;
0153     ida_remove(&mnt_group_ida, id);
0154     if (mnt_group_start > id)
0155         mnt_group_start = id;
0156     mnt->mnt_group_id = 0;
0157 }
0158 
0159 /*
0160  * vfsmount lock must be held for read
0161  */
0162 static inline void mnt_add_count(struct mount *mnt, int n)
0163 {
0164 #ifdef CONFIG_SMP
0165     this_cpu_add(mnt->mnt_pcp->mnt_count, n);
0166 #else
0167     preempt_disable();
0168     mnt->mnt_count += n;
0169     preempt_enable();
0170 #endif
0171 }
0172 
0173 /*
0174  * vfsmount lock must be held for write
0175  */
0176 unsigned int mnt_get_count(struct mount *mnt)
0177 {
0178 #ifdef CONFIG_SMP
0179     unsigned int count = 0;
0180     int cpu;
0181 
0182     for_each_possible_cpu(cpu) {
0183         count += per_cpu_ptr(mnt->mnt_pcp, cpu)->mnt_count;
0184     }
0185 
0186     return count;
0187 #else
0188     return mnt->mnt_count;
0189 #endif
0190 }
0191 
0192 static void drop_mountpoint(struct fs_pin *p)
0193 {
0194     struct mount *m = container_of(p, struct mount, mnt_umount);
0195     dput(m->mnt_ex_mountpoint);
0196     pin_remove(p);
0197     mntput(&m->mnt);
0198 }
0199 
0200 static struct mount *alloc_vfsmnt(const char *name)
0201 {
0202     struct mount *mnt = kmem_cache_zalloc(mnt_cache, GFP_KERNEL);
0203     if (mnt) {
0204         int err;
0205 
0206         err = mnt_alloc_id(mnt);
0207         if (err)
0208             goto out_free_cache;
0209 
0210         if (name) {
0211             mnt->mnt_devname = kstrdup_const(name, GFP_KERNEL);
0212             if (!mnt->mnt_devname)
0213                 goto out_free_id;
0214         }
0215 
0216 #ifdef CONFIG_SMP
0217         mnt->mnt_pcp = alloc_percpu(struct mnt_pcp);
0218         if (!mnt->mnt_pcp)
0219             goto out_free_devname;
0220 
0221         this_cpu_add(mnt->mnt_pcp->mnt_count, 1);
0222 #else
0223         mnt->mnt_count = 1;
0224         mnt->mnt_writers = 0;
0225 #endif
0226 
0227         INIT_HLIST_NODE(&mnt->mnt_hash);
0228         INIT_LIST_HEAD(&mnt->mnt_child);
0229         INIT_LIST_HEAD(&mnt->mnt_mounts);
0230         INIT_LIST_HEAD(&mnt->mnt_list);
0231         INIT_LIST_HEAD(&mnt->mnt_expire);
0232         INIT_LIST_HEAD(&mnt->mnt_share);
0233         INIT_LIST_HEAD(&mnt->mnt_slave_list);
0234         INIT_LIST_HEAD(&mnt->mnt_slave);
0235         INIT_HLIST_NODE(&mnt->mnt_mp_list);
0236 #ifdef CONFIG_FSNOTIFY
0237         INIT_HLIST_HEAD(&mnt->mnt_fsnotify_marks);
0238 #endif
0239         init_fs_pin(&mnt->mnt_umount, drop_mountpoint);
0240     }
0241     return mnt;
0242 
0243 #ifdef CONFIG_SMP
0244 out_free_devname:
0245     kfree_const(mnt->mnt_devname);
0246 #endif
0247 out_free_id:
0248     mnt_free_id(mnt);
0249 out_free_cache:
0250     kmem_cache_free(mnt_cache, mnt);
0251     return NULL;
0252 }
0253 
0254 /*
0255  * Most r/o checks on a fs are for operations that take
0256  * discrete amounts of time, like a write() or unlink().
0257  * We must keep track of when those operations start
0258  * (for permission checks) and when they end, so that
0259  * we can determine when writes are able to occur to
0260  * a filesystem.
0261  */
0262 /*
0263  * __mnt_is_readonly: check whether a mount is read-only
0264  * @mnt: the mount to check for its write status
0265  *
0266  * This shouldn't be used directly ouside of the VFS.
0267  * It does not guarantee that the filesystem will stay
0268  * r/w, just that it is right *now*.  This can not and
0269  * should not be used in place of IS_RDONLY(inode).
0270  * mnt_want/drop_write() will _keep_ the filesystem
0271  * r/w.
0272  */
0273 int __mnt_is_readonly(struct vfsmount *mnt)
0274 {
0275     if (mnt->mnt_flags & MNT_READONLY)
0276         return 1;
0277     if (mnt->mnt_sb->s_flags & MS_RDONLY)
0278         return 1;
0279     return 0;
0280 }
0281 EXPORT_SYMBOL_GPL(__mnt_is_readonly);
0282 
0283 static inline void mnt_inc_writers(struct mount *mnt)
0284 {
0285 #ifdef CONFIG_SMP
0286     this_cpu_inc(mnt->mnt_pcp->mnt_writers);
0287 #else
0288     mnt->mnt_writers++;
0289 #endif
0290 }
0291 
0292 static inline void mnt_dec_writers(struct mount *mnt)
0293 {
0294 #ifdef CONFIG_SMP
0295     this_cpu_dec(mnt->mnt_pcp->mnt_writers);
0296 #else
0297     mnt->mnt_writers--;
0298 #endif
0299 }
0300 
0301 static unsigned int mnt_get_writers(struct mount *mnt)
0302 {
0303 #ifdef CONFIG_SMP
0304     unsigned int count = 0;
0305     int cpu;
0306 
0307     for_each_possible_cpu(cpu) {
0308         count += per_cpu_ptr(mnt->mnt_pcp, cpu)->mnt_writers;
0309     }
0310 
0311     return count;
0312 #else
0313     return mnt->mnt_writers;
0314 #endif
0315 }
0316 
0317 static int mnt_is_readonly(struct vfsmount *mnt)
0318 {
0319     if (mnt->mnt_sb->s_readonly_remount)
0320         return 1;
0321     /* Order wrt setting s_flags/s_readonly_remount in do_remount() */
0322     smp_rmb();
0323     return __mnt_is_readonly(mnt);
0324 }
0325 
0326 /*
0327  * Most r/o & frozen checks on a fs are for operations that take discrete
0328  * amounts of time, like a write() or unlink().  We must keep track of when
0329  * those operations start (for permission checks) and when they end, so that we
0330  * can determine when writes are able to occur to a filesystem.
0331  */
0332 /**
0333  * __mnt_want_write - get write access to a mount without freeze protection
0334  * @m: the mount on which to take a write
0335  *
0336  * This tells the low-level filesystem that a write is about to be performed to
0337  * it, and makes sure that writes are allowed (mnt it read-write) before
0338  * returning success. This operation does not protect against filesystem being
0339  * frozen. When the write operation is finished, __mnt_drop_write() must be
0340  * called. This is effectively a refcount.
0341  */
0342 int __mnt_want_write(struct vfsmount *m)
0343 {
0344     struct mount *mnt = real_mount(m);
0345     int ret = 0;
0346 
0347     preempt_disable();
0348     mnt_inc_writers(mnt);
0349     /*
0350      * The store to mnt_inc_writers must be visible before we pass
0351      * MNT_WRITE_HOLD loop below, so that the slowpath can see our
0352      * incremented count after it has set MNT_WRITE_HOLD.
0353      */
0354     smp_mb();
0355     while (ACCESS_ONCE(mnt->mnt.mnt_flags) & MNT_WRITE_HOLD)
0356         cpu_relax();
0357     /*
0358      * After the slowpath clears MNT_WRITE_HOLD, mnt_is_readonly will
0359      * be set to match its requirements. So we must not load that until
0360      * MNT_WRITE_HOLD is cleared.
0361      */
0362     smp_rmb();
0363     if (mnt_is_readonly(m)) {
0364         mnt_dec_writers(mnt);
0365         ret = -EROFS;
0366     }
0367     preempt_enable();
0368 
0369     return ret;
0370 }
0371 
0372 /**
0373  * mnt_want_write - get write access to a mount
0374  * @m: the mount on which to take a write
0375  *
0376  * This tells the low-level filesystem that a write is about to be performed to
0377  * it, and makes sure that writes are allowed (mount is read-write, filesystem
0378  * is not frozen) before returning success.  When the write operation is
0379  * finished, mnt_drop_write() must be called.  This is effectively a refcount.
0380  */
0381 int mnt_want_write(struct vfsmount *m)
0382 {
0383     int ret;
0384 
0385     sb_start_write(m->mnt_sb);
0386     ret = __mnt_want_write(m);
0387     if (ret)
0388         sb_end_write(m->mnt_sb);
0389     return ret;
0390 }
0391 EXPORT_SYMBOL_GPL(mnt_want_write);
0392 
0393 /**
0394  * mnt_clone_write - get write access to a mount
0395  * @mnt: the mount on which to take a write
0396  *
0397  * This is effectively like mnt_want_write, except
0398  * it must only be used to take an extra write reference
0399  * on a mountpoint that we already know has a write reference
0400  * on it. This allows some optimisation.
0401  *
0402  * After finished, mnt_drop_write must be called as usual to
0403  * drop the reference.
0404  */
0405 int mnt_clone_write(struct vfsmount *mnt)
0406 {
0407     /* superblock may be r/o */
0408     if (__mnt_is_readonly(mnt))
0409         return -EROFS;
0410     preempt_disable();
0411     mnt_inc_writers(real_mount(mnt));
0412     preempt_enable();
0413     return 0;
0414 }
0415 EXPORT_SYMBOL_GPL(mnt_clone_write);
0416 
0417 /**
0418  * __mnt_want_write_file - get write access to a file's mount
0419  * @file: the file who's mount on which to take a write
0420  *
0421  * This is like __mnt_want_write, but it takes a file and can
0422  * do some optimisations if the file is open for write already
0423  */
0424 int __mnt_want_write_file(struct file *file)
0425 {
0426     if (!(file->f_mode & FMODE_WRITER))
0427         return __mnt_want_write(file->f_path.mnt);
0428     else
0429         return mnt_clone_write(file->f_path.mnt);
0430 }
0431 
0432 /**
0433  * mnt_want_write_file - get write access to a file's mount
0434  * @file: the file who's mount on which to take a write
0435  *
0436  * This is like mnt_want_write, but it takes a file and can
0437  * do some optimisations if the file is open for write already
0438  */
0439 int mnt_want_write_file(struct file *file)
0440 {
0441     int ret;
0442 
0443     sb_start_write(file->f_path.mnt->mnt_sb);
0444     ret = __mnt_want_write_file(file);
0445     if (ret)
0446         sb_end_write(file->f_path.mnt->mnt_sb);
0447     return ret;
0448 }
0449 EXPORT_SYMBOL_GPL(mnt_want_write_file);
0450 
0451 /**
0452  * __mnt_drop_write - give up write access to a mount
0453  * @mnt: the mount on which to give up write access
0454  *
0455  * Tells the low-level filesystem that we are done
0456  * performing writes to it.  Must be matched with
0457  * __mnt_want_write() call above.
0458  */
0459 void __mnt_drop_write(struct vfsmount *mnt)
0460 {
0461     preempt_disable();
0462     mnt_dec_writers(real_mount(mnt));
0463     preempt_enable();
0464 }
0465 
0466 /**
0467  * mnt_drop_write - give up write access to a mount
0468  * @mnt: the mount on which to give up write access
0469  *
0470  * Tells the low-level filesystem that we are done performing writes to it and
0471  * also allows filesystem to be frozen again.  Must be matched with
0472  * mnt_want_write() call above.
0473  */
0474 void mnt_drop_write(struct vfsmount *mnt)
0475 {
0476     __mnt_drop_write(mnt);
0477     sb_end_write(mnt->mnt_sb);
0478 }
0479 EXPORT_SYMBOL_GPL(mnt_drop_write);
0480 
0481 void __mnt_drop_write_file(struct file *file)
0482 {
0483     __mnt_drop_write(file->f_path.mnt);
0484 }
0485 
0486 void mnt_drop_write_file(struct file *file)
0487 {
0488     mnt_drop_write(file->f_path.mnt);
0489 }
0490 EXPORT_SYMBOL(mnt_drop_write_file);
0491 
0492 static int mnt_make_readonly(struct mount *mnt)
0493 {
0494     int ret = 0;
0495 
0496     lock_mount_hash();
0497     mnt->mnt.mnt_flags |= MNT_WRITE_HOLD;
0498     /*
0499      * After storing MNT_WRITE_HOLD, we'll read the counters. This store
0500      * should be visible before we do.
0501      */
0502     smp_mb();
0503 
0504     /*
0505      * With writers on hold, if this value is zero, then there are
0506      * definitely no active writers (although held writers may subsequently
0507      * increment the count, they'll have to wait, and decrement it after
0508      * seeing MNT_READONLY).
0509      *
0510      * It is OK to have counter incremented on one CPU and decremented on
0511      * another: the sum will add up correctly. The danger would be when we
0512      * sum up each counter, if we read a counter before it is incremented,
0513      * but then read another CPU's count which it has been subsequently
0514      * decremented from -- we would see more decrements than we should.
0515      * MNT_WRITE_HOLD protects against this scenario, because
0516      * mnt_want_write first increments count, then smp_mb, then spins on
0517      * MNT_WRITE_HOLD, so it can't be decremented by another CPU while
0518      * we're counting up here.
0519      */
0520     if (mnt_get_writers(mnt) > 0)
0521         ret = -EBUSY;
0522     else
0523         mnt->mnt.mnt_flags |= MNT_READONLY;
0524     /*
0525      * MNT_READONLY must become visible before ~MNT_WRITE_HOLD, so writers
0526      * that become unheld will see MNT_READONLY.
0527      */
0528     smp_wmb();
0529     mnt->mnt.mnt_flags &= ~MNT_WRITE_HOLD;
0530     unlock_mount_hash();
0531     return ret;
0532 }
0533 
0534 static void __mnt_unmake_readonly(struct mount *mnt)
0535 {
0536     lock_mount_hash();
0537     mnt->mnt.mnt_flags &= ~MNT_READONLY;
0538     unlock_mount_hash();
0539 }
0540 
0541 int sb_prepare_remount_readonly(struct super_block *sb)
0542 {
0543     struct mount *mnt;
0544     int err = 0;
0545 
0546     /* Racy optimization.  Recheck the counter under MNT_WRITE_HOLD */
0547     if (atomic_long_read(&sb->s_remove_count))
0548         return -EBUSY;
0549 
0550     lock_mount_hash();
0551     list_for_each_entry(mnt, &sb->s_mounts, mnt_instance) {
0552         if (!(mnt->mnt.mnt_flags & MNT_READONLY)) {
0553             mnt->mnt.mnt_flags |= MNT_WRITE_HOLD;
0554             smp_mb();
0555             if (mnt_get_writers(mnt) > 0) {
0556                 err = -EBUSY;
0557                 break;
0558             }
0559         }
0560     }
0561     if (!err && atomic_long_read(&sb->s_remove_count))
0562         err = -EBUSY;
0563 
0564     if (!err) {
0565         sb->s_readonly_remount = 1;
0566         smp_wmb();
0567     }
0568     list_for_each_entry(mnt, &sb->s_mounts, mnt_instance) {
0569         if (mnt->mnt.mnt_flags & MNT_WRITE_HOLD)
0570             mnt->mnt.mnt_flags &= ~MNT_WRITE_HOLD;
0571     }
0572     unlock_mount_hash();
0573 
0574     return err;
0575 }
0576 
0577 static void free_vfsmnt(struct mount *mnt)
0578 {
0579     kfree_const(mnt->mnt_devname);
0580 #ifdef CONFIG_SMP
0581     free_percpu(mnt->mnt_pcp);
0582 #endif
0583     kmem_cache_free(mnt_cache, mnt);
0584 }
0585 
0586 static void delayed_free_vfsmnt(struct rcu_head *head)
0587 {
0588     free_vfsmnt(container_of(head, struct mount, mnt_rcu));
0589 }
0590 
0591 /* call under rcu_read_lock */
0592 int __legitimize_mnt(struct vfsmount *bastard, unsigned seq)
0593 {
0594     struct mount *mnt;
0595     if (read_seqretry(&mount_lock, seq))
0596         return 1;
0597     if (bastard == NULL)
0598         return 0;
0599     mnt = real_mount(bastard);
0600     mnt_add_count(mnt, 1);
0601     if (likely(!read_seqretry(&mount_lock, seq)))
0602         return 0;
0603     if (bastard->mnt_flags & MNT_SYNC_UMOUNT) {
0604         mnt_add_count(mnt, -1);
0605         return 1;
0606     }
0607     return -1;
0608 }
0609 
0610 /* call under rcu_read_lock */
0611 bool legitimize_mnt(struct vfsmount *bastard, unsigned seq)
0612 {
0613     int res = __legitimize_mnt(bastard, seq);
0614     if (likely(!res))
0615         return true;
0616     if (unlikely(res < 0)) {
0617         rcu_read_unlock();
0618         mntput(bastard);
0619         rcu_read_lock();
0620     }
0621     return false;
0622 }
0623 
0624 /*
0625  * find the first mount at @dentry on vfsmount @mnt.
0626  * call under rcu_read_lock()
0627  */
0628 struct mount *__lookup_mnt(struct vfsmount *mnt, struct dentry *dentry)
0629 {
0630     struct hlist_head *head = m_hash(mnt, dentry);
0631     struct mount *p;
0632 
0633     hlist_for_each_entry_rcu(p, head, mnt_hash)
0634         if (&p->mnt_parent->mnt == mnt && p->mnt_mountpoint == dentry)
0635             return p;
0636     return NULL;
0637 }
0638 
0639 /*
0640  * find the last mount at @dentry on vfsmount @mnt.
0641  * mount_lock must be held.
0642  */
0643 struct mount *__lookup_mnt_last(struct vfsmount *mnt, struct dentry *dentry)
0644 {
0645     struct mount *p, *res = NULL;
0646     p = __lookup_mnt(mnt, dentry);
0647     if (!p)
0648         goto out;
0649     if (!(p->mnt.mnt_flags & MNT_UMOUNT))
0650         res = p;
0651     hlist_for_each_entry_continue(p, mnt_hash) {
0652         if (&p->mnt_parent->mnt != mnt || p->mnt_mountpoint != dentry)
0653             break;
0654         if (!(p->mnt.mnt_flags & MNT_UMOUNT))
0655             res = p;
0656     }
0657 out:
0658     return res;
0659 }
0660 
0661 /*
0662  * lookup_mnt - Return the first child mount mounted at path
0663  *
0664  * "First" means first mounted chronologically.  If you create the
0665  * following mounts:
0666  *
0667  * mount /dev/sda1 /mnt
0668  * mount /dev/sda2 /mnt
0669  * mount /dev/sda3 /mnt
0670  *
0671  * Then lookup_mnt() on the base /mnt dentry in the root mount will
0672  * return successively the root dentry and vfsmount of /dev/sda1, then
0673  * /dev/sda2, then /dev/sda3, then NULL.
0674  *
0675  * lookup_mnt takes a reference to the found vfsmount.
0676  */
0677 struct vfsmount *lookup_mnt(const struct path *path)
0678 {
0679     struct mount *child_mnt;
0680     struct vfsmount *m;
0681     unsigned seq;
0682 
0683     rcu_read_lock();
0684     do {
0685         seq = read_seqbegin(&mount_lock);
0686         child_mnt = __lookup_mnt(path->mnt, path->dentry);
0687         m = child_mnt ? &child_mnt->mnt : NULL;
0688     } while (!legitimize_mnt(m, seq));
0689     rcu_read_unlock();
0690     return m;
0691 }
0692 
0693 /*
0694  * __is_local_mountpoint - Test to see if dentry is a mountpoint in the
0695  *                         current mount namespace.
0696  *
0697  * The common case is dentries are not mountpoints at all and that
0698  * test is handled inline.  For the slow case when we are actually
0699  * dealing with a mountpoint of some kind, walk through all of the
0700  * mounts in the current mount namespace and test to see if the dentry
0701  * is a mountpoint.
0702  *
0703  * The mount_hashtable is not usable in the context because we
0704  * need to identify all mounts that may be in the current mount
0705  * namespace not just a mount that happens to have some specified
0706  * parent mount.
0707  */
0708 bool __is_local_mountpoint(struct dentry *dentry)
0709 {
0710     struct mnt_namespace *ns = current->nsproxy->mnt_ns;
0711     struct mount *mnt;
0712     bool is_covered = false;
0713 
0714     if (!d_mountpoint(dentry))
0715         goto out;
0716 
0717     down_read(&namespace_sem);
0718     list_for_each_entry(mnt, &ns->list, mnt_list) {
0719         is_covered = (mnt->mnt_mountpoint == dentry);
0720         if (is_covered)
0721             break;
0722     }
0723     up_read(&namespace_sem);
0724 out:
0725     return is_covered;
0726 }
0727 
0728 static struct mountpoint *lookup_mountpoint(struct dentry *dentry)
0729 {
0730     struct hlist_head *chain = mp_hash(dentry);
0731     struct mountpoint *mp;
0732 
0733     hlist_for_each_entry(mp, chain, m_hash) {
0734         if (mp->m_dentry == dentry) {
0735             /* might be worth a WARN_ON() */
0736             if (d_unlinked(dentry))
0737                 return ERR_PTR(-ENOENT);
0738             mp->m_count++;
0739             return mp;
0740         }
0741     }
0742     return NULL;
0743 }
0744 
0745 static struct mountpoint *get_mountpoint(struct dentry *dentry)
0746 {
0747     struct mountpoint *mp, *new = NULL;
0748     int ret;
0749 
0750     if (d_mountpoint(dentry)) {
0751 mountpoint:
0752         read_seqlock_excl(&mount_lock);
0753         mp = lookup_mountpoint(dentry);
0754         read_sequnlock_excl(&mount_lock);
0755         if (mp)
0756             goto done;
0757     }
0758 
0759     if (!new)
0760         new = kmalloc(sizeof(struct mountpoint), GFP_KERNEL);
0761     if (!new)
0762         return ERR_PTR(-ENOMEM);
0763 
0764 
0765     /* Exactly one processes may set d_mounted */
0766     ret = d_set_mounted(dentry);
0767 
0768     /* Someone else set d_mounted? */
0769     if (ret == -EBUSY)
0770         goto mountpoint;
0771 
0772     /* The dentry is not available as a mountpoint? */
0773     mp = ERR_PTR(ret);
0774     if (ret)
0775         goto done;
0776 
0777     /* Add the new mountpoint to the hash table */
0778     read_seqlock_excl(&mount_lock);
0779     new->m_dentry = dentry;
0780     new->m_count = 1;
0781     hlist_add_head(&new->m_hash, mp_hash(dentry));
0782     INIT_HLIST_HEAD(&new->m_list);
0783     read_sequnlock_excl(&mount_lock);
0784 
0785     mp = new;
0786     new = NULL;
0787 done:
0788     kfree(new);
0789     return mp;
0790 }
0791 
0792 static void put_mountpoint(struct mountpoint *mp)
0793 {
0794     if (!--mp->m_count) {
0795         struct dentry *dentry = mp->m_dentry;
0796         BUG_ON(!hlist_empty(&mp->m_list));
0797         spin_lock(&dentry->d_lock);
0798         dentry->d_flags &= ~DCACHE_MOUNTED;
0799         spin_unlock(&dentry->d_lock);
0800         hlist_del(&mp->m_hash);
0801         kfree(mp);
0802     }
0803 }
0804 
0805 static inline int check_mnt(struct mount *mnt)
0806 {
0807     return mnt->mnt_ns == current->nsproxy->mnt_ns;
0808 }
0809 
0810 /*
0811  * vfsmount lock must be held for write
0812  */
0813 static void touch_mnt_namespace(struct mnt_namespace *ns)
0814 {
0815     if (ns) {
0816         ns->event = ++event;
0817         wake_up_interruptible(&ns->poll);
0818     }
0819 }
0820 
0821 /*
0822  * vfsmount lock must be held for write
0823  */
0824 static void __touch_mnt_namespace(struct mnt_namespace *ns)
0825 {
0826     if (ns && ns->event != event) {
0827         ns->event = event;
0828         wake_up_interruptible(&ns->poll);
0829     }
0830 }
0831 
0832 /*
0833  * vfsmount lock must be held for write
0834  */
0835 static void unhash_mnt(struct mount *mnt)
0836 {
0837     mnt->mnt_parent = mnt;
0838     mnt->mnt_mountpoint = mnt->mnt.mnt_root;
0839     list_del_init(&mnt->mnt_child);
0840     hlist_del_init_rcu(&mnt->mnt_hash);
0841     hlist_del_init(&mnt->mnt_mp_list);
0842     put_mountpoint(mnt->mnt_mp);
0843     mnt->mnt_mp = NULL;
0844 }
0845 
0846 /*
0847  * vfsmount lock must be held for write
0848  */
0849 static void detach_mnt(struct mount *mnt, struct path *old_path)
0850 {
0851     old_path->dentry = mnt->mnt_mountpoint;
0852     old_path->mnt = &mnt->mnt_parent->mnt;
0853     unhash_mnt(mnt);
0854 }
0855 
0856 /*
0857  * vfsmount lock must be held for write
0858  */
0859 static void umount_mnt(struct mount *mnt)
0860 {
0861     /* old mountpoint will be dropped when we can do that */
0862     mnt->mnt_ex_mountpoint = mnt->mnt_mountpoint;
0863     unhash_mnt(mnt);
0864 }
0865 
0866 /*
0867  * vfsmount lock must be held for write
0868  */
0869 void mnt_set_mountpoint(struct mount *mnt,
0870             struct mountpoint *mp,
0871             struct mount *child_mnt)
0872 {
0873     mp->m_count++;
0874     mnt_add_count(mnt, 1);  /* essentially, that's mntget */
0875     child_mnt->mnt_mountpoint = dget(mp->m_dentry);
0876     child_mnt->mnt_parent = mnt;
0877     child_mnt->mnt_mp = mp;
0878     hlist_add_head(&child_mnt->mnt_mp_list, &mp->m_list);
0879 }
0880 
0881 /*
0882  * vfsmount lock must be held for write
0883  */
0884 static void attach_mnt(struct mount *mnt,
0885             struct mount *parent,
0886             struct mountpoint *mp)
0887 {
0888     mnt_set_mountpoint(parent, mp, mnt);
0889     hlist_add_head_rcu(&mnt->mnt_hash, m_hash(&parent->mnt, mp->m_dentry));
0890     list_add_tail(&mnt->mnt_child, &parent->mnt_mounts);
0891 }
0892 
0893 static void attach_shadowed(struct mount *mnt,
0894             struct mount *parent,
0895             struct mount *shadows)
0896 {
0897     if (shadows) {
0898         hlist_add_behind_rcu(&mnt->mnt_hash, &shadows->mnt_hash);
0899         list_add(&mnt->mnt_child, &shadows->mnt_child);
0900     } else {
0901         hlist_add_head_rcu(&mnt->mnt_hash,
0902                 m_hash(&parent->mnt, mnt->mnt_mountpoint));
0903         list_add_tail(&mnt->mnt_child, &parent->mnt_mounts);
0904     }
0905 }
0906 
0907 /*
0908  * vfsmount lock must be held for write
0909  */
0910 static void commit_tree(struct mount *mnt, struct mount *shadows)
0911 {
0912     struct mount *parent = mnt->mnt_parent;
0913     struct mount *m;
0914     LIST_HEAD(head);
0915     struct mnt_namespace *n = parent->mnt_ns;
0916 
0917     BUG_ON(parent == mnt);
0918 
0919     list_add_tail(&head, &mnt->mnt_list);
0920     list_for_each_entry(m, &head, mnt_list)
0921         m->mnt_ns = n;
0922 
0923     list_splice(&head, n->list.prev);
0924 
0925     n->mounts += n->pending_mounts;
0926     n->pending_mounts = 0;
0927 
0928     attach_shadowed(mnt, parent, shadows);
0929     touch_mnt_namespace(n);
0930 }
0931 
0932 static struct mount *next_mnt(struct mount *p, struct mount *root)
0933 {
0934     struct list_head *next = p->mnt_mounts.next;
0935     if (next == &p->mnt_mounts) {
0936         while (1) {
0937             if (p == root)
0938                 return NULL;
0939             next = p->mnt_child.next;
0940             if (next != &p->mnt_parent->mnt_mounts)
0941                 break;
0942             p = p->mnt_parent;
0943         }
0944     }
0945     return list_entry(next, struct mount, mnt_child);
0946 }
0947 
0948 static struct mount *skip_mnt_tree(struct mount *p)
0949 {
0950     struct list_head *prev = p->mnt_mounts.prev;
0951     while (prev != &p->mnt_mounts) {
0952         p = list_entry(prev, struct mount, mnt_child);
0953         prev = p->mnt_mounts.prev;
0954     }
0955     return p;
0956 }
0957 
0958 struct vfsmount *
0959 vfs_kern_mount(struct file_system_type *type, int flags, const char *name, void *data)
0960 {
0961     struct mount *mnt;
0962     struct dentry *root;
0963 
0964     if (!type)
0965         return ERR_PTR(-ENODEV);
0966 
0967     mnt = alloc_vfsmnt(name);
0968     if (!mnt)
0969         return ERR_PTR(-ENOMEM);
0970 
0971     if (flags & MS_KERNMOUNT)
0972         mnt->mnt.mnt_flags = MNT_INTERNAL;
0973 
0974     root = mount_fs(type, flags, name, data);
0975     if (IS_ERR(root)) {
0976         mnt_free_id(mnt);
0977         free_vfsmnt(mnt);
0978         return ERR_CAST(root);
0979     }
0980 
0981     mnt->mnt.mnt_root = root;
0982     mnt->mnt.mnt_sb = root->d_sb;
0983     mnt->mnt_mountpoint = mnt->mnt.mnt_root;
0984     mnt->mnt_parent = mnt;
0985     lock_mount_hash();
0986     list_add_tail(&mnt->mnt_instance, &root->d_sb->s_mounts);
0987     unlock_mount_hash();
0988     return &mnt->mnt;
0989 }
0990 EXPORT_SYMBOL_GPL(vfs_kern_mount);
0991 
0992 static struct mount *clone_mnt(struct mount *old, struct dentry *root,
0993                     int flag)
0994 {
0995     struct super_block *sb = old->mnt.mnt_sb;
0996     struct mount *mnt;
0997     int err;
0998 
0999     mnt = alloc_vfsmnt(old->mnt_devname);
1000     if (!mnt)
1001         return ERR_PTR(-ENOMEM);
1002 
1003     if (flag & (CL_SLAVE | CL_PRIVATE | CL_SHARED_TO_SLAVE))
1004         mnt->mnt_group_id = 0; /* not a peer of original */
1005     else
1006         mnt->mnt_group_id = old->mnt_group_id;
1007 
1008     if ((flag & CL_MAKE_SHARED) && !mnt->mnt_group_id) {
1009         err = mnt_alloc_group_id(mnt);
1010         if (err)
1011             goto out_free;
1012     }
1013 
1014     mnt->mnt.mnt_flags = old->mnt.mnt_flags & ~(MNT_WRITE_HOLD|MNT_MARKED);
1015     /* Don't allow unprivileged users to change mount flags */
1016     if (flag & CL_UNPRIVILEGED) {
1017         mnt->mnt.mnt_flags |= MNT_LOCK_ATIME;
1018 
1019         if (mnt->mnt.mnt_flags & MNT_READONLY)
1020             mnt->mnt.mnt_flags |= MNT_LOCK_READONLY;
1021 
1022         if (mnt->mnt.mnt_flags & MNT_NODEV)
1023             mnt->mnt.mnt_flags |= MNT_LOCK_NODEV;
1024 
1025         if (mnt->mnt.mnt_flags & MNT_NOSUID)
1026             mnt->mnt.mnt_flags |= MNT_LOCK_NOSUID;
1027 
1028         if (mnt->mnt.mnt_flags & MNT_NOEXEC)
1029             mnt->mnt.mnt_flags |= MNT_LOCK_NOEXEC;
1030     }
1031 
1032     /* Don't allow unprivileged users to reveal what is under a mount */
1033     if ((flag & CL_UNPRIVILEGED) &&
1034         (!(flag & CL_EXPIRE) || list_empty(&old->mnt_expire)))
1035         mnt->mnt.mnt_flags |= MNT_LOCKED;
1036 
1037     atomic_inc(&sb->s_active);
1038     mnt->mnt.mnt_sb = sb;
1039     mnt->mnt.mnt_root = dget(root);
1040     mnt->mnt_mountpoint = mnt->mnt.mnt_root;
1041     mnt->mnt_parent = mnt;
1042     lock_mount_hash();
1043     list_add_tail(&mnt->mnt_instance, &sb->s_mounts);
1044     unlock_mount_hash();
1045 
1046     if ((flag & CL_SLAVE) ||
1047         ((flag & CL_SHARED_TO_SLAVE) && IS_MNT_SHARED(old))) {
1048         list_add(&mnt->mnt_slave, &old->mnt_slave_list);
1049         mnt->mnt_master = old;
1050         CLEAR_MNT_SHARED(mnt);
1051     } else if (!(flag & CL_PRIVATE)) {
1052         if ((flag & CL_MAKE_SHARED) || IS_MNT_SHARED(old))
1053             list_add(&mnt->mnt_share, &old->mnt_share);
1054         if (IS_MNT_SLAVE(old))
1055             list_add(&mnt->mnt_slave, &old->mnt_slave);
1056         mnt->mnt_master = old->mnt_master;
1057     } else {
1058         CLEAR_MNT_SHARED(mnt);
1059     }
1060     if (flag & CL_MAKE_SHARED)
1061         set_mnt_shared(mnt);
1062 
1063     /* stick the duplicate mount on the same expiry list
1064      * as the original if that was on one */
1065     if (flag & CL_EXPIRE) {
1066         if (!list_empty(&old->mnt_expire))
1067             list_add(&mnt->mnt_expire, &old->mnt_expire);
1068     }
1069 
1070     return mnt;
1071 
1072  out_free:
1073     mnt_free_id(mnt);
1074     free_vfsmnt(mnt);
1075     return ERR_PTR(err);
1076 }
1077 
1078 static void cleanup_mnt(struct mount *mnt)
1079 {
1080     /*
1081      * This probably indicates that somebody messed
1082      * up a mnt_want/drop_write() pair.  If this
1083      * happens, the filesystem was probably unable
1084      * to make r/w->r/o transitions.
1085      */
1086     /*
1087      * The locking used to deal with mnt_count decrement provides barriers,
1088      * so mnt_get_writers() below is safe.
1089      */
1090     WARN_ON(mnt_get_writers(mnt));
1091     if (unlikely(mnt->mnt_pins.first))
1092         mnt_pin_kill(mnt);
1093     fsnotify_vfsmount_delete(&mnt->mnt);
1094     dput(mnt->mnt.mnt_root);
1095     deactivate_super(mnt->mnt.mnt_sb);
1096     mnt_free_id(mnt);
1097     call_rcu(&mnt->mnt_rcu, delayed_free_vfsmnt);
1098 }
1099 
1100 static void __cleanup_mnt(struct rcu_head *head)
1101 {
1102     cleanup_mnt(container_of(head, struct mount, mnt_rcu));
1103 }
1104 
1105 static LLIST_HEAD(delayed_mntput_list);
1106 static void delayed_mntput(struct work_struct *unused)
1107 {
1108     struct llist_node *node = llist_del_all(&delayed_mntput_list);
1109     struct llist_node *next;
1110 
1111     for (; node; node = next) {
1112         next = llist_next(node);
1113         cleanup_mnt(llist_entry(node, struct mount, mnt_llist));
1114     }
1115 }
1116 static DECLARE_DELAYED_WORK(delayed_mntput_work, delayed_mntput);
1117 
1118 static void mntput_no_expire(struct mount *mnt)
1119 {
1120     rcu_read_lock();
1121     mnt_add_count(mnt, -1);
1122     if (likely(mnt->mnt_ns)) { /* shouldn't be the last one */
1123         rcu_read_unlock();
1124         return;
1125     }
1126     lock_mount_hash();
1127     if (mnt_get_count(mnt)) {
1128         rcu_read_unlock();
1129         unlock_mount_hash();
1130         return;
1131     }
1132     if (unlikely(mnt->mnt.mnt_flags & MNT_DOOMED)) {
1133         rcu_read_unlock();
1134         unlock_mount_hash();
1135         return;
1136     }
1137     mnt->mnt.mnt_flags |= MNT_DOOMED;
1138     rcu_read_unlock();
1139 
1140     list_del(&mnt->mnt_instance);
1141 
1142     if (unlikely(!list_empty(&mnt->mnt_mounts))) {
1143         struct mount *p, *tmp;
1144         list_for_each_entry_safe(p, tmp, &mnt->mnt_mounts,  mnt_child) {
1145             umount_mnt(p);
1146         }
1147     }
1148     unlock_mount_hash();
1149 
1150     if (likely(!(mnt->mnt.mnt_flags & MNT_INTERNAL))) {
1151         struct task_struct *task = current;
1152         if (likely(!(task->flags & PF_KTHREAD))) {
1153             init_task_work(&mnt->mnt_rcu, __cleanup_mnt);
1154             if (!task_work_add(task, &mnt->mnt_rcu, true))
1155                 return;
1156         }
1157         if (llist_add(&mnt->mnt_llist, &delayed_mntput_list))
1158             schedule_delayed_work(&delayed_mntput_work, 1);
1159         return;
1160     }
1161     cleanup_mnt(mnt);
1162 }
1163 
1164 void mntput(struct vfsmount *mnt)
1165 {
1166     if (mnt) {
1167         struct mount *m = real_mount(mnt);
1168         /* avoid cacheline pingpong, hope gcc doesn't get "smart" */
1169         if (unlikely(m->mnt_expiry_mark))
1170             m->mnt_expiry_mark = 0;
1171         mntput_no_expire(m);
1172     }
1173 }
1174 EXPORT_SYMBOL(mntput);
1175 
1176 struct vfsmount *mntget(struct vfsmount *mnt)
1177 {
1178     if (mnt)
1179         mnt_add_count(real_mount(mnt), 1);
1180     return mnt;
1181 }
1182 EXPORT_SYMBOL(mntget);
1183 
1184 /* path_is_mountpoint() - Check if path is a mount in the current
1185  *                          namespace.
1186  *
1187  *  d_mountpoint() can only be used reliably to establish if a dentry is
1188  *  not mounted in any namespace and that common case is handled inline.
1189  *  d_mountpoint() isn't aware of the possibility there may be multiple
1190  *  mounts using a given dentry in a different namespace. This function
1191  *  checks if the passed in path is a mountpoint rather than the dentry
1192  *  alone.
1193  */
1194 bool path_is_mountpoint(const struct path *path)
1195 {
1196     unsigned seq;
1197     bool res;
1198 
1199     if (!d_mountpoint(path->dentry))
1200         return false;
1201 
1202     rcu_read_lock();
1203     do {
1204         seq = read_seqbegin(&mount_lock);
1205         res = __path_is_mountpoint(path);
1206     } while (read_seqretry(&mount_lock, seq));
1207     rcu_read_unlock();
1208 
1209     return res;
1210 }
1211 EXPORT_SYMBOL(path_is_mountpoint);
1212 
1213 struct vfsmount *mnt_clone_internal(const struct path *path)
1214 {
1215     struct mount *p;
1216     p = clone_mnt(real_mount(path->mnt), path->dentry, CL_PRIVATE);
1217     if (IS_ERR(p))
1218         return ERR_CAST(p);
1219     p->mnt.mnt_flags |= MNT_INTERNAL;
1220     return &p->mnt;
1221 }
1222 
1223 static inline void mangle(struct seq_file *m, const char *s)
1224 {
1225     seq_escape(m, s, " \t\n\\");
1226 }
1227 
1228 /*
1229  * Simple .show_options callback for filesystems which don't want to
1230  * implement more complex mount option showing.
1231  *
1232  * See also save_mount_options().
1233  */
1234 int generic_show_options(struct seq_file *m, struct dentry *root)
1235 {
1236     const char *options;
1237 
1238     rcu_read_lock();
1239     options = rcu_dereference(root->d_sb->s_options);
1240 
1241     if (options != NULL && options[0]) {
1242         seq_putc(m, ',');
1243         mangle(m, options);
1244     }
1245     rcu_read_unlock();
1246 
1247     return 0;
1248 }
1249 EXPORT_SYMBOL(generic_show_options);
1250 
1251 /*
1252  * If filesystem uses generic_show_options(), this function should be
1253  * called from the fill_super() callback.
1254  *
1255  * The .remount_fs callback usually needs to be handled in a special
1256  * way, to make sure, that previous options are not overwritten if the
1257  * remount fails.
1258  *
1259  * Also note, that if the filesystem's .remount_fs function doesn't
1260  * reset all options to their default value, but changes only newly
1261  * given options, then the displayed options will not reflect reality
1262  * any more.
1263  */
1264 void save_mount_options(struct super_block *sb, char *options)
1265 {
1266     BUG_ON(sb->s_options);
1267     rcu_assign_pointer(sb->s_options, kstrdup(options, GFP_KERNEL));
1268 }
1269 EXPORT_SYMBOL(save_mount_options);
1270 
1271 void replace_mount_options(struct super_block *sb, char *options)
1272 {
1273     char *old = sb->s_options;
1274     rcu_assign_pointer(sb->s_options, options);
1275     if (old) {
1276         synchronize_rcu();
1277         kfree(old);
1278     }
1279 }
1280 EXPORT_SYMBOL(replace_mount_options);
1281 
1282 #ifdef CONFIG_PROC_FS
1283 /* iterator; we want it to have access to namespace_sem, thus here... */
1284 static void *m_start(struct seq_file *m, loff_t *pos)
1285 {
1286     struct proc_mounts *p = m->private;
1287 
1288     down_read(&namespace_sem);
1289     if (p->cached_event == p->ns->event) {
1290         void *v = p->cached_mount;
1291         if (*pos == p->cached_index)
1292             return v;
1293         if (*pos == p->cached_index + 1) {
1294             v = seq_list_next(v, &p->ns->list, &p->cached_index);
1295             return p->cached_mount = v;
1296         }
1297     }
1298 
1299     p->cached_event = p->ns->event;
1300     p->cached_mount = seq_list_start(&p->ns->list, *pos);
1301     p->cached_index = *pos;
1302     return p->cached_mount;
1303 }
1304 
1305 static void *m_next(struct seq_file *m, void *v, loff_t *pos)
1306 {
1307     struct proc_mounts *p = m->private;
1308 
1309     p->cached_mount = seq_list_next(v, &p->ns->list, pos);
1310     p->cached_index = *pos;
1311     return p->cached_mount;
1312 }
1313 
1314 static void m_stop(struct seq_file *m, void *v)
1315 {
1316     up_read(&namespace_sem);
1317 }
1318 
1319 static int m_show(struct seq_file *m, void *v)
1320 {
1321     struct proc_mounts *p = m->private;
1322     struct mount *r = list_entry(v, struct mount, mnt_list);
1323     return p->show(m, &r->mnt);
1324 }
1325 
1326 const struct seq_operations mounts_op = {
1327     .start  = m_start,
1328     .next   = m_next,
1329     .stop   = m_stop,
1330     .show   = m_show,
1331 };
1332 #endif  /* CONFIG_PROC_FS */
1333 
1334 /**
1335  * may_umount_tree - check if a mount tree is busy
1336  * @mnt: root of mount tree
1337  *
1338  * This is called to check if a tree of mounts has any
1339  * open files, pwds, chroots or sub mounts that are
1340  * busy.
1341  */
1342 int may_umount_tree(struct vfsmount *m)
1343 {
1344     struct mount *mnt = real_mount(m);
1345     int actual_refs = 0;
1346     int minimum_refs = 0;
1347     struct mount *p;
1348     BUG_ON(!m);
1349 
1350     /* write lock needed for mnt_get_count */
1351     lock_mount_hash();
1352     for (p = mnt; p; p = next_mnt(p, mnt)) {
1353         actual_refs += mnt_get_count(p);
1354         minimum_refs += 2;
1355     }
1356     unlock_mount_hash();
1357 
1358     if (actual_refs > minimum_refs)
1359         return 0;
1360 
1361     return 1;
1362 }
1363 
1364 EXPORT_SYMBOL(may_umount_tree);
1365 
1366 /**
1367  * may_umount - check if a mount point is busy
1368  * @mnt: root of mount
1369  *
1370  * This is called to check if a mount point has any
1371  * open files, pwds, chroots or sub mounts. If the
1372  * mount has sub mounts this will return busy
1373  * regardless of whether the sub mounts are busy.
1374  *
1375  * Doesn't take quota and stuff into account. IOW, in some cases it will
1376  * give false negatives. The main reason why it's here is that we need
1377  * a non-destructive way to look for easily umountable filesystems.
1378  */
1379 int may_umount(struct vfsmount *mnt)
1380 {
1381     int ret = 1;
1382     down_read(&namespace_sem);
1383     lock_mount_hash();
1384     if (propagate_mount_busy(real_mount(mnt), 2))
1385         ret = 0;
1386     unlock_mount_hash();
1387     up_read(&namespace_sem);
1388     return ret;
1389 }
1390 
1391 EXPORT_SYMBOL(may_umount);
1392 
1393 static HLIST_HEAD(unmounted);   /* protected by namespace_sem */
1394 
1395 static void namespace_unlock(void)
1396 {
1397     struct hlist_head head;
1398 
1399     hlist_move_list(&unmounted, &head);
1400 
1401     up_write(&namespace_sem);
1402 
1403     if (likely(hlist_empty(&head)))
1404         return;
1405 
1406     synchronize_rcu();
1407 
1408     group_pin_kill(&head);
1409 }
1410 
1411 static inline void namespace_lock(void)
1412 {
1413     down_write(&namespace_sem);
1414 }
1415 
1416 enum umount_tree_flags {
1417     UMOUNT_SYNC = 1,
1418     UMOUNT_PROPAGATE = 2,
1419     UMOUNT_CONNECTED = 4,
1420 };
1421 
1422 static bool disconnect_mount(struct mount *mnt, enum umount_tree_flags how)
1423 {
1424     /* Leaving mounts connected is only valid for lazy umounts */
1425     if (how & UMOUNT_SYNC)
1426         return true;
1427 
1428     /* A mount without a parent has nothing to be connected to */
1429     if (!mnt_has_parent(mnt))
1430         return true;
1431 
1432     /* Because the reference counting rules change when mounts are
1433      * unmounted and connected, umounted mounts may not be
1434      * connected to mounted mounts.
1435      */
1436     if (!(mnt->mnt_parent->mnt.mnt_flags & MNT_UMOUNT))
1437         return true;
1438 
1439     /* Has it been requested that the mount remain connected? */
1440     if (how & UMOUNT_CONNECTED)
1441         return false;
1442 
1443     /* Is the mount locked such that it needs to remain connected? */
1444     if (IS_MNT_LOCKED(mnt))
1445         return false;
1446 
1447     /* By default disconnect the mount */
1448     return true;
1449 }
1450 
1451 /*
1452  * mount_lock must be held
1453  * namespace_sem must be held for write
1454  */
1455 static void umount_tree(struct mount *mnt, enum umount_tree_flags how)
1456 {
1457     LIST_HEAD(tmp_list);
1458     struct mount *p;
1459 
1460     if (how & UMOUNT_PROPAGATE)
1461         propagate_mount_unlock(mnt);
1462 
1463     /* Gather the mounts to umount */
1464     for (p = mnt; p; p = next_mnt(p, mnt)) {
1465         p->mnt.mnt_flags |= MNT_UMOUNT;
1466         list_move(&p->mnt_list, &tmp_list);
1467     }
1468 
1469     /* Hide the mounts from mnt_mounts */
1470     list_for_each_entry(p, &tmp_list, mnt_list) {
1471         list_del_init(&p->mnt_child);
1472     }
1473 
1474     /* Add propogated mounts to the tmp_list */
1475     if (how & UMOUNT_PROPAGATE)
1476         propagate_umount(&tmp_list);
1477 
1478     while (!list_empty(&tmp_list)) {
1479         struct mnt_namespace *ns;
1480         bool disconnect;
1481         p = list_first_entry(&tmp_list, struct mount, mnt_list);
1482         list_del_init(&p->mnt_expire);
1483         list_del_init(&p->mnt_list);
1484         ns = p->mnt_ns;
1485         if (ns) {
1486             ns->mounts--;
1487             __touch_mnt_namespace(ns);
1488         }
1489         p->mnt_ns = NULL;
1490         if (how & UMOUNT_SYNC)
1491             p->mnt.mnt_flags |= MNT_SYNC_UMOUNT;
1492 
1493         disconnect = disconnect_mount(p, how);
1494 
1495         pin_insert_group(&p->mnt_umount, &p->mnt_parent->mnt,
1496                  disconnect ? &unmounted : NULL);
1497         if (mnt_has_parent(p)) {
1498             mnt_add_count(p->mnt_parent, -1);
1499             if (!disconnect) {
1500                 /* Don't forget about p */
1501                 list_add_tail(&p->mnt_child, &p->mnt_parent->mnt_mounts);
1502             } else {
1503                 umount_mnt(p);
1504             }
1505         }
1506         change_mnt_propagation(p, MS_PRIVATE);
1507     }
1508 }
1509 
1510 static void shrink_submounts(struct mount *mnt);
1511 
1512 static int do_umount(struct mount *mnt, int flags)
1513 {
1514     struct super_block *sb = mnt->mnt.mnt_sb;
1515     int retval;
1516 
1517     retval = security_sb_umount(&mnt->mnt, flags);
1518     if (retval)
1519         return retval;
1520 
1521     /*
1522      * Allow userspace to request a mountpoint be expired rather than
1523      * unmounting unconditionally. Unmount only happens if:
1524      *  (1) the mark is already set (the mark is cleared by mntput())
1525      *  (2) the usage count == 1 [parent vfsmount] + 1 [sys_umount]
1526      */
1527     if (flags & MNT_EXPIRE) {
1528         if (&mnt->mnt == current->fs->root.mnt ||
1529             flags & (MNT_FORCE | MNT_DETACH))
1530             return -EINVAL;
1531 
1532         /*
1533          * probably don't strictly need the lock here if we examined
1534          * all race cases, but it's a slowpath.
1535          */
1536         lock_mount_hash();
1537         if (mnt_get_count(mnt) != 2) {
1538             unlock_mount_hash();
1539             return -EBUSY;
1540         }
1541         unlock_mount_hash();
1542 
1543         if (!xchg(&mnt->mnt_expiry_mark, 1))
1544             return -EAGAIN;
1545     }
1546 
1547     /*
1548      * If we may have to abort operations to get out of this
1549      * mount, and they will themselves hold resources we must
1550      * allow the fs to do things. In the Unix tradition of
1551      * 'Gee thats tricky lets do it in userspace' the umount_begin
1552      * might fail to complete on the first run through as other tasks
1553      * must return, and the like. Thats for the mount program to worry
1554      * about for the moment.
1555      */
1556 
1557     if (flags & MNT_FORCE && sb->s_op->umount_begin) {
1558         sb->s_op->umount_begin(sb);
1559     }
1560 
1561     /*
1562      * No sense to grab the lock for this test, but test itself looks
1563      * somewhat bogus. Suggestions for better replacement?
1564      * Ho-hum... In principle, we might treat that as umount + switch
1565      * to rootfs. GC would eventually take care of the old vfsmount.
1566      * Actually it makes sense, especially if rootfs would contain a
1567      * /reboot - static binary that would close all descriptors and
1568      * call reboot(9). Then init(8) could umount root and exec /reboot.
1569      */
1570     if (&mnt->mnt == current->fs->root.mnt && !(flags & MNT_DETACH)) {
1571         /*
1572          * Special case for "unmounting" root ...
1573          * we just try to remount it readonly.
1574          */
1575         if (!capable(CAP_SYS_ADMIN))
1576             return -EPERM;
1577         down_write(&sb->s_umount);
1578         if (!(sb->s_flags & MS_RDONLY))
1579             retval = do_remount_sb(sb, MS_RDONLY, NULL, 0);
1580         up_write(&sb->s_umount);
1581         return retval;
1582     }
1583 
1584     namespace_lock();
1585     lock_mount_hash();
1586     event++;
1587 
1588     if (flags & MNT_DETACH) {
1589         if (!list_empty(&mnt->mnt_list))
1590             umount_tree(mnt, UMOUNT_PROPAGATE);
1591         retval = 0;
1592     } else {
1593         shrink_submounts(mnt);
1594         retval = -EBUSY;
1595         if (!propagate_mount_busy(mnt, 2)) {
1596             if (!list_empty(&mnt->mnt_list))
1597                 umount_tree(mnt, UMOUNT_PROPAGATE|UMOUNT_SYNC);
1598             retval = 0;
1599         }
1600     }
1601     unlock_mount_hash();
1602     namespace_unlock();
1603     return retval;
1604 }
1605 
1606 /*
1607  * __detach_mounts - lazily unmount all mounts on the specified dentry
1608  *
1609  * During unlink, rmdir, and d_drop it is possible to loose the path
1610  * to an existing mountpoint, and wind up leaking the mount.
1611  * detach_mounts allows lazily unmounting those mounts instead of
1612  * leaking them.
1613  *
1614  * The caller may hold dentry->d_inode->i_mutex.
1615  */
1616 void __detach_mounts(struct dentry *dentry)
1617 {
1618     struct mountpoint *mp;
1619     struct mount *mnt;
1620 
1621     namespace_lock();
1622     lock_mount_hash();
1623     mp = lookup_mountpoint(dentry);
1624     if (IS_ERR_OR_NULL(mp))
1625         goto out_unlock;
1626 
1627     event++;
1628     while (!hlist_empty(&mp->m_list)) {
1629         mnt = hlist_entry(mp->m_list.first, struct mount, mnt_mp_list);
1630         if (mnt->mnt.mnt_flags & MNT_UMOUNT) {
1631             hlist_add_head(&mnt->mnt_umount.s_list, &unmounted);
1632             umount_mnt(mnt);
1633         }
1634         else umount_tree(mnt, UMOUNT_CONNECTED);
1635     }
1636     put_mountpoint(mp);
1637 out_unlock:
1638     unlock_mount_hash();
1639     namespace_unlock();
1640 }
1641 
1642 /* 
1643  * Is the caller allowed to modify his namespace?
1644  */
1645 static inline bool may_mount(void)
1646 {
1647     return ns_capable(current->nsproxy->mnt_ns->user_ns, CAP_SYS_ADMIN);
1648 }
1649 
1650 static inline bool may_mandlock(void)
1651 {
1652 #ifndef CONFIG_MANDATORY_FILE_LOCKING
1653     return false;
1654 #endif
1655     return capable(CAP_SYS_ADMIN);
1656 }
1657 
1658 /*
1659  * Now umount can handle mount points as well as block devices.
1660  * This is important for filesystems which use unnamed block devices.
1661  *
1662  * We now support a flag for forced unmount like the other 'big iron'
1663  * unixes. Our API is identical to OSF/1 to avoid making a mess of AMD
1664  */
1665 
1666 SYSCALL_DEFINE2(umount, char __user *, name, int, flags)
1667 {
1668     struct path path;
1669     struct mount *mnt;
1670     int retval;
1671     int lookup_flags = 0;
1672 
1673     if (flags & ~(MNT_FORCE | MNT_DETACH | MNT_EXPIRE | UMOUNT_NOFOLLOW))
1674         return -EINVAL;
1675 
1676     if (!may_mount())
1677         return -EPERM;
1678 
1679     if (!(flags & UMOUNT_NOFOLLOW))
1680         lookup_flags |= LOOKUP_FOLLOW;
1681 
1682     retval = user_path_mountpoint_at(AT_FDCWD, name, lookup_flags, &path);
1683     if (retval)
1684         goto out;
1685     mnt = real_mount(path.mnt);
1686     retval = -EINVAL;
1687     if (path.dentry != path.mnt->mnt_root)
1688         goto dput_and_out;
1689     if (!check_mnt(mnt))
1690         goto dput_and_out;
1691     if (mnt->mnt.mnt_flags & MNT_LOCKED)
1692         goto dput_and_out;
1693     retval = -EPERM;
1694     if (flags & MNT_FORCE && !capable(CAP_SYS_ADMIN))
1695         goto dput_and_out;
1696 
1697     retval = do_umount(mnt, flags);
1698 dput_and_out:
1699     /* we mustn't call path_put() as that would clear mnt_expiry_mark */
1700     dput(path.dentry);
1701     mntput_no_expire(mnt);
1702 out:
1703     return retval;
1704 }
1705 
1706 #ifdef __ARCH_WANT_SYS_OLDUMOUNT
1707 
1708 /*
1709  *  The 2.0 compatible umount. No flags.
1710  */
1711 SYSCALL_DEFINE1(oldumount, char __user *, name)
1712 {
1713     return sys_umount(name, 0);
1714 }
1715 
1716 #endif
1717 
1718 static bool is_mnt_ns_file(struct dentry *dentry)
1719 {
1720     /* Is this a proxy for a mount namespace? */
1721     return dentry->d_op == &ns_dentry_operations &&
1722            dentry->d_fsdata == &mntns_operations;
1723 }
1724 
1725 struct mnt_namespace *to_mnt_ns(struct ns_common *ns)
1726 {
1727     return container_of(ns, struct mnt_namespace, ns);
1728 }
1729 
1730 static bool mnt_ns_loop(struct dentry *dentry)
1731 {
1732     /* Could bind mounting the mount namespace inode cause a
1733      * mount namespace loop?
1734      */
1735     struct mnt_namespace *mnt_ns;
1736     if (!is_mnt_ns_file(dentry))
1737         return false;
1738 
1739     mnt_ns = to_mnt_ns(get_proc_ns(dentry->d_inode));
1740     return current->nsproxy->mnt_ns->seq >= mnt_ns->seq;
1741 }
1742 
1743 struct mount *copy_tree(struct mount *mnt, struct dentry *dentry,
1744                     int flag)
1745 {
1746     struct mount *res, *p, *q, *r, *parent;
1747 
1748     if (!(flag & CL_COPY_UNBINDABLE) && IS_MNT_UNBINDABLE(mnt))
1749         return ERR_PTR(-EINVAL);
1750 
1751     if (!(flag & CL_COPY_MNT_NS_FILE) && is_mnt_ns_file(dentry))
1752         return ERR_PTR(-EINVAL);
1753 
1754     res = q = clone_mnt(mnt, dentry, flag);
1755     if (IS_ERR(q))
1756         return q;
1757 
1758     q->mnt_mountpoint = mnt->mnt_mountpoint;
1759 
1760     p = mnt;
1761     list_for_each_entry(r, &mnt->mnt_mounts, mnt_child) {
1762         struct mount *s;
1763         if (!is_subdir(r->mnt_mountpoint, dentry))
1764             continue;
1765 
1766         for (s = r; s; s = next_mnt(s, r)) {
1767             struct mount *t = NULL;
1768             if (!(flag & CL_COPY_UNBINDABLE) &&
1769                 IS_MNT_UNBINDABLE(s)) {
1770                 s = skip_mnt_tree(s);
1771                 continue;
1772             }
1773             if (!(flag & CL_COPY_MNT_NS_FILE) &&
1774                 is_mnt_ns_file(s->mnt.mnt_root)) {
1775                 s = skip_mnt_tree(s);
1776                 continue;
1777             }
1778             while (p != s->mnt_parent) {
1779                 p = p->mnt_parent;
1780                 q = q->mnt_parent;
1781             }
1782             p = s;
1783             parent = q;
1784             q = clone_mnt(p, p->mnt.mnt_root, flag);
1785             if (IS_ERR(q))
1786                 goto out;
1787             lock_mount_hash();
1788             list_add_tail(&q->mnt_list, &res->mnt_list);
1789             mnt_set_mountpoint(parent, p->mnt_mp, q);
1790             if (!list_empty(&parent->mnt_mounts)) {
1791                 t = list_last_entry(&parent->mnt_mounts,
1792                     struct mount, mnt_child);
1793                 if (t->mnt_mp != p->mnt_mp)
1794                     t = NULL;
1795             }
1796             attach_shadowed(q, parent, t);
1797             unlock_mount_hash();
1798         }
1799     }
1800     return res;
1801 out:
1802     if (res) {
1803         lock_mount_hash();
1804         umount_tree(res, UMOUNT_SYNC);
1805         unlock_mount_hash();
1806     }
1807     return q;
1808 }
1809 
1810 /* Caller should check returned pointer for errors */
1811 
1812 struct vfsmount *collect_mounts(const struct path *path)
1813 {
1814     struct mount *tree;
1815     namespace_lock();
1816     if (!check_mnt(real_mount(path->mnt)))
1817         tree = ERR_PTR(-EINVAL);
1818     else
1819         tree = copy_tree(real_mount(path->mnt), path->dentry,
1820                  CL_COPY_ALL | CL_PRIVATE);
1821     namespace_unlock();
1822     if (IS_ERR(tree))
1823         return ERR_CAST(tree);
1824     return &tree->mnt;
1825 }
1826 
1827 void drop_collected_mounts(struct vfsmount *mnt)
1828 {
1829     namespace_lock();
1830     lock_mount_hash();
1831     umount_tree(real_mount(mnt), UMOUNT_SYNC);
1832     unlock_mount_hash();
1833     namespace_unlock();
1834 }
1835 
1836 /**
1837  * clone_private_mount - create a private clone of a path
1838  *
1839  * This creates a new vfsmount, which will be the clone of @path.  The new will
1840  * not be attached anywhere in the namespace and will be private (i.e. changes
1841  * to the originating mount won't be propagated into this).
1842  *
1843  * Release with mntput().
1844  */
1845 struct vfsmount *clone_private_mount(const struct path *path)
1846 {
1847     struct mount *old_mnt = real_mount(path->mnt);
1848     struct mount *new_mnt;
1849 
1850     if (IS_MNT_UNBINDABLE(old_mnt))
1851         return ERR_PTR(-EINVAL);
1852 
1853     new_mnt = clone_mnt(old_mnt, path->dentry, CL_PRIVATE);
1854     if (IS_ERR(new_mnt))
1855         return ERR_CAST(new_mnt);
1856 
1857     return &new_mnt->mnt;
1858 }
1859 EXPORT_SYMBOL_GPL(clone_private_mount);
1860 
1861 int iterate_mounts(int (*f)(struct vfsmount *, void *), void *arg,
1862            struct vfsmount *root)
1863 {
1864     struct mount *mnt;
1865     int res = f(root, arg);
1866     if (res)
1867         return res;
1868     list_for_each_entry(mnt, &real_mount(root)->mnt_list, mnt_list) {
1869         res = f(&mnt->mnt, arg);
1870         if (res)
1871             return res;
1872     }
1873     return 0;
1874 }
1875 
1876 static void cleanup_group_ids(struct mount *mnt, struct mount *end)
1877 {
1878     struct mount *p;
1879 
1880     for (p = mnt; p != end; p = next_mnt(p, mnt)) {
1881         if (p->mnt_group_id && !IS_MNT_SHARED(p))
1882             mnt_release_group_id(p);
1883     }
1884 }
1885 
1886 static int invent_group_ids(struct mount *mnt, bool recurse)
1887 {
1888     struct mount *p;
1889 
1890     for (p = mnt; p; p = recurse ? next_mnt(p, mnt) : NULL) {
1891         if (!p->mnt_group_id && !IS_MNT_SHARED(p)) {
1892             int err = mnt_alloc_group_id(p);
1893             if (err) {
1894                 cleanup_group_ids(mnt, p);
1895                 return err;
1896             }
1897         }
1898     }
1899 
1900     return 0;
1901 }
1902 
1903 int count_mounts(struct mnt_namespace *ns, struct mount *mnt)
1904 {
1905     unsigned int max = READ_ONCE(sysctl_mount_max);
1906     unsigned int mounts = 0, old, pending, sum;
1907     struct mount *p;
1908 
1909     for (p = mnt; p; p = next_mnt(p, mnt))
1910         mounts++;
1911 
1912     old = ns->mounts;
1913     pending = ns->pending_mounts;
1914     sum = old + pending;
1915     if ((old > sum) ||
1916         (pending > sum) ||
1917         (max < sum) ||
1918         (mounts > (max - sum)))
1919         return -ENOSPC;
1920 
1921     ns->pending_mounts = pending + mounts;
1922     return 0;
1923 }
1924 
1925 /*
1926  *  @source_mnt : mount tree to be attached
1927  *  @nd         : place the mount tree @source_mnt is attached
1928  *  @parent_nd  : if non-null, detach the source_mnt from its parent and
1929  *             store the parent mount and mountpoint dentry.
1930  *             (done when source_mnt is moved)
1931  *
1932  *  NOTE: in the table below explains the semantics when a source mount
1933  *  of a given type is attached to a destination mount of a given type.
1934  * ---------------------------------------------------------------------------
1935  * |         BIND MOUNT OPERATION                                            |
1936  * |**************************************************************************
1937  * | source-->| shared        |       private  |       slave    | unbindable |
1938  * | dest     |               |                |                |            |
1939  * |   |      |               |                |                |            |
1940  * |   v      |               |                |                |            |
1941  * |**************************************************************************
1942  * |  shared  | shared (++)   |     shared (+) |     shared(+++)|  invalid   |
1943  * |          |               |                |                |            |
1944  * |non-shared| shared (+)    |      private   |      slave (*) |  invalid   |
1945  * ***************************************************************************
1946  * A bind operation clones the source mount and mounts the clone on the
1947  * destination mount.
1948  *
1949  * (++)  the cloned mount is propagated to all the mounts in the propagation
1950  *   tree of the destination mount and the cloned mount is added to
1951  *   the peer group of the source mount.
1952  * (+)   the cloned mount is created under the destination mount and is marked
1953  *       as shared. The cloned mount is added to the peer group of the source
1954  *       mount.
1955  * (+++) the mount is propagated to all the mounts in the propagation tree
1956  *       of the destination mount and the cloned mount is made slave
1957  *       of the same master as that of the source mount. The cloned mount
1958  *       is marked as 'shared and slave'.
1959  * (*)   the cloned mount is made a slave of the same master as that of the
1960  *   source mount.
1961  *
1962  * ---------------------------------------------------------------------------
1963  * |                MOVE MOUNT OPERATION                                 |
1964  * |**************************************************************************
1965  * | source-->| shared        |       private  |       slave    | unbindable |
1966  * | dest     |               |                |                |            |
1967  * |   |      |               |                |                |            |
1968  * |   v      |               |                |                |            |
1969  * |**************************************************************************
1970  * |  shared  | shared (+)    |     shared (+) |    shared(+++) |  invalid   |
1971  * |          |               |                |                |            |
1972  * |non-shared| shared (+*)   |      private   |    slave (*)   | unbindable |
1973  * ***************************************************************************
1974  *
1975  * (+)  the mount is moved to the destination. And is then propagated to
1976  *  all the mounts in the propagation tree of the destination mount.
1977  * (+*)  the mount is moved to the destination.
1978  * (+++)  the mount is moved to the destination and is then propagated to
1979  *  all the mounts belonging to the destination mount's propagation tree.
1980  *  the mount is marked as 'shared and slave'.
1981  * (*)  the mount continues to be a slave at the new location.
1982  *
1983  * if the source mount is a tree, the operations explained above is
1984  * applied to each mount in the tree.
1985  * Must be called without spinlocks held, since this function can sleep
1986  * in allocations.
1987  */
1988 static int attach_recursive_mnt(struct mount *source_mnt,
1989             struct mount *dest_mnt,
1990             struct mountpoint *dest_mp,
1991             struct path *parent_path)
1992 {
1993     HLIST_HEAD(tree_list);
1994     struct mnt_namespace *ns = dest_mnt->mnt_ns;
1995     struct mount *child, *p;
1996     struct hlist_node *n;
1997     int err;
1998 
1999     /* Is there space to add these mounts to the mount namespace? */
2000     if (!parent_path) {
2001         err = count_mounts(ns, source_mnt);
2002         if (err)
2003             goto out;
2004     }
2005 
2006     if (IS_MNT_SHARED(dest_mnt)) {
2007         err = invent_group_ids(source_mnt, true);
2008         if (err)
2009             goto out;
2010         err = propagate_mnt(dest_mnt, dest_mp, source_mnt, &tree_list);
2011         lock_mount_hash();
2012         if (err)
2013             goto out_cleanup_ids;
2014         for (p = source_mnt; p; p = next_mnt(p, source_mnt))
2015             set_mnt_shared(p);
2016     } else {
2017         lock_mount_hash();
2018     }
2019     if (parent_path) {
2020         detach_mnt(source_mnt, parent_path);
2021         attach_mnt(source_mnt, dest_mnt, dest_mp);
2022         touch_mnt_namespace(source_mnt->mnt_ns);
2023     } else {
2024         mnt_set_mountpoint(dest_mnt, dest_mp, source_mnt);
2025         commit_tree(source_mnt, NULL);
2026     }
2027 
2028     hlist_for_each_entry_safe(child, n, &tree_list, mnt_hash) {
2029         struct mount *q;
2030         hlist_del_init(&child->mnt_hash);
2031         q = __lookup_mnt_last(&child->mnt_parent->mnt,
2032                       child->mnt_mountpoint);
2033         commit_tree(child, q);
2034     }
2035     unlock_mount_hash();
2036 
2037     return 0;
2038 
2039  out_cleanup_ids:
2040     while (!hlist_empty(&tree_list)) {
2041         child = hlist_entry(tree_list.first, struct mount, mnt_hash);
2042         child->mnt_parent->mnt_ns->pending_mounts = 0;
2043         umount_tree(child, UMOUNT_SYNC);
2044     }
2045     unlock_mount_hash();
2046     cleanup_group_ids(source_mnt, NULL);
2047  out:
2048     ns->pending_mounts = 0;
2049     return err;
2050 }
2051 
2052 static struct mountpoint *lock_mount(struct path *path)
2053 {
2054     struct vfsmount *mnt;
2055     struct dentry *dentry = path->dentry;
2056 retry:
2057     inode_lock(dentry->d_inode);
2058     if (unlikely(cant_mount(dentry))) {
2059         inode_unlock(dentry->d_inode);
2060         return ERR_PTR(-ENOENT);
2061     }
2062     namespace_lock();
2063     mnt = lookup_mnt(path);
2064     if (likely(!mnt)) {
2065         struct mountpoint *mp = get_mountpoint(dentry);
2066         if (IS_ERR(mp)) {
2067             namespace_unlock();
2068             inode_unlock(dentry->d_inode);
2069             return mp;
2070         }
2071         return mp;
2072     }
2073     namespace_unlock();
2074     inode_unlock(path->dentry->d_inode);
2075     path_put(path);
2076     path->mnt = mnt;
2077     dentry = path->dentry = dget(mnt->mnt_root);
2078     goto retry;
2079 }
2080 
2081 static void unlock_mount(struct mountpoint *where)
2082 {
2083     struct dentry *dentry = where->m_dentry;
2084 
2085     read_seqlock_excl(&mount_lock);
2086     put_mountpoint(where);
2087     read_sequnlock_excl(&mount_lock);
2088 
2089     namespace_unlock();
2090     inode_unlock(dentry->d_inode);
2091 }
2092 
2093 static int graft_tree(struct mount *mnt, struct mount *p, struct mountpoint *mp)
2094 {
2095     if (mnt->mnt.mnt_sb->s_flags & MS_NOUSER)
2096         return -EINVAL;
2097 
2098     if (d_is_dir(mp->m_dentry) !=
2099           d_is_dir(mnt->mnt.mnt_root))
2100         return -ENOTDIR;
2101 
2102     return attach_recursive_mnt(mnt, p, mp, NULL);
2103 }
2104 
2105 /*
2106  * Sanity check the flags to change_mnt_propagation.
2107  */
2108 
2109 static int flags_to_propagation_type(int flags)
2110 {
2111     int type = flags & ~(MS_REC | MS_SILENT);
2112 
2113     /* Fail if any non-propagation flags are set */
2114     if (type & ~(MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
2115         return 0;
2116     /* Only one propagation flag should be set */
2117     if (!is_power_of_2(type))
2118         return 0;
2119     return type;
2120 }
2121 
2122 /*
2123  * recursively change the type of the mountpoint.
2124  */
2125 static int do_change_type(struct path *path, int flag)
2126 {
2127     struct mount *m;
2128     struct mount *mnt = real_mount(path->mnt);
2129     int recurse = flag & MS_REC;
2130     int type;
2131     int err = 0;
2132 
2133     if (path->dentry != path->mnt->mnt_root)
2134         return -EINVAL;
2135 
2136     type = flags_to_propagation_type(flag);
2137     if (!type)
2138         return -EINVAL;
2139 
2140     namespace_lock();
2141     if (type == MS_SHARED) {
2142         err = invent_group_ids(mnt, recurse);
2143         if (err)
2144             goto out_unlock;
2145     }
2146 
2147     lock_mount_hash();
2148     for (m = mnt; m; m = (recurse ? next_mnt(m, mnt) : NULL))
2149         change_mnt_propagation(m, type);
2150     unlock_mount_hash();
2151 
2152  out_unlock:
2153     namespace_unlock();
2154     return err;
2155 }
2156 
2157 static bool has_locked_children(struct mount *mnt, struct dentry *dentry)
2158 {
2159     struct mount *child;
2160     list_for_each_entry(child, &mnt->mnt_mounts, mnt_child) {
2161         if (!is_subdir(child->mnt_mountpoint, dentry))
2162             continue;
2163 
2164         if (child->mnt.mnt_flags & MNT_LOCKED)
2165             return true;
2166     }
2167     return false;
2168 }
2169 
2170 /*
2171  * do loopback mount.
2172  */
2173 static int do_loopback(struct path *path, const char *old_name,
2174                 int recurse)
2175 {
2176     struct path old_path;
2177     struct mount *mnt = NULL, *old, *parent;
2178     struct mountpoint *mp;
2179     int err;
2180     if (!old_name || !*old_name)
2181         return -EINVAL;
2182     err = kern_path(old_name, LOOKUP_FOLLOW|LOOKUP_AUTOMOUNT, &old_path);
2183     if (err)
2184         return err;
2185 
2186     err = -EINVAL;
2187     if (mnt_ns_loop(old_path.dentry))
2188         goto out; 
2189 
2190     mp = lock_mount(path);
2191     err = PTR_ERR(mp);
2192     if (IS_ERR(mp))
2193         goto out;
2194 
2195     old = real_mount(old_path.mnt);
2196     parent = real_mount(path->mnt);
2197 
2198     err = -EINVAL;
2199     if (IS_MNT_UNBINDABLE(old))
2200         goto out2;
2201 
2202     if (!check_mnt(parent))
2203         goto out2;
2204 
2205     if (!check_mnt(old) && old_path.dentry->d_op != &ns_dentry_operations)
2206         goto out2;
2207 
2208     if (!recurse && has_locked_children(old, old_path.dentry))
2209         goto out2;
2210 
2211     if (recurse)
2212         mnt = copy_tree(old, old_path.dentry, CL_COPY_MNT_NS_FILE);
2213     else
2214         mnt = clone_mnt(old, old_path.dentry, 0);
2215 
2216     if (IS_ERR(mnt)) {
2217         err = PTR_ERR(mnt);
2218         goto out2;
2219     }
2220 
2221     mnt->mnt.mnt_flags &= ~MNT_LOCKED;
2222 
2223     err = graft_tree(mnt, parent, mp);
2224     if (err) {
2225         lock_mount_hash();
2226         umount_tree(mnt, UMOUNT_SYNC);
2227         unlock_mount_hash();
2228     }
2229 out2:
2230     unlock_mount(mp);
2231 out:
2232     path_put(&old_path);
2233     return err;
2234 }
2235 
2236 static int change_mount_flags(struct vfsmount *mnt, int ms_flags)
2237 {
2238     int error = 0;
2239     int readonly_request = 0;
2240 
2241     if (ms_flags & MS_RDONLY)
2242         readonly_request = 1;
2243     if (readonly_request == __mnt_is_readonly(mnt))
2244         return 0;
2245 
2246     if (readonly_request)
2247         error = mnt_make_readonly(real_mount(mnt));
2248     else
2249         __mnt_unmake_readonly(real_mount(mnt));
2250     return error;
2251 }
2252 
2253 /*
2254  * change filesystem flags. dir should be a physical root of filesystem.
2255  * If you've mounted a non-root directory somewhere and want to do remount
2256  * on it - tough luck.
2257  */
2258 static int do_remount(struct path *path, int flags, int mnt_flags,
2259               void *data)
2260 {
2261     int err;
2262     struct super_block *sb = path->mnt->mnt_sb;
2263     struct mount *mnt = real_mount(path->mnt);
2264 
2265     if (!check_mnt(mnt))
2266         return -EINVAL;
2267 
2268     if (path->dentry != path->mnt->mnt_root)
2269         return -EINVAL;
2270 
2271     /* Don't allow changing of locked mnt flags.
2272      *
2273      * No locks need to be held here while testing the various
2274      * MNT_LOCK flags because those flags can never be cleared
2275      * once they are set.
2276      */
2277     if ((mnt->mnt.mnt_flags & MNT_LOCK_READONLY) &&
2278         !(mnt_flags & MNT_READONLY)) {
2279         return -EPERM;
2280     }
2281     if ((mnt->mnt.mnt_flags & MNT_LOCK_NODEV) &&
2282         !(mnt_flags & MNT_NODEV)) {
2283         return -EPERM;
2284     }
2285     if ((mnt->mnt.mnt_flags & MNT_LOCK_NOSUID) &&
2286         !(mnt_flags & MNT_NOSUID)) {
2287         return -EPERM;
2288     }
2289     if ((mnt->mnt.mnt_flags & MNT_LOCK_NOEXEC) &&
2290         !(mnt_flags & MNT_NOEXEC)) {
2291         return -EPERM;
2292     }
2293     if ((mnt->mnt.mnt_flags & MNT_LOCK_ATIME) &&
2294         ((mnt->mnt.mnt_flags & MNT_ATIME_MASK) != (mnt_flags & MNT_ATIME_MASK))) {
2295         return -EPERM;
2296     }
2297 
2298     err = security_sb_remount(sb, data);
2299     if (err)
2300         return err;
2301 
2302     down_write(&sb->s_umount);
2303     if (flags & MS_BIND)
2304         err = change_mount_flags(path->mnt, flags);
2305     else if (!capable(CAP_SYS_ADMIN))
2306         err = -EPERM;
2307     else
2308         err = do_remount_sb(sb, flags, data, 0);
2309     if (!err) {
2310         lock_mount_hash();
2311         mnt_flags |= mnt->mnt.mnt_flags & ~MNT_USER_SETTABLE_MASK;
2312         mnt->mnt.mnt_flags = mnt_flags;
2313         touch_mnt_namespace(mnt->mnt_ns);
2314         unlock_mount_hash();
2315     }
2316     up_write(&sb->s_umount);
2317     return err;
2318 }
2319 
2320 static inline int tree_contains_unbindable(struct mount *mnt)
2321 {
2322     struct mount *p;
2323     for (p = mnt; p; p = next_mnt(p, mnt)) {
2324         if (IS_MNT_UNBINDABLE(p))
2325             return 1;
2326     }
2327     return 0;
2328 }
2329 
2330 static int do_move_mount(struct path *path, const char *old_name)
2331 {
2332     struct path old_path, parent_path;
2333     struct mount *p;
2334     struct mount *old;
2335     struct mountpoint *mp;
2336     int err;
2337     if (!old_name || !*old_name)
2338         return -EINVAL;
2339     err = kern_path(old_name, LOOKUP_FOLLOW, &old_path);
2340     if (err)
2341         return err;
2342 
2343     mp = lock_mount(path);
2344     err = PTR_ERR(mp);
2345     if (IS_ERR(mp))
2346         goto out;
2347 
2348     old = real_mount(old_path.mnt);
2349     p = real_mount(path->mnt);
2350 
2351     err = -EINVAL;
2352     if (!check_mnt(p) || !check_mnt(old))
2353         goto out1;
2354 
2355     if (old->mnt.mnt_flags & MNT_LOCKED)
2356         goto out1;
2357 
2358     err = -EINVAL;
2359     if (old_path.dentry != old_path.mnt->mnt_root)
2360         goto out1;
2361 
2362     if (!mnt_has_parent(old))
2363         goto out1;
2364 
2365     if (d_is_dir(path->dentry) !=
2366           d_is_dir(old_path.dentry))
2367         goto out1;
2368     /*
2369      * Don't move a mount residing in a shared parent.
2370      */
2371     if (IS_MNT_SHARED(old->mnt_parent))
2372         goto out1;
2373     /*
2374      * Don't move a mount tree containing unbindable mounts to a destination
2375      * mount which is shared.
2376      */
2377     if (IS_MNT_SHARED(p) && tree_contains_unbindable(old))
2378         goto out1;
2379     err = -ELOOP;
2380     for (; mnt_has_parent(p); p = p->mnt_parent)
2381         if (p == old)
2382             goto out1;
2383 
2384     err = attach_recursive_mnt(old, real_mount(path->mnt), mp, &parent_path);
2385     if (err)
2386         goto out1;
2387 
2388     /* if the mount is moved, it should no longer be expire
2389      * automatically */
2390     list_del_init(&old->mnt_expire);
2391 out1:
2392     unlock_mount(mp);
2393 out:
2394     if (!err)
2395         path_put(&parent_path);
2396     path_put(&old_path);
2397     return err;
2398 }
2399 
2400 static struct vfsmount *fs_set_subtype(struct vfsmount *mnt, const char *fstype)
2401 {
2402     int err;
2403     const char *subtype = strchr(fstype, '.');
2404     if (subtype) {
2405         subtype++;
2406         err = -EINVAL;
2407         if (!subtype[0])
2408             goto err;
2409     } else
2410         subtype = "";
2411 
2412     mnt->mnt_sb->s_subtype = kstrdup(subtype, GFP_KERNEL);
2413     err = -ENOMEM;
2414     if (!mnt->mnt_sb->s_subtype)
2415         goto err;
2416     return mnt;
2417 
2418  err:
2419     mntput(mnt);
2420     return ERR_PTR(err);
2421 }
2422 
2423 /*
2424  * add a mount into a namespace's mount tree
2425  */
2426 static int do_add_mount(struct mount *newmnt, struct path *path, int mnt_flags)
2427 {
2428     struct mountpoint *mp;
2429     struct mount *parent;
2430     int err;
2431 
2432     mnt_flags &= ~MNT_INTERNAL_FLAGS;
2433 
2434     mp = lock_mount(path);
2435     if (IS_ERR(mp))
2436         return PTR_ERR(mp);
2437 
2438     parent = real_mount(path->mnt);
2439     err = -EINVAL;
2440     if (unlikely(!check_mnt(parent))) {
2441         /* that's acceptable only for automounts done in private ns */
2442         if (!(mnt_flags & MNT_SHRINKABLE))
2443             goto unlock;
2444         /* ... and for those we'd better have mountpoint still alive */
2445         if (!parent->mnt_ns)
2446             goto unlock;
2447     }
2448 
2449     /* Refuse the same filesystem on the same mount point */
2450     err = -EBUSY;
2451     if (path->mnt->mnt_sb == newmnt->mnt.mnt_sb &&
2452         path->mnt->mnt_root == path->dentry)
2453         goto unlock;
2454 
2455     err = -EINVAL;
2456     if (d_is_symlink(newmnt->mnt.mnt_root))
2457         goto unlock;
2458 
2459     newmnt->mnt.mnt_flags = mnt_flags;
2460     err = graft_tree(newmnt, parent, mp);
2461 
2462 unlock:
2463     unlock_mount(mp);
2464     return err;
2465 }
2466 
2467 static bool mount_too_revealing(struct vfsmount *mnt, int *new_mnt_flags);
2468 
2469 /*
2470  * create a new mount for userspace and request it to be added into the
2471  * namespace's tree
2472  */
2473 static int do_new_mount(struct path *path, const char *fstype, int flags,
2474             int mnt_flags, const char *name, void *data)
2475 {
2476     struct file_system_type *type;
2477     struct vfsmount *mnt;
2478     int err;
2479 
2480     if (!fstype)
2481         return -EINVAL;
2482 
2483     type = get_fs_type(fstype);
2484     if (!type)
2485         return -ENODEV;
2486 
2487     mnt = vfs_kern_mount(type, flags, name, data);
2488     if (!IS_ERR(mnt) && (type->fs_flags & FS_HAS_SUBTYPE) &&
2489         !mnt->mnt_sb->s_subtype)
2490         mnt = fs_set_subtype(mnt, fstype);
2491 
2492     put_filesystem(type);
2493     if (IS_ERR(mnt))
2494         return PTR_ERR(mnt);
2495 
2496     if (mount_too_revealing(mnt, &mnt_flags)) {
2497         mntput(mnt);
2498         return -EPERM;
2499     }
2500 
2501     err = do_add_mount(real_mount(mnt), path, mnt_flags);
2502     if (err)
2503         mntput(mnt);
2504     return err;
2505 }
2506 
2507 int finish_automount(struct vfsmount *m, struct path *path)
2508 {
2509     struct mount *mnt = real_mount(m);
2510     int err;
2511     /* The new mount record should have at least 2 refs to prevent it being
2512      * expired before we get a chance to add it
2513      */
2514     BUG_ON(mnt_get_count(mnt) < 2);
2515 
2516     if (m->mnt_sb == path->mnt->mnt_sb &&
2517         m->mnt_root == path->dentry) {
2518         err = -ELOOP;
2519         goto fail;
2520     }
2521 
2522     err = do_add_mount(mnt, path, path->mnt->mnt_flags | MNT_SHRINKABLE);
2523     if (!err)
2524         return 0;
2525 fail:
2526     /* remove m from any expiration list it may be on */
2527     if (!list_empty(&mnt->mnt_expire)) {
2528         namespace_lock();
2529         list_del_init(&mnt->mnt_expire);
2530         namespace_unlock();
2531     }
2532     mntput(m);
2533     mntput(m);
2534     return err;
2535 }
2536 
2537 /**
2538  * mnt_set_expiry - Put a mount on an expiration list
2539  * @mnt: The mount to list.
2540  * @expiry_list: The list to add the mount to.
2541  */
2542 void mnt_set_expiry(struct vfsmount *mnt, struct list_head *expiry_list)
2543 {
2544     namespace_lock();
2545 
2546     list_add_tail(&real_mount(mnt)->mnt_expire, expiry_list);
2547 
2548     namespace_unlock();
2549 }
2550 EXPORT_SYMBOL(mnt_set_expiry);
2551 
2552 /*
2553  * process a list of expirable mountpoints with the intent of discarding any
2554  * mountpoints that aren't in use and haven't been touched since last we came
2555  * here
2556  */
2557 void mark_mounts_for_expiry(struct list_head *mounts)
2558 {
2559     struct mount *mnt, *next;
2560     LIST_HEAD(graveyard);
2561 
2562     if (list_empty(mounts))
2563         return;
2564 
2565     namespace_lock();
2566     lock_mount_hash();
2567 
2568     /* extract from the expiration list every vfsmount that matches the
2569      * following criteria:
2570      * - only referenced by its parent vfsmount
2571      * - still marked for expiry (marked on the last call here; marks are
2572      *   cleared by mntput())
2573      */
2574     list_for_each_entry_safe(mnt, next, mounts, mnt_expire) {
2575         if (!xchg(&mnt->mnt_expiry_mark, 1) ||
2576             propagate_mount_busy(mnt, 1))
2577             continue;
2578         list_move(&mnt->mnt_expire, &graveyard);
2579     }
2580     while (!list_empty(&graveyard)) {
2581         mnt = list_first_entry(&graveyard, struct mount, mnt_expire);
2582         touch_mnt_namespace(mnt->mnt_ns);
2583         umount_tree(mnt, UMOUNT_PROPAGATE|UMOUNT_SYNC);
2584     }
2585     unlock_mount_hash();
2586     namespace_unlock();
2587 }
2588 
2589 EXPORT_SYMBOL_GPL(mark_mounts_for_expiry);
2590 
2591 /*
2592  * Ripoff of 'select_parent()'
2593  *
2594  * search the list of submounts for a given mountpoint, and move any
2595  * shrinkable submounts to the 'graveyard' list.
2596  */
2597 static int select_submounts(struct mount *parent, struct list_head *graveyard)
2598 {
2599     struct mount *this_parent = parent;
2600     struct list_head *next;
2601     int found = 0;
2602 
2603 repeat:
2604     next = this_parent->mnt_mounts.next;
2605 resume:
2606     while (next != &this_parent->mnt_mounts) {
2607         struct list_head *tmp = next;
2608         struct mount *mnt = list_entry(tmp, struct mount, mnt_child);
2609 
2610         next = tmp->next;
2611         if (!(mnt->mnt.mnt_flags & MNT_SHRINKABLE))
2612             continue;
2613         /*
2614          * Descend a level if the d_mounts list is non-empty.
2615          */
2616         if (!list_empty(&mnt->mnt_mounts)) {
2617             this_parent = mnt;
2618             goto repeat;
2619         }
2620 
2621         if (!propagate_mount_busy(mnt, 1)) {
2622             list_move_tail(&mnt->mnt_expire, graveyard);
2623             found++;
2624         }
2625     }
2626     /*
2627      * All done at this level ... ascend and resume the search
2628      */
2629     if (this_parent != parent) {
2630         next = this_parent->mnt_child.next;
2631         this_parent = this_parent->mnt_parent;
2632         goto resume;
2633     }
2634     return found;
2635 }
2636 
2637 /*
2638  * process a list of expirable mountpoints with the intent of discarding any
2639  * submounts of a specific parent mountpoint
2640  *
2641  * mount_lock must be held for write
2642  */
2643 static void shrink_submounts(struct mount *mnt)
2644 {
2645     LIST_HEAD(graveyard);
2646     struct mount *m;
2647 
2648     /* extract submounts of 'mountpoint' from the expiration list */
2649     while (select_submounts(mnt, &graveyard)) {
2650         while (!list_empty(&graveyard)) {
2651             m = list_first_entry(&graveyard, struct mount,
2652                         mnt_expire);
2653             touch_mnt_namespace(m->mnt_ns);
2654             umount_tree(m, UMOUNT_PROPAGATE|UMOUNT_SYNC);
2655         }
2656     }
2657 }
2658 
2659 /*
2660  * Some copy_from_user() implementations do not return the exact number of
2661  * bytes remaining to copy on a fault.  But copy_mount_options() requires that.
2662  * Note that this function differs from copy_from_user() in that it will oops
2663  * on bad values of `to', rather than returning a short copy.
2664  */
2665 static long exact_copy_from_user(void *to, const void __user * from,
2666                  unsigned long n)
2667 {
2668     char *t = to;
2669     const char __user *f = from;
2670     char c;
2671 
2672     if (!access_ok(VERIFY_READ, from, n))
2673         return n;
2674 
2675     while (n) {
2676         if (__get_user(c, f)) {
2677             memset(t, 0, n);
2678             break;
2679         }
2680         *t++ = c;
2681         f++;
2682         n--;
2683     }
2684     return n;
2685 }
2686 
2687 void *copy_mount_options(const void __user * data)
2688 {
2689     int i;
2690     unsigned long size;
2691     char *copy;
2692 
2693     if (!data)
2694         return NULL;
2695 
2696     copy = kmalloc(PAGE_SIZE, GFP_KERNEL);
2697     if (!copy)
2698         return ERR_PTR(-ENOMEM);
2699 
2700     /* We only care that *some* data at the address the user
2701      * gave us is valid.  Just in case, we'll zero
2702      * the remainder of the page.
2703      */
2704     /* copy_from_user cannot cross TASK_SIZE ! */
2705     size = TASK_SIZE - (unsigned long)data;
2706     if (size > PAGE_SIZE)
2707         size = PAGE_SIZE;
2708 
2709     i = size - exact_copy_from_user(copy, data, size);
2710     if (!i) {
2711         kfree(copy);
2712         return ERR_PTR(-EFAULT);
2713     }
2714     if (i != PAGE_SIZE)
2715         memset(copy + i, 0, PAGE_SIZE - i);
2716     return copy;
2717 }
2718 
2719 char *copy_mount_string(const void __user *data)
2720 {
2721     return data ? strndup_user(data, PAGE_SIZE) : NULL;
2722 }
2723 
2724 /*
2725  * Flags is a 32-bit value that allows up to 31 non-fs dependent flags to
2726  * be given to the mount() call (ie: read-only, no-dev, no-suid etc).
2727  *
2728  * data is a (void *) that can point to any structure up to
2729  * PAGE_SIZE-1 bytes, which can contain arbitrary fs-dependent
2730  * information (or be NULL).
2731  *
2732  * Pre-0.97 versions of mount() didn't have a flags word.
2733  * When the flags word was introduced its top half was required
2734  * to have the magic value 0xC0ED, and this remained so until 2.4.0-test9.
2735  * Therefore, if this magic number is present, it carries no information
2736  * and must be discarded.
2737  */
2738 long do_mount(const char *dev_name, const char __user *dir_name,
2739         const char *type_page, unsigned long flags, void *data_page)
2740 {
2741     struct path path;
2742     int retval = 0;
2743     int mnt_flags = 0;
2744 
2745     /* Discard magic */
2746     if ((flags & MS_MGC_MSK) == MS_MGC_VAL)
2747         flags &= ~MS_MGC_MSK;
2748 
2749     /* Basic sanity checks */
2750     if (data_page)
2751         ((char *)data_page)[PAGE_SIZE - 1] = 0;
2752 
2753     /* ... and get the mountpoint */
2754     retval = user_path(dir_name, &path);
2755     if (retval)
2756         return retval;
2757 
2758     retval = security_sb_mount(dev_name, &path,
2759                    type_page, flags, data_page);
2760     if (!retval && !may_mount())
2761         retval = -EPERM;
2762     if (!retval && (flags & MS_MANDLOCK) && !may_mandlock())
2763         retval = -EPERM;
2764     if (retval)
2765         goto dput_out;
2766 
2767     /* Default to relatime unless overriden */
2768     if (!(flags & MS_NOATIME))
2769         mnt_flags |= MNT_RELATIME;
2770 
2771     /* Separate the per-mountpoint flags */
2772     if (flags & MS_NOSUID)
2773         mnt_flags |= MNT_NOSUID;
2774     if (flags & MS_NODEV)
2775         mnt_flags |= MNT_NODEV;
2776     if (flags & MS_NOEXEC)
2777         mnt_flags |= MNT_NOEXEC;
2778     if (flags & MS_NOATIME)
2779         mnt_flags |= MNT_NOATIME;
2780     if (flags & MS_NODIRATIME)
2781         mnt_flags |= MNT_NODIRATIME;
2782     if (flags & MS_STRICTATIME)
2783         mnt_flags &= ~(MNT_RELATIME | MNT_NOATIME);
2784     if (flags & MS_RDONLY)
2785         mnt_flags |= MNT_READONLY;
2786 
2787     /* The default atime for remount is preservation */
2788     if ((flags & MS_REMOUNT) &&
2789         ((flags & (MS_NOATIME | MS_NODIRATIME | MS_RELATIME |
2790                MS_STRICTATIME)) == 0)) {
2791         mnt_flags &= ~MNT_ATIME_MASK;
2792         mnt_flags |= path.mnt->mnt_flags & MNT_ATIME_MASK;
2793     }
2794 
2795     flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE | MS_BORN |
2796            MS_NOATIME | MS_NODIRATIME | MS_RELATIME| MS_KERNMOUNT |
2797            MS_STRICTATIME | MS_NOREMOTELOCK);
2798 
2799     if (flags & MS_REMOUNT)
2800         retval = do_remount(&path, flags & ~MS_REMOUNT, mnt_flags,
2801                     data_page);
2802     else if (flags & MS_BIND)
2803         retval = do_loopback(&path, dev_name, flags & MS_REC);
2804     else if (flags & (MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
2805         retval = do_change_type(&path, flags);
2806     else if (flags & MS_MOVE)
2807         retval = do_move_mount(&path, dev_name);
2808     else
2809         retval = do_new_mount(&path, type_page, flags, mnt_flags,
2810                       dev_name, data_page);
2811 dput_out:
2812     path_put(&path);
2813     return retval;
2814 }
2815 
2816 static struct ucounts *inc_mnt_namespaces(struct user_namespace *ns)
2817 {
2818     return inc_ucount(ns, current_euid(), UCOUNT_MNT_NAMESPACES);
2819 }
2820 
2821 static void dec_mnt_namespaces(struct ucounts *ucounts)
2822 {
2823     dec_ucount(ucounts, UCOUNT_MNT_NAMESPACES);
2824 }
2825 
2826 static void free_mnt_ns(struct mnt_namespace *ns)
2827 {
2828     ns_free_inum(&ns->ns);
2829     dec_mnt_namespaces(ns->ucounts);
2830     put_user_ns(ns->user_ns);
2831     kfree(ns);
2832 }
2833 
2834 /*
2835  * Assign a sequence number so we can detect when we attempt to bind
2836  * mount a reference to an older mount namespace into the current
2837  * mount namespace, preventing reference counting loops.  A 64bit
2838  * number incrementing at 10Ghz will take 12,427 years to wrap which
2839  * is effectively never, so we can ignore the possibility.
2840  */
2841 static atomic64_t mnt_ns_seq = ATOMIC64_INIT(1);
2842 
2843 static struct mnt_namespace *alloc_mnt_ns(struct user_namespace *user_ns)
2844 {
2845     struct mnt_namespace *new_ns;
2846     struct ucounts *ucounts;
2847     int ret;
2848 
2849     ucounts = inc_mnt_namespaces(user_ns);
2850     if (!ucounts)
2851         return ERR_PTR(-ENOSPC);
2852 
2853     new_ns = kmalloc(sizeof(struct mnt_namespace), GFP_KERNEL);
2854     if (!new_ns) {
2855         dec_mnt_namespaces(ucounts);
2856         return ERR_PTR(-ENOMEM);
2857     }
2858     ret = ns_alloc_inum(&new_ns->ns);
2859     if (ret) {
2860         kfree(new_ns);
2861         dec_mnt_namespaces(ucounts);
2862         return ERR_PTR(ret);
2863     }
2864     new_ns->ns.ops = &mntns_operations;
2865     new_ns->seq = atomic64_add_return(1, &mnt_ns_seq);
2866     atomic_set(&new_ns->count, 1);
2867     new_ns->root = NULL;
2868     INIT_LIST_HEAD(&new_ns->list);
2869     init_waitqueue_head(&new_ns->poll);
2870     new_ns->event = 0;
2871     new_ns->user_ns = get_user_ns(user_ns);
2872     new_ns->ucounts = ucounts;
2873     new_ns->mounts = 0;
2874     new_ns->pending_mounts = 0;
2875     return new_ns;
2876 }
2877 
2878 __latent_entropy
2879 struct mnt_namespace *copy_mnt_ns(unsigned long flags, struct mnt_namespace *ns,
2880         struct user_namespace *user_ns, struct fs_struct *new_fs)
2881 {
2882     struct mnt_namespace *new_ns;
2883     struct vfsmount *rootmnt = NULL, *pwdmnt = NULL;
2884     struct mount *p, *q;
2885     struct mount *old;
2886     struct mount *new;
2887     int copy_flags;
2888 
2889     BUG_ON(!ns);
2890 
2891     if (likely(!(flags & CLONE_NEWNS))) {
2892         get_mnt_ns(ns);
2893         return ns;
2894     }
2895 
2896     old = ns->root;
2897 
2898     new_ns = alloc_mnt_ns(user_ns);
2899     if (IS_ERR(new_ns))
2900         return new_ns;
2901 
2902     namespace_lock();
2903     /* First pass: copy the tree topology */
2904     copy_flags = CL_COPY_UNBINDABLE | CL_EXPIRE;
2905     if (user_ns != ns->user_ns)
2906         copy_flags |= CL_SHARED_TO_SLAVE | CL_UNPRIVILEGED;
2907     new = copy_tree(old, old->mnt.mnt_root, copy_flags);
2908     if (IS_ERR(new)) {
2909         namespace_unlock();
2910         free_mnt_ns(new_ns);
2911         return ERR_CAST(new);
2912     }
2913     new_ns->root = new;
2914     list_add_tail(&new_ns->list, &new->mnt_list);
2915 
2916     /*
2917      * Second pass: switch the tsk->fs->* elements and mark new vfsmounts
2918      * as belonging to new namespace.  We have already acquired a private
2919      * fs_struct, so tsk->fs->lock is not needed.
2920      */
2921     p = old;
2922     q = new;
2923     while (p) {
2924         q->mnt_ns = new_ns;
2925         new_ns->mounts++;
2926         if (new_fs) {
2927             if (&p->mnt == new_fs->root.mnt) {
2928                 new_fs->root.mnt = mntget(&q->mnt);
2929                 rootmnt = &p->mnt;
2930             }
2931             if (&p->mnt == new_fs->pwd.mnt) {
2932                 new_fs->pwd.mnt = mntget(&q->mnt);
2933                 pwdmnt = &p->mnt;
2934             }
2935         }
2936         p = next_mnt(p, old);
2937         q = next_mnt(q, new);
2938         if (!q)
2939             break;
2940         while (p->mnt.mnt_root != q->mnt.mnt_root)
2941             p = next_mnt(p, old);
2942     }
2943     namespace_unlock();
2944 
2945     if (rootmnt)
2946         mntput(rootmnt);
2947     if (pwdmnt)
2948         mntput(pwdmnt);
2949 
2950     return new_ns;
2951 }
2952 
2953 /**
2954  * create_mnt_ns - creates a private namespace and adds a root filesystem
2955  * @mnt: pointer to the new root filesystem mountpoint
2956  */
2957 static struct mnt_namespace *create_mnt_ns(struct vfsmount *m)
2958 {
2959     struct mnt_namespace *new_ns = alloc_mnt_ns(&init_user_ns);
2960     if (!IS_ERR(new_ns)) {
2961         struct mount *mnt = real_mount(m);
2962         mnt->mnt_ns = new_ns;
2963         new_ns->root = mnt;
2964         new_ns->mounts++;
2965         list_add(&mnt->mnt_list, &new_ns->list);
2966     } else {
2967         mntput(m);
2968     }
2969     return new_ns;
2970 }
2971 
2972 struct dentry *mount_subtree(struct vfsmount *mnt, const char *name)
2973 {
2974     struct mnt_namespace *ns;
2975     struct super_block *s;
2976     struct path path;
2977     int err;
2978 
2979     ns = create_mnt_ns(mnt);
2980     if (IS_ERR(ns))
2981         return ERR_CAST(ns);
2982 
2983     err = vfs_path_lookup(mnt->mnt_root, mnt,
2984             name, LOOKUP_FOLLOW|LOOKUP_AUTOMOUNT, &path);
2985 
2986     put_mnt_ns(ns);
2987 
2988     if (err)
2989         return ERR_PTR(err);
2990 
2991     /* trade a vfsmount reference for active sb one */
2992     s = path.mnt->mnt_sb;
2993     atomic_inc(&s->s_active);
2994     mntput(path.mnt);
2995     /* lock the sucker */
2996     down_write(&s->s_umount);
2997     /* ... and return the root of (sub)tree on it */
2998     return path.dentry;
2999 }
3000 EXPORT_SYMBOL(mount_subtree);
3001 
3002 SYSCALL_DEFINE5(mount, char __user *, dev_name, char __user *, dir_name,
3003         char __user *, type, unsigned long, flags, void __user *, data)
3004 {
3005     int ret;
3006     char *kernel_type;
3007     char *kernel_dev;
3008     void *options;
3009 
3010     kernel_type = copy_mount_string(type);
3011     ret = PTR_ERR(kernel_type);
3012     if (IS_ERR(kernel_type))
3013         goto out_type;
3014 
3015     kernel_dev = copy_mount_string(dev_name);
3016     ret = PTR_ERR(kernel_dev);
3017     if (IS_ERR(kernel_dev))
3018         goto out_dev;
3019 
3020     options = copy_mount_options(data);
3021     ret = PTR_ERR(options);
3022     if (IS_ERR(options))
3023         goto out_data;
3024 
3025     ret = do_mount(kernel_dev, dir_name, kernel_type, flags, options);
3026 
3027     kfree(options);
3028 out_data:
3029     kfree(kernel_dev);
3030 out_dev:
3031     kfree(kernel_type);
3032 out_type:
3033     return ret;
3034 }
3035 
3036 /*
3037  * Return true if path is reachable from root
3038  *
3039  * namespace_sem or mount_lock is held
3040  */
3041 bool is_path_reachable(struct mount *mnt, struct dentry *dentry,
3042              const struct path *root)
3043 {
3044     while (&mnt->mnt != root->mnt && mnt_has_parent(mnt)) {
3045         dentry = mnt->mnt_mountpoint;
3046         mnt = mnt->mnt_parent;
3047     }
3048     return &mnt->mnt == root->mnt && is_subdir(dentry, root->dentry);
3049 }
3050 
3051 bool path_is_under(const struct path *path1, const struct path *path2)
3052 {
3053     bool res;
3054     read_seqlock_excl(&mount_lock);
3055     res = is_path_reachable(real_mount(path1->mnt), path1->dentry, path2);
3056     read_sequnlock_excl(&mount_lock);
3057     return res;
3058 }
3059 EXPORT_SYMBOL(path_is_under);
3060 
3061 /*
3062  * pivot_root Semantics:
3063  * Moves the root file system of the current process to the directory put_old,
3064  * makes new_root as the new root file system of the current process, and sets
3065  * root/cwd of all processes which had them on the current root to new_root.
3066  *
3067  * Restrictions:
3068  * The new_root and put_old must be directories, and  must not be on the
3069  * same file  system as the current process root. The put_old  must  be
3070  * underneath new_root,  i.e. adding a non-zero number of /.. to the string
3071  * pointed to by put_old must yield the same directory as new_root. No other
3072  * file system may be mounted on put_old. After all, new_root is a mountpoint.
3073  *
3074  * Also, the current root cannot be on the 'rootfs' (initial ramfs) filesystem.
3075  * See Documentation/filesystems/ramfs-rootfs-initramfs.txt for alternatives
3076  * in this situation.
3077  *
3078  * Notes:
3079  *  - we don't move root/cwd if they are not at the root (reason: if something
3080  *    cared enough to change them, it's probably wrong to force them elsewhere)
3081  *  - it's okay to pick a root that isn't the root of a file system, e.g.
3082  *    /nfs/my_root where /nfs is the mount point. It must be a mountpoint,
3083  *    though, so you may need to say mount --bind /nfs/my_root /nfs/my_root
3084  *    first.
3085  */
3086 SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
3087         const char __user *, put_old)
3088 {
3089     struct path new, old, parent_path, root_parent, root;
3090     struct mount *new_mnt, *root_mnt, *old_mnt;
3091     struct mountpoint *old_mp, *root_mp;
3092     int error;
3093 
3094     if (!may_mount())
3095         return -EPERM;
3096 
3097     error = user_path_dir(new_root, &new);
3098     if (error)
3099         goto out0;
3100 
3101     error = user_path_dir(put_old, &old);
3102     if (error)
3103         goto out1;
3104 
3105     error = security_sb_pivotroot(&old, &new);
3106     if (error)
3107         goto out2;
3108 
3109     get_fs_root(current->fs, &root);
3110     old_mp = lock_mount(&old);
3111     error = PTR_ERR(old_mp);
3112     if (IS_ERR(old_mp))
3113         goto out3;
3114 
3115     error = -EINVAL;
3116     new_mnt = real_mount(new.mnt);
3117     root_mnt = real_mount(root.mnt);
3118     old_mnt = real_mount(old.mnt);
3119     if (IS_MNT_SHARED(old_mnt) ||
3120         IS_MNT_SHARED(new_mnt->mnt_parent) ||
3121         IS_MNT_SHARED(root_mnt->mnt_parent))
3122         goto out4;
3123     if (!check_mnt(root_mnt) || !check_mnt(new_mnt))
3124         goto out4;
3125     if (new_mnt->mnt.mnt_flags & MNT_LOCKED)
3126         goto out4;
3127     error = -ENOENT;
3128     if (d_unlinked(new.dentry))
3129         goto out4;
3130     error = -EBUSY;
3131     if (new_mnt == root_mnt || old_mnt == root_mnt)
3132         goto out4; /* loop, on the same file system  */
3133     error = -EINVAL;
3134     if (root.mnt->mnt_root != root.dentry)
3135         goto out4; /* not a mountpoint */
3136     if (!mnt_has_parent(root_mnt))
3137         goto out4; /* not attached */
3138     root_mp = root_mnt->mnt_mp;
3139     if (new.mnt->mnt_root != new.dentry)
3140         goto out4; /* not a mountpoint */
3141     if (!mnt_has_parent(new_mnt))
3142         goto out4; /* not attached */
3143     /* make sure we can reach put_old from new_root */
3144     if (!is_path_reachable(old_mnt, old.dentry, &new))
3145         goto out4;
3146     /* make certain new is below the root */
3147     if (!is_path_reachable(new_mnt, new.dentry, &root))
3148         goto out4;
3149     root_mp->m_count++; /* pin it so it won't go away */
3150     lock_mount_hash();
3151     detach_mnt(new_mnt, &parent_path);
3152     detach_mnt(root_mnt, &root_parent);
3153     if (root_mnt->mnt.mnt_flags & MNT_LOCKED) {
3154         new_mnt->mnt.mnt_flags |= MNT_LOCKED;
3155         root_mnt->mnt.mnt_flags &= ~MNT_LOCKED;
3156     }
3157     /* mount old root on put_old */
3158     attach_mnt(root_mnt, old_mnt, old_mp);
3159     /* mount new_root on / */
3160     attach_mnt(new_mnt, real_mount(root_parent.mnt), root_mp);
3161     touch_mnt_namespace(current->nsproxy->mnt_ns);
3162     /* A moved mount should not expire automatically */
3163     list_del_init(&new_mnt->mnt_expire);
3164     put_mountpoint(root_mp);
3165     unlock_mount_hash();
3166     chroot_fs_refs(&root, &new);
3167     error = 0;
3168 out4:
3169     unlock_mount(old_mp);
3170     if (!error) {
3171         path_put(&root_parent);
3172         path_put(&parent_path);
3173     }
3174 out3:
3175     path_put(&root);
3176 out2:
3177     path_put(&old);
3178 out1:
3179     path_put(&new);
3180 out0:
3181     return error;
3182 }
3183 
3184 static void __init init_mount_tree(void)
3185 {
3186     struct vfsmount *mnt;
3187     struct mnt_namespace *ns;
3188     struct path root;
3189     struct file_system_type *type;
3190 
3191     type = get_fs_type("rootfs");
3192     if (!type)
3193         panic("Can't find rootfs type");
3194     mnt = vfs_kern_mount(type, 0, "rootfs", NULL);
3195     put_filesystem(type);
3196     if (IS_ERR(mnt))
3197         panic("Can't create rootfs");
3198 
3199     ns = create_mnt_ns(mnt);
3200     if (IS_ERR(ns))
3201         panic("Can't allocate initial namespace");
3202 
3203     init_task.nsproxy->mnt_ns = ns;
3204     get_mnt_ns(ns);
3205 
3206     root.mnt = mnt;
3207     root.dentry = mnt->mnt_root;
3208     mnt->mnt_flags |= MNT_LOCKED;
3209 
3210     set_fs_pwd(current->fs, &root);
3211     set_fs_root(current->fs, &root);
3212 }
3213 
3214 void __init mnt_init(void)
3215 {
3216     unsigned u;
3217     int err;
3218 
3219     mnt_cache = kmem_cache_create("mnt_cache", sizeof(struct mount),
3220             0, SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
3221 
3222     mount_hashtable = alloc_large_system_hash("Mount-cache",
3223                 sizeof(struct hlist_head),
3224                 mhash_entries, 19,
3225                 0,
3226                 &m_hash_shift, &m_hash_mask, 0, 0);
3227     mountpoint_hashtable = alloc_large_system_hash("Mountpoint-cache",
3228                 sizeof(struct hlist_head),
3229                 mphash_entries, 19,
3230                 0,
3231                 &mp_hash_shift, &mp_hash_mask, 0, 0);
3232 
3233     if (!mount_hashtable || !mountpoint_hashtable)
3234         panic("Failed to allocate mount hash table\n");
3235 
3236     for (u = 0; u <= m_hash_mask; u++)
3237         INIT_HLIST_HEAD(&mount_hashtable[u]);
3238     for (u = 0; u <= mp_hash_mask; u++)
3239         INIT_HLIST_HEAD(&mountpoint_hashtable[u]);
3240 
3241     kernfs_init();
3242 
3243     err = sysfs_init();
3244     if (err)
3245         printk(KERN_WARNING "%s: sysfs_init error: %d\n",
3246             __func__, err);
3247     fs_kobj = kobject_create_and_add("fs", NULL);
3248     if (!fs_kobj)
3249         printk(KERN_WARNING "%s: kobj create error\n", __func__);
3250     init_rootfs();
3251     init_mount_tree();
3252 }
3253 
3254 void put_mnt_ns(struct mnt_namespace *ns)
3255 {
3256     if (!atomic_dec_and_test(&ns->count))
3257         return;
3258     drop_collected_mounts(&ns->root->mnt);
3259     free_mnt_ns(ns);
3260 }
3261 
3262 struct vfsmount *kern_mount_data(struct file_system_type *type, void *data)
3263 {
3264     struct vfsmount *mnt;
3265     mnt = vfs_kern_mount(type, MS_KERNMOUNT, type->name, data);
3266     if (!IS_ERR(mnt)) {
3267         /*
3268          * it is a longterm mount, don't release mnt until
3269          * we unmount before file sys is unregistered
3270         */
3271         real_mount(mnt)->mnt_ns = MNT_NS_INTERNAL;
3272     }
3273     return mnt;
3274 }
3275 EXPORT_SYMBOL_GPL(kern_mount_data);
3276 
3277 void kern_unmount(struct vfsmount *mnt)
3278 {
3279     /* release long term mount so mount point can be released */
3280     if (!IS_ERR_OR_NULL(mnt)) {
3281         real_mount(mnt)->mnt_ns = NULL;
3282         synchronize_rcu();  /* yecchhh... */
3283         mntput(mnt);
3284     }
3285 }
3286 EXPORT_SYMBOL(kern_unmount);
3287 
3288 bool our_mnt(struct vfsmount *mnt)
3289 {
3290     return check_mnt(real_mount(mnt));
3291 }
3292 
3293 bool current_chrooted(void)
3294 {
3295     /* Does the current process have a non-standard root */
3296     struct path ns_root;
3297     struct path fs_root;
3298     bool chrooted;
3299 
3300     /* Find the namespace root */
3301     ns_root.mnt = &current->nsproxy->mnt_ns->root->mnt;
3302     ns_root.dentry = ns_root.mnt->mnt_root;
3303     path_get(&ns_root);
3304     while (d_mountpoint(ns_root.dentry) && follow_down_one(&ns_root))
3305         ;
3306 
3307     get_fs_root(current->fs, &fs_root);
3308 
3309     chrooted = !path_equal(&fs_root, &ns_root);
3310 
3311     path_put(&fs_root);
3312     path_put(&ns_root);
3313 
3314     return chrooted;
3315 }
3316 
3317 static bool mnt_already_visible(struct mnt_namespace *ns, struct vfsmount *new,
3318                 int *new_mnt_flags)
3319 {
3320     int new_flags = *new_mnt_flags;
3321     struct mount *mnt;
3322     bool visible = false;
3323 
3324     down_read(&namespace_sem);
3325     list_for_each_entry(mnt, &ns->list, mnt_list) {
3326         struct mount *child;
3327         int mnt_flags;
3328 
3329         if (mnt->mnt.mnt_sb->s_type != new->mnt_sb->s_type)
3330             continue;
3331 
3332         /* This mount is not fully visible if it's root directory
3333          * is not the root directory of the filesystem.
3334          */
3335         if (mnt->mnt.mnt_root != mnt->mnt.mnt_sb->s_root)
3336             continue;
3337 
3338         /* A local view of the mount flags */
3339         mnt_flags = mnt->mnt.mnt_flags;
3340 
3341         /* Don't miss readonly hidden in the superblock flags */
3342         if (mnt->mnt.mnt_sb->s_flags & MS_RDONLY)
3343             mnt_flags |= MNT_LOCK_READONLY;
3344 
3345         /* Verify the mount flags are equal to or more permissive
3346          * than the proposed new mount.
3347          */
3348         if ((mnt_flags & MNT_LOCK_READONLY) &&
3349             !(new_flags & MNT_READONLY))
3350             continue;
3351         if ((mnt_flags & MNT_LOCK_ATIME) &&
3352             ((mnt_flags & MNT_ATIME_MASK) != (new_flags & MNT_ATIME_MASK)))
3353             continue;
3354 
3355         /* This mount is not fully visible if there are any
3356          * locked child mounts that cover anything except for
3357          * empty directories.
3358          */
3359         list_for_each_entry(child, &mnt->mnt_mounts, mnt_child) {
3360             struct inode *inode = child->mnt_mountpoint->d_inode;
3361             /* Only worry about locked mounts */
3362             if (!(child->mnt.mnt_flags & MNT_LOCKED))
3363                 continue;
3364             /* Is the directory permanetly empty? */
3365             if (!is_empty_dir_inode(inode))
3366                 goto next;
3367         }
3368         /* Preserve the locked attributes */
3369         *new_mnt_flags |= mnt_flags & (MNT_LOCK_READONLY | \
3370                            MNT_LOCK_ATIME);
3371         visible = true;
3372         goto found;
3373     next:   ;
3374     }
3375 found:
3376     up_read(&namespace_sem);
3377     return visible;
3378 }
3379 
3380 static bool mount_too_revealing(struct vfsmount *mnt, int *new_mnt_flags)
3381 {
3382     const unsigned long required_iflags = SB_I_NOEXEC | SB_I_NODEV;
3383     struct mnt_namespace *ns = current->nsproxy->mnt_ns;
3384     unsigned long s_iflags;
3385 
3386     if (ns->user_ns == &init_user_ns)
3387         return false;
3388 
3389     /* Can this filesystem be too revealing? */
3390     s_iflags = mnt->mnt_sb->s_iflags;
3391     if (!(s_iflags & SB_I_USERNS_VISIBLE))
3392         return false;
3393 
3394     if ((s_iflags & required_iflags) != required_iflags) {
3395         WARN_ONCE(1, "Expected s_iflags to contain 0x%lx\n",
3396               required_iflags);
3397         return true;
3398     }
3399 
3400     return !mnt_already_visible(ns, mnt, new_mnt_flags);
3401 }
3402 
3403 bool mnt_may_suid(struct vfsmount *mnt)
3404 {
3405     /*
3406      * Foreign mounts (accessed via fchdir or through /proc
3407      * symlinks) are always treated as if they are nosuid.  This
3408      * prevents namespaces from trusting potentially unsafe
3409      * suid/sgid bits, file caps, or security labels that originate
3410      * in other namespaces.
3411      */
3412     return !(mnt->mnt_flags & MNT_NOSUID) && check_mnt(real_mount(mnt)) &&
3413            current_in_userns(mnt->mnt_sb->s_user_ns);
3414 }
3415 
3416 static struct ns_common *mntns_get(struct task_struct *task)
3417 {
3418     struct ns_common *ns = NULL;
3419     struct nsproxy *nsproxy;
3420 
3421     task_lock(task);
3422     nsproxy = task->nsproxy;
3423     if (nsproxy) {
3424         ns = &nsproxy->mnt_ns->ns;
3425         get_mnt_ns(to_mnt_ns(ns));
3426     }
3427     task_unlock(task);
3428 
3429     return ns;
3430 }
3431 
3432 static void mntns_put(struct ns_common *ns)
3433 {
3434     put_mnt_ns(to_mnt_ns(ns));
3435 }
3436 
3437 static int mntns_install(struct nsproxy *nsproxy, struct ns_common *ns)
3438 {
3439     struct fs_struct *fs = current->fs;
3440     struct mnt_namespace *mnt_ns = to_mnt_ns(ns);
3441     struct path root;
3442 
3443     if (!ns_capable(mnt_ns->user_ns, CAP_SYS_ADMIN) ||
3444         !ns_capable(current_user_ns(), CAP_SYS_CHROOT) ||
3445         !ns_capable(current_user_ns(), CAP_SYS_ADMIN))
3446         return -EPERM;
3447 
3448     if (fs->users != 1)
3449         return -EINVAL;
3450 
3451     get_mnt_ns(mnt_ns);
3452     put_mnt_ns(nsproxy->mnt_ns);
3453     nsproxy->mnt_ns = mnt_ns;
3454 
3455     /* Find the root */
3456     root.mnt    = &mnt_ns->root->mnt;
3457     root.dentry = mnt_ns->root->mnt.mnt_root;
3458     path_get(&root);
3459     while(d_mountpoint(root.dentry) && follow_down_one(&root))
3460         ;
3461 
3462     /* Update the pwd and root */
3463     set_fs_pwd(fs, &root);
3464     set_fs_root(fs, &root);
3465 
3466     path_put(&root);
3467     return 0;
3468 }
3469 
3470 static struct user_namespace *mntns_owner(struct ns_common *ns)
3471 {
3472     return to_mnt_ns(ns)->user_ns;
3473 }
3474 
3475 const struct proc_ns_operations mntns_operations = {
3476     .name       = "mnt",
3477     .type       = CLONE_NEWNS,
3478     .get        = mntns_get,
3479     .put        = mntns_put,
3480     .install    = mntns_install,
3481     .owner      = mntns_owner,
3482 };