OSCL-LXR linux-6.0.1/​fs/​proc/​proc_sysctl.c	Source navigation Diff markup Identifier search General search
	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 // SPDX-License-Identifier: GPL-2.0
 /*
  * /proc/sys support
  */
 #include <linux/init.h>
 #include <linux/sysctl.h>
 #include <linux/poll.h>
 #include <linux/proc_fs.h>
 #include <linux/printk.h>
 #include <linux/security.h>
 #include <linux/sched.h>
 #include <linux/cred.h>
 #include <linux/namei.h>
 #include <linux/mm.h>
 #include <linux/uio.h>
 #include <linux/module.h>
 #include <linux/bpf-cgroup.h>
 #include <linux/mount.h>
 #include <linux/kmemleak.h>
 #include "internal.h"
 
 #define list_for_each_table_entry(entry, table) \
     for ((entry) = (table); (entry)->procname; (entry)++)
 
 static const struct dentry_operations proc_sys_dentry_operations;
 static const struct file_operations proc_sys_file_operations;
 static const struct inode_operations proc_sys_inode_operations;
 static const struct file_operations proc_sys_dir_file_operations;
 static const struct inode_operations proc_sys_dir_operations;
 
 /* shared constants to be used in various sysctls */
 const int sysctl_vals[] = { 0, 1, 2, 3, 4, 100, 200, 1000, 3000, INT_MAX, 65535, -1 };
 EXPORT_SYMBOL(sysctl_vals);
 
 const unsigned long sysctl_long_vals[] = { 0, 1, LONG_MAX };
 EXPORT_SYMBOL_GPL(sysctl_long_vals);
 
 /* Support for permanently empty directories */
 
 struct ctl_table sysctl_mount_point[] = {
     { }
 };
 
 /**
  * register_sysctl_mount_point() - registers a sysctl mount point
  * @path: path for the mount point
  *
  * Used to create a permanently empty directory to serve as mount point.
  * There are some subtle but important permission checks this allows in the
  * case of unprivileged mounts.
  */
 struct ctl_table_header *register_sysctl_mount_point(const char *path)
 {
     return register_sysctl(path, sysctl_mount_point);
 }
 EXPORT_SYMBOL(register_sysctl_mount_point);
 
 static bool is_empty_dir(struct ctl_table_header *head)
 {
     return head->ctl_table[0].child == sysctl_mount_point;
 }
 
 static void set_empty_dir(struct ctl_dir *dir)
 {
     dir->header.ctl_table[0].child = sysctl_mount_point;
 }
 
 static void clear_empty_dir(struct ctl_dir *dir)
 
 {
     dir->header.ctl_table[0].child = NULL;
 }
 
 void proc_sys_poll_notify(struct ctl_table_poll *poll)
 {
     if (!poll)
         return;
 
     atomic_inc(&poll->event);
     wake_up_interruptible(&poll->wait);
 }
 
 static struct ctl_table root_table[] = {
     {
         .procname = "",
         .mode = S_IFDIR|S_IRUGO|S_IXUGO,
     },
     { }
 };
 static struct ctl_table_root sysctl_table_root = {
     .default_set.dir.header = {
         {{.count = 1,
           .nreg = 1,
           .ctl_table = root_table }},
         .ctl_table_arg = root_table,
         .root = &sysctl_table_root,
         .set = &sysctl_table_root.default_set,
     },
 };
 
 static DEFINE_SPINLOCK(sysctl_lock);
 
 static void drop_sysctl_table(struct ctl_table_header *header);
 static int sysctl_follow_link(struct ctl_table_header **phead,
     struct ctl_table **pentry);
 static int insert_links(struct ctl_table_header *head);
 static void put_links(struct ctl_table_header *header);
 
 static void sysctl_print_dir(struct ctl_dir *dir)
 {
     if (dir->header.parent)
         sysctl_print_dir(dir->header.parent);
     pr_cont("%s/", dir->header.ctl_table[0].procname);
 }
 
 static int namecmp(const char *name1, int len1, const char *name2, int len2)
 {
     int cmp;
 
     cmp = memcmp(name1, name2, min(len1, len2));
     if (cmp == 0)
         cmp = len1 - len2;
     return cmp;
 }
 
 /* Called under sysctl_lock */
 static struct ctl_table *find_entry(struct ctl_table_header **phead,
     struct ctl_dir *dir, const char *name, int namelen)
 {
     struct ctl_table_header *head;
     struct ctl_table *entry;
     struct rb_node *node = dir->root.rb_node;
 
     while (node)
     {
         struct ctl_node *ctl_node;
         const char *procname;
         int cmp;
 
         ctl_node = rb_entry(node, struct ctl_node, node);
         head = ctl_node->header;
         entry = &head->ctl_table[ctl_node - head->node];
         procname = entry->procname;
 
         cmp = namecmp(name, namelen, procname, strlen(procname));
         if (cmp < 0)
             node = node->rb_left;
         else if (cmp > 0)
             node = node->rb_right;
         else {
             *phead = head;
             return entry;
         }
     }
     return NULL;
 }
 
 static int insert_entry(struct ctl_table_header *head, struct ctl_table *entry)
 {
     struct rb_node *node = &head->node[entry - head->ctl_table].node;
     struct rb_node **p = &head->parent->root.rb_node;
     struct rb_node *parent = NULL;
     const char *name = entry->procname;
     int namelen = strlen(name);
 
     while (*p) {
         struct ctl_table_header *parent_head;
         struct ctl_table *parent_entry;
         struct ctl_node *parent_node;
         const char *parent_name;
         int cmp;
 
         parent = *p;
         parent_node = rb_entry(parent, struct ctl_node, node);
         parent_head = parent_node->header;
         parent_entry = &parent_head->ctl_table[parent_node - parent_head->node];
         parent_name = parent_entry->procname;
 
         cmp = namecmp(name, namelen, parent_name, strlen(parent_name));
         if (cmp < 0)
             p = &(*p)->rb_left;
         else if (cmp > 0)
             p = &(*p)->rb_right;
         else {
             pr_err("sysctl duplicate entry: ");
             sysctl_print_dir(head->parent);
             pr_cont("%s\n", entry->procname);
             return -EEXIST;
         }
     }
 
     rb_link_node(node, parent, p);
     rb_insert_color(node, &head->parent->root);
     return 0;
 }
 
 static void erase_entry(struct ctl_table_header *head, struct ctl_table *entry)
 {
     struct rb_node *node = &head->node[entry - head->ctl_table].node;
 
     rb_erase(node, &head->parent->root);
 }
 
 static void init_header(struct ctl_table_header *head,
     struct ctl_table_root *root, struct ctl_table_set *set,
     struct ctl_node *node, struct ctl_table *table)
 {
     head->ctl_table = table;
     head->ctl_table_arg = table;
     head->used = 0;
     head->count = 1;
     head->nreg = 1;
     head->unregistering = NULL;
     head->root = root;
     head->set = set;
     head->parent = NULL;
     head->node = node;
     INIT_HLIST_HEAD(&head->inodes);
     if (node) {
         struct ctl_table *entry;
 
         list_for_each_table_entry(entry, table) {
             node->header = head;
             node++;
         }
     }
 }
 
 static void erase_header(struct ctl_table_header *head)
 {
     struct ctl_table *entry;
 
     list_for_each_table_entry(entry, head->ctl_table)
         erase_entry(head, entry);
 }
 
 static int insert_header(struct ctl_dir *dir, struct ctl_table_header *header)
 {
     struct ctl_table *entry;
     int err;
 
     /* Is this a permanently empty directory? */
     if (is_empty_dir(&dir->header))
         return -EROFS;
 
     /* Am I creating a permanently empty directory? */
     if (header->ctl_table == sysctl_mount_point) {
         if (!RB_EMPTY_ROOT(&dir->root))
             return -EINVAL;
         set_empty_dir(dir);
     }
 
     dir->header.nreg++;
     header->parent = dir;
     err = insert_links(header);
     if (err)
         goto fail_links;
     list_for_each_table_entry(entry, header->ctl_table) {
         err = insert_entry(header, entry);
         if (err)
             goto fail;
     }
     return 0;
 fail:
     erase_header(header);
     put_links(header);
 fail_links:
     if (header->ctl_table == sysctl_mount_point)
         clear_empty_dir(dir);
     header->parent = NULL;
     drop_sysctl_table(&dir->header);
     return err;
 }
 
 /* called under sysctl_lock */
 static int use_table(struct ctl_table_header *p)
 {
     if (unlikely(p->unregistering))
         return 0;
     p->used++;
     return 1;
 }
 
 /* called under sysctl_lock */
 static void unuse_table(struct ctl_table_header *p)
 {
     if (!--p->used)
         if (unlikely(p->unregistering))
             complete(p->unregistering);
 }
 
 static void proc_sys_invalidate_dcache(struct ctl_table_header *head)
 {
     proc_invalidate_siblings_dcache(&head->inodes, &sysctl_lock);
 }
 
 /* called under sysctl_lock, will reacquire if has to wait */
 static void start_unregistering(struct ctl_table_header *p)
 {
     /*
      * if p->used is 0, nobody will ever touch that entry again;
      * we'll eliminate all paths to it before dropping sysctl_lock
      */
     if (unlikely(p->used)) {
         struct completion wait;
         init_completion(&wait);
         p->unregistering = &wait;
         spin_unlock(&sysctl_lock);
         wait_for_completion(&wait);
     } else {
         /* anything non-NULL; we'll never dereference it */
         p->unregistering = ERR_PTR(-EINVAL);
         spin_unlock(&sysctl_lock);
     }
     /*
      * Invalidate dentries for unregistered sysctls: namespaced sysctls
      * can have duplicate names and contaminate dcache very badly.
      */
     proc_sys_invalidate_dcache(p);
     /*
      * do not remove from the list until nobody holds it; walking the
      * list in do_sysctl() relies on that.
      */
     spin_lock(&sysctl_lock);
     erase_header(p);
 }
 
 static struct ctl_table_header *sysctl_head_grab(struct ctl_table_header *head)
 {
     BUG_ON(!head);
     spin_lock(&sysctl_lock);
     if (!use_table(head))
         head = ERR_PTR(-ENOENT);
     spin_unlock(&sysctl_lock);
     return head;
 }
 
 static void sysctl_head_finish(struct ctl_table_header *head)
 {
     if (!head)
         return;
     spin_lock(&sysctl_lock);
     unuse_table(head);
     spin_unlock(&sysctl_lock);
 }
 
 static struct ctl_table_set *
 lookup_header_set(struct ctl_table_root *root)
 {
     struct ctl_table_set *set = &root->default_set;
     if (root->lookup)
         set = root->lookup(root);
     return set;
 }
 
 static struct ctl_table *lookup_entry(struct ctl_table_header **phead,
                       struct ctl_dir *dir,
                       const char *name, int namelen)
 {
     struct ctl_table_header *head;
     struct ctl_table *entry;
 
     spin_lock(&sysctl_lock);
     entry = find_entry(&head, dir, name, namelen);
     if (entry && use_table(head))
         *phead = head;
     else
         entry = NULL;
     spin_unlock(&sysctl_lock);
     return entry;
 }
 
 static struct ctl_node *first_usable_entry(struct rb_node *node)
 {
     struct ctl_node *ctl_node;
 
     for (;node; node = rb_next(node)) {
         ctl_node = rb_entry(node, struct ctl_node, node);
         if (use_table(ctl_node->header))
             return ctl_node;
     }
     return NULL;
 }
 
 static void first_entry(struct ctl_dir *dir,
     struct ctl_table_header **phead, struct ctl_table **pentry)
 {
     struct ctl_table_header *head = NULL;
     struct ctl_table *entry = NULL;
     struct ctl_node *ctl_node;
 
     spin_lock(&sysctl_lock);
     ctl_node = first_usable_entry(rb_first(&dir->root));
     spin_unlock(&sysctl_lock);
     if (ctl_node) {
         head = ctl_node->header;
         entry = &head->ctl_table[ctl_node - head->node];
     }
     *phead = head;
     *pentry = entry;
 }
 
 static void next_entry(struct ctl_table_header **phead, struct ctl_table **pentry)
 {
     struct ctl_table_header *head = *phead;
     struct ctl_table *entry = *pentry;
     struct ctl_node *ctl_node = &head->node[entry - head->ctl_table];
 
     spin_lock(&sysctl_lock);
     unuse_table(head);
 
     ctl_node = first_usable_entry(rb_next(&ctl_node->node));
     spin_unlock(&sysctl_lock);
     head = NULL;
     if (ctl_node) {
         head = ctl_node->header;
         entry = &head->ctl_table[ctl_node - head->node];
     }
     *phead = head;
     *pentry = entry;
 }
 
 /*
  * sysctl_perm does NOT grant the superuser all rights automatically, because
  * some sysctl variables are readonly even to root.
  */
 
 static int test_perm(int mode, int op)
 {
     if (uid_eq(current_euid(), GLOBAL_ROOT_UID))
         mode >>= 6;
     else if (in_egroup_p(GLOBAL_ROOT_GID))
         mode >>= 3;
     if ((op & ~mode & (MAY_READ|MAY_WRITE|MAY_EXEC)) == 0)
         return 0;
     return -EACCES;
 }
 
 static int sysctl_perm(struct ctl_table_header *head, struct ctl_table *table, int op)
 {
     struct ctl_table_root *root = head->root;
     int mode;
 
     if (root->permissions)
         mode = root->permissions(head, table);
     else
         mode = table->mode;
 
     return test_perm(mode, op);
 }
 
 static struct inode *proc_sys_make_inode(struct super_block *sb,
         struct ctl_table_header *head, struct ctl_table *table)
 {
     struct ctl_table_root *root = head->root;
     struct inode *inode;
     struct proc_inode *ei;
 
     inode = new_inode(sb);
     if (!inode)
         return ERR_PTR(-ENOMEM);
 
     inode->i_ino = get_next_ino();
 
     ei = PROC_I(inode);
 
     spin_lock(&sysctl_lock);
     if (unlikely(head->unregistering)) {
         spin_unlock(&sysctl_lock);
         iput(inode);
         return ERR_PTR(-ENOENT);
     }
     ei->sysctl = head;
     ei->sysctl_entry = table;
     hlist_add_head_rcu(&ei->sibling_inodes, &head->inodes);
     head->count++;
     spin_unlock(&sysctl_lock);
 
     inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
     inode->i_mode = table->mode;
     if (!S_ISDIR(table->mode)) {
         inode->i_mode |= S_IFREG;
         inode->i_op = &proc_sys_inode_operations;
         inode->i_fop = &proc_sys_file_operations;
     } else {
         inode->i_mode |= S_IFDIR;
         inode->i_op = &proc_sys_dir_operations;
         inode->i_fop = &proc_sys_dir_file_operations;
         if (is_empty_dir(head))
             make_empty_dir_inode(inode);
     }
 
     if (root->set_ownership)
         root->set_ownership(head, table, &inode->i_uid, &inode->i_gid);
     else {
         inode->i_uid = GLOBAL_ROOT_UID;
         inode->i_gid = GLOBAL_ROOT_GID;
     }
 
     return inode;
 }
 
 void proc_sys_evict_inode(struct inode *inode, struct ctl_table_header *head)
 {
     spin_lock(&sysctl_lock);
     hlist_del_init_rcu(&PROC_I(inode)->sibling_inodes);
     if (!--head->count)
         kfree_rcu(head, rcu);
     spin_unlock(&sysctl_lock);
 }
 
 static struct ctl_table_header *grab_header(struct inode *inode)
 {
     struct ctl_table_header *head = PROC_I(inode)->sysctl;
     if (!head)
         head = &sysctl_table_root.default_set.dir.header;
     return sysctl_head_grab(head);
 }
 
 static struct dentry *proc_sys_lookup(struct inode *dir, struct dentry *dentry,
                     unsigned int flags)
 {
     struct ctl_table_header *head = grab_header(dir);
     struct ctl_table_header *h = NULL;
     const struct qstr *name = &dentry->d_name;
     struct ctl_table *p;
     struct inode *inode;
     struct dentry *err = ERR_PTR(-ENOENT);
     struct ctl_dir *ctl_dir;
     int ret;
 
     if (IS_ERR(head))
         return ERR_CAST(head);
 
     ctl_dir = container_of(head, struct ctl_dir, header);
 
     p = lookup_entry(&h, ctl_dir, name->name, name->len);
     if (!p)
         goto out;
 
     if (S_ISLNK(p->mode)) {
         ret = sysctl_follow_link(&h, &p);
         err = ERR_PTR(ret);
         if (ret)
             goto out;
     }
 
     inode = proc_sys_make_inode(dir->i_sb, h ? h : head, p);
     if (IS_ERR(inode)) {
         err = ERR_CAST(inode);
         goto out;
     }
 
     d_set_d_op(dentry, &proc_sys_dentry_operations);
     err = d_splice_alias(inode, dentry);
 
 out:
     if (h)
         sysctl_head_finish(h);
     sysctl_head_finish(head);
     return err;
 }
 
 static ssize_t proc_sys_call_handler(struct kiocb *iocb, struct iov_iter *iter,
         int write)
 {
     struct inode *inode = file_inode(iocb->ki_filp);
     struct ctl_table_header *head = grab_header(inode);
     struct ctl_table *table = PROC_I(inode)->sysctl_entry;
     size_t count = iov_iter_count(iter);
     char *kbuf;
     ssize_t error;
 
     if (IS_ERR(head))
         return PTR_ERR(head);
 
     /*
      * At this point we know that the sysctl was not unregistered
      * and won't be until we finish.
      */
     error = -EPERM;
     if (sysctl_perm(head, table, write ? MAY_WRITE : MAY_READ))
         goto out;
 
     /* if that can happen at all, it should be -EINVAL, not -EISDIR */
     error = -EINVAL;
     if (!table->proc_handler)
         goto out;
 
     /* don't even try if the size is too large */
     error = -ENOMEM;
     if (count >= KMALLOC_MAX_SIZE)
         goto out;
     kbuf = kvzalloc(count + 1, GFP_KERNEL);
     if (!kbuf)
         goto out;
 
     if (write) {
         error = -EFAULT;
         if (!copy_from_iter_full(kbuf, count, iter))
             goto out_free_buf;
         kbuf[count] = '\0';
     }
 
     error = BPF_CGROUP_RUN_PROG_SYSCTL(head, table, write, &kbuf, &count,
                        &iocb->ki_pos);
     if (error)
         goto out_free_buf;
 
     /* careful: calling conventions are nasty here */
     error = table->proc_handler(table, write, kbuf, &count, &iocb->ki_pos);
     if (error)
         goto out_free_buf;
 
     if (!write) {
         error = -EFAULT;
         if (copy_to_iter(kbuf, count, iter) < count)
             goto out_free_buf;
     }
 
     error = count;
 out_free_buf:
     kvfree(kbuf);
 out:
     sysctl_head_finish(head);
 
     return error;
 }
 
 static ssize_t proc_sys_read(struct kiocb *iocb, struct iov_iter *iter)
 {
     return proc_sys_call_handler(iocb, iter, 0);
 }
 
 static ssize_t proc_sys_write(struct kiocb *iocb, struct iov_iter *iter)
 {
     return proc_sys_call_handler(iocb, iter, 1);
 }
 
 static int proc_sys_open(struct inode *inode, struct file *filp)
 {
     struct ctl_table_header *head = grab_header(inode);
     struct ctl_table *table = PROC_I(inode)->sysctl_entry;
 
     /* sysctl was unregistered */
     if (IS_ERR(head))
         return PTR_ERR(head);
 
     if (table->poll)
         filp->private_data = proc_sys_poll_event(table->poll);
 
     sysctl_head_finish(head);
 
     return 0;
 }
 
 static __poll_t proc_sys_poll(struct file *filp, poll_table *wait)
 {
     struct inode *inode = file_inode(filp);
     struct ctl_table_header *head = grab_header(inode);
     struct ctl_table *table = PROC_I(inode)->sysctl_entry;
     __poll_t ret = DEFAULT_POLLMASK;
     unsigned long event;
 
     /* sysctl was unregistered */
     if (IS_ERR(head))
         return EPOLLERR | EPOLLHUP;
 
     if (!table->proc_handler)
         goto out;
 
     if (!table->poll)
         goto out;
 
     event = (unsigned long)filp->private_data;
     poll_wait(filp, &table->poll->wait, wait);
 
     if (event != atomic_read(&table->poll->event)) {
         filp->private_data = proc_sys_poll_event(table->poll);
         ret = EPOLLIN | EPOLLRDNORM | EPOLLERR | EPOLLPRI;
     }
 
 out:
     sysctl_head_finish(head);
 
     return ret;
 }
 
 static bool proc_sys_fill_cache(struct file *file,
                 struct dir_context *ctx,
                 struct ctl_table_header *head,
                 struct ctl_table *table)
 {
     struct dentry *child, *dir = file->f_path.dentry;
     struct inode *inode;
     struct qstr qname;
     ino_t ino = 0;
     unsigned type = DT_UNKNOWN;
 
     qname.name = table->procname;
     qname.len  = strlen(table->procname);
     qname.hash = full_name_hash(dir, qname.name, qname.len);
 
     child = d_lookup(dir, &qname);
     if (!child) {
         DECLARE_WAIT_QUEUE_HEAD_ONSTACK(wq);
         child = d_alloc_parallel(dir, &qname, &wq);
         if (IS_ERR(child))
             return false;
         if (d_in_lookup(child)) {
             struct dentry *res;
             inode = proc_sys_make_inode(dir->d_sb, head, table);
             if (IS_ERR(inode)) {
                 d_lookup_done(child);
                 dput(child);
                 return false;
             }
             d_set_d_op(child, &proc_sys_dentry_operations);
             res = d_splice_alias(inode, child);
             d_lookup_done(child);
             if (unlikely(res)) {
                 if (IS_ERR(res)) {
                     dput(child);
                     return false;
                 }
                 dput(child);
                 child = res;
             }
         }
     }
     inode = d_inode(child);
     ino  = inode->i_ino;
     type = inode->i_mode >> 12;
     dput(child);
     return dir_emit(ctx, qname.name, qname.len, ino, type);
 }
 
 static bool proc_sys_link_fill_cache(struct file *file,
                     struct dir_context *ctx,
                     struct ctl_table_header *head,
                     struct ctl_table *table)
 {
     bool ret = true;
 
     head = sysctl_head_grab(head);
     if (IS_ERR(head))
         return false;
 
     /* It is not an error if we can not follow the link ignore it */
     if (sysctl_follow_link(&head, &table))
         goto out;
 
     ret = proc_sys_fill_cache(file, ctx, head, table);
 out:
     sysctl_head_finish(head);
     return ret;
 }
 
 static int scan(struct ctl_table_header *head, struct ctl_table *table,
         unsigned long *pos, struct file *file,
         struct dir_context *ctx)
 {
     bool res;
 
     if ((*pos)++ < ctx->pos)
         return true;
 
     if (unlikely(S_ISLNK(table->mode)))
         res = proc_sys_link_fill_cache(file, ctx, head, table);
     else
         res = proc_sys_fill_cache(file, ctx, head, table);
 
     if (res)
         ctx->pos = *pos;
 
     return res;
 }
 
 static int proc_sys_readdir(struct file *file, struct dir_context *ctx)
 {
     struct ctl_table_header *head = grab_header(file_inode(file));
     struct ctl_table_header *h = NULL;
     struct ctl_table *entry;
     struct ctl_dir *ctl_dir;
     unsigned long pos;
 
     if (IS_ERR(head))
         return PTR_ERR(head);
 
     ctl_dir = container_of(head, struct ctl_dir, header);
 
     if (!dir_emit_dots(file, ctx))
         goto out;
 
     pos = 2;
 
     for (first_entry(ctl_dir, &h, &entry); h; next_entry(&h, &entry)) {
         if (!scan(h, entry, &pos, file, ctx)) {
             sysctl_head_finish(h);
             break;
         }
     }
 out:
     sysctl_head_finish(head);
     return 0;
 }
 
 static int proc_sys_permission(struct user_namespace *mnt_userns,
                    struct inode *inode, int mask)
 {
     /*
      * sysctl entries that are not writeable,
      * are _NOT_ writeable, capabilities or not.
      */
     struct ctl_table_header *head;
     struct ctl_table *table;
     int error;
 
     /* Executable files are not allowed under /proc/sys/ */
     if ((mask & MAY_EXEC) && S_ISREG(inode->i_mode))
         return -EACCES;
 
     head = grab_header(inode);
     if (IS_ERR(head))
         return PTR_ERR(head);
 
     table = PROC_I(inode)->sysctl_entry;
     if (!table) /* global root - r-xr-xr-x */
         error = mask & MAY_WRITE ? -EACCES : 0;
     else /* Use the permissions on the sysctl table entry */
         error = sysctl_perm(head, table, mask & ~MAY_NOT_BLOCK);
 
     sysctl_head_finish(head);
     return error;
 }
 
 static int proc_sys_setattr(struct user_namespace *mnt_userns,
                 struct dentry *dentry, struct iattr *attr)
 {
     struct inode *inode = d_inode(dentry);
     int error;
 
     if (attr->ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID))
         return -EPERM;
 
     error = setattr_prepare(&init_user_ns, dentry, attr);
     if (error)
         return error;
 
     setattr_copy(&init_user_ns, inode, attr);
     mark_inode_dirty(inode);
     return 0;
 }
 
 static int proc_sys_getattr(struct user_namespace *mnt_userns,
                 const struct path *path, struct kstat *stat,
                 u32 request_mask, unsigned int query_flags)
 {
     struct inode *inode = d_inode(path->dentry);
     struct ctl_table_header *head = grab_header(inode);
     struct ctl_table *table = PROC_I(inode)->sysctl_entry;
 
     if (IS_ERR(head))
         return PTR_ERR(head);
 
     generic_fillattr(&init_user_ns, inode, stat);
     if (table)
         stat->mode = (stat->mode & S_IFMT) | table->mode;
 
     sysctl_head_finish(head);
     return 0;
 }
 
 static const struct file_operations proc_sys_file_operations = {
     .open       = proc_sys_open,
     .poll       = proc_sys_poll,
     .read_iter  = proc_sys_read,
     .write_iter = proc_sys_write,
     .splice_read    = generic_file_splice_read,
     .splice_write   = iter_file_splice_write,
     .llseek     = default_llseek,
 };
 
 static const struct file_operations proc_sys_dir_file_operations = {
     .read       = generic_read_dir,
     .iterate_shared = proc_sys_readdir,
     .llseek     = generic_file_llseek,
 };
 
 static const struct inode_operations proc_sys_inode_operations = {
     .permission = proc_sys_permission,
     .setattr    = proc_sys_setattr,
     .getattr    = proc_sys_getattr,
 };
 
 static const struct inode_operations proc_sys_dir_operations = {
     .lookup     = proc_sys_lookup,
     .permission = proc_sys_permission,
     .setattr    = proc_sys_setattr,
     .getattr    = proc_sys_getattr,
 };
 
 static int proc_sys_revalidate(struct dentry *dentry, unsigned int flags)
 {
     if (flags & LOOKUP_RCU)
         return -ECHILD;
     return !PROC_I(d_inode(dentry))->sysctl->unregistering;
 }
 
 static int proc_sys_delete(const struct dentry *dentry)
 {
     return !!PROC_I(d_inode(dentry))->sysctl->unregistering;
 }
 
 static int sysctl_is_seen(struct ctl_table_header *p)
 {
     struct ctl_table_set *set = p->set;
     int res;
     spin_lock(&sysctl_lock);
     if (p->unregistering)
         res = 0;
     else if (!set->is_seen)
         res = 1;
     else
         res = set->is_seen(set);
     spin_unlock(&sysctl_lock);
     return res;
 }
 
 static int proc_sys_compare(const struct dentry *dentry,
         unsigned int len, const char *str, const struct qstr *name)
 {
     struct ctl_table_header *head;
     struct inode *inode;
 
     /* Although proc doesn't have negative dentries, rcu-walk means
      * that inode here can be NULL */
     /* AV: can it, indeed? */
     inode = d_inode_rcu(dentry);
     if (!inode)
         return 1;
     if (name->len != len)
         return 1;
     if (memcmp(name->name, str, len))
         return 1;
     head = rcu_dereference(PROC_I(inode)->sysctl);
     return !head || !sysctl_is_seen(head);
 }
 
 static const struct dentry_operations proc_sys_dentry_operations = {
     .d_revalidate   = proc_sys_revalidate,
     .d_delete   = proc_sys_delete,
     .d_compare  = proc_sys_compare,
 };
 
 static struct ctl_dir *find_subdir(struct ctl_dir *dir,
                    const char *name, int namelen)
 {
     struct ctl_table_header *head;
     struct ctl_table *entry;
 
     entry = find_entry(&head, dir, name, namelen);
     if (!entry)
         return ERR_PTR(-ENOENT);
     if (!S_ISDIR(entry->mode))
         return ERR_PTR(-ENOTDIR);
     return container_of(head, struct ctl_dir, header);
 }
 
 static struct ctl_dir *new_dir(struct ctl_table_set *set,
                    const char *name, int namelen)
 {
     struct ctl_table *table;
     struct ctl_dir *new;
     struct ctl_node *node;
     char *new_name;
 
     new = kzalloc(sizeof(*new) + sizeof(struct ctl_node) +
               sizeof(struct ctl_table)*2 +  namelen + 1,
               GFP_KERNEL);
     if (!new)
         return NULL;
 
     node = (struct ctl_node *)(new + 1);
     table = (struct ctl_table *)(node + 1);
     new_name = (char *)(table + 2);
     memcpy(new_name, name, namelen);
     table[0].procname = new_name;
     table[0].mode = S_IFDIR|S_IRUGO|S_IXUGO;
     init_header(&new->header, set->dir.header.root, set, node, table);
 
     return new;
 }
 
 /**
  * get_subdir - find or create a subdir with the specified name.
  * @dir:  Directory to create the subdirectory in
  * @name: The name of the subdirectory to find or create
  * @namelen: The length of name
  *
  * Takes a directory with an elevated reference count so we know that
  * if we drop the lock the directory will not go away.  Upon success
  * the reference is moved from @dir to the returned subdirectory.
  * Upon error an error code is returned and the reference on @dir is
  * simply dropped.
  */
 static struct ctl_dir *get_subdir(struct ctl_dir *dir,
                   const char *name, int namelen)
 {
     struct ctl_table_set *set = dir->header.set;
     struct ctl_dir *subdir, *new = NULL;
     int err;
 
     spin_lock(&sysctl_lock);
     subdir = find_subdir(dir, name, namelen);
     if (!IS_ERR(subdir))
         goto found;
     if (PTR_ERR(subdir) != -ENOENT)
         goto failed;
 
     spin_unlock(&sysctl_lock);
     new = new_dir(set, name, namelen);
     spin_lock(&sysctl_lock);
     subdir = ERR_PTR(-ENOMEM);
     if (!new)
         goto failed;
 
     /* Was the subdir added while we dropped the lock? */
     subdir = find_subdir(dir, name, namelen);
     if (!IS_ERR(subdir))
         goto found;
     if (PTR_ERR(subdir) != -ENOENT)
         goto failed;
 
     /* Nope.  Use the our freshly made directory entry. */
     err = insert_header(dir, &new->header);
     subdir = ERR_PTR(err);
     if (err)
         goto failed;
     subdir = new;
 found:
     subdir->header.nreg++;
 failed:
     if (IS_ERR(subdir)) {
         pr_err("sysctl could not get directory: ");
         sysctl_print_dir(dir);
         pr_cont("%*.*s %ld\n", namelen, namelen, name,
             PTR_ERR(subdir));
     }
     drop_sysctl_table(&dir->header);
     if (new)
         drop_sysctl_table(&new->header);
     spin_unlock(&sysctl_lock);
     return subdir;
 }
 
 static struct ctl_dir *xlate_dir(struct ctl_table_set *set, struct ctl_dir *dir)
 {
     struct ctl_dir *parent;
     const char *procname;
     if (!dir->header.parent)
         return &set->dir;
     parent = xlate_dir(set, dir->header.parent);
     if (IS_ERR(parent))
         return parent;
     procname = dir->header.ctl_table[0].procname;
     return find_subdir(parent, procname, strlen(procname));
 }
 
 static int sysctl_follow_link(struct ctl_table_header **phead,
     struct ctl_table **pentry)
 {
     struct ctl_table_header *head;
     struct ctl_table_root *root;
     struct ctl_table_set *set;
     struct ctl_table *entry;
     struct ctl_dir *dir;
     int ret;
 
     spin_lock(&sysctl_lock);
     root = (*pentry)->data;
     set = lookup_header_set(root);
     dir = xlate_dir(set, (*phead)->parent);
     if (IS_ERR(dir))
         ret = PTR_ERR(dir);
     else {
         const char *procname = (*pentry)->procname;
         head = NULL;
         entry = find_entry(&head, dir, procname, strlen(procname));
         ret = -ENOENT;
         if (entry && use_table(head)) {
             unuse_table(*phead);
             *phead = head;
             *pentry = entry;
             ret = 0;
         }
     }
 
     spin_unlock(&sysctl_lock);
     return ret;
 }
 
 static int sysctl_err(const char *path, struct ctl_table *table, char *fmt, ...)
 {
     struct va_format vaf;
     va_list args;
 
     va_start(args, fmt);
     vaf.fmt = fmt;
     vaf.va = &args;
 
     pr_err("sysctl table check failed: %s/%s %pV\n",
            path, table->procname, &vaf);
 
     va_end(args);
     return -EINVAL;
 }
 
 static int sysctl_check_table_array(const char *path, struct ctl_table *table)
 {
     int err = 0;
 
     if ((table->proc_handler == proc_douintvec) ||
         (table->proc_handler == proc_douintvec_minmax)) {
         if (table->maxlen != sizeof(unsigned int))
             err |= sysctl_err(path, table, "array not allowed");
     }
 
     if (table->proc_handler == proc_dou8vec_minmax) {
         if (table->maxlen != sizeof(u8))
             err |= sysctl_err(path, table, "array not allowed");
     }
 
     return err;
 }
 
 static int sysctl_check_table(const char *path, struct ctl_table *table)
 {
     struct ctl_table *entry;
     int err = 0;
     list_for_each_table_entry(entry, table) {
         if (entry->child)
             err |= sysctl_err(path, entry, "Not a file");
 
         if ((entry->proc_handler == proc_dostring) ||
             (entry->proc_handler == proc_dointvec) ||
             (entry->proc_handler == proc_douintvec) ||
             (entry->proc_handler == proc_douintvec_minmax) ||
             (entry->proc_handler == proc_dointvec_minmax) ||
             (entry->proc_handler == proc_dou8vec_minmax) ||
             (entry->proc_handler == proc_dointvec_jiffies) ||
             (entry->proc_handler == proc_dointvec_userhz_jiffies) ||
             (entry->proc_handler == proc_dointvec_ms_jiffies) ||
             (entry->proc_handler == proc_doulongvec_minmax) ||
             (entry->proc_handler == proc_doulongvec_ms_jiffies_minmax)) {
             if (!entry->data)
                 err |= sysctl_err(path, entry, "No data");
             if (!entry->maxlen)
                 err |= sysctl_err(path, entry, "No maxlen");
             else
                 err |= sysctl_check_table_array(path, entry);
         }
         if (!entry->proc_handler)
             err |= sysctl_err(path, entry, "No proc_handler");
 
         if ((entry->mode & (S_IRUGO|S_IWUGO)) != entry->mode)
             err |= sysctl_err(path, entry, "bogus .mode 0%o",
                 entry->mode);
     }
     return err;
 }
 
 static struct ctl_table_header *new_links(struct ctl_dir *dir, struct ctl_table *table,
     struct ctl_table_root *link_root)
 {
     struct ctl_table *link_table, *entry, *link;
     struct ctl_table_header *links;
     struct ctl_node *node;
     char *link_name;
     int nr_entries, name_bytes;
 
     name_bytes = 0;
     nr_entries = 0;
     list_for_each_table_entry(entry, table) {
         nr_entries++;
         name_bytes += strlen(entry->procname) + 1;
     }
 
     links = kzalloc(sizeof(struct ctl_table_header) +
             sizeof(struct ctl_node)*nr_entries +
             sizeof(struct ctl_table)*(nr_entries + 1) +
             name_bytes,
             GFP_KERNEL);
 
     if (!links)
         return NULL;
 
     node = (struct ctl_node *)(links + 1);
     link_table = (struct ctl_table *)(node + nr_entries);
     link_name = (char *)&link_table[nr_entries + 1];
     link = link_table;
 
     list_for_each_table_entry(entry, table) {
         int len = strlen(entry->procname) + 1;
         memcpy(link_name, entry->procname, len);
         link->procname = link_name;
         link->mode = S_IFLNK|S_IRWXUGO;
         link->data = link_root;
         link_name += len;
         link++;
     }
     init_header(links, dir->header.root, dir->header.set, node, link_table);
     links->nreg = nr_entries;
 
     return links;
 }
 
 static bool get_links(struct ctl_dir *dir,
     struct ctl_table *table, struct ctl_table_root *link_root)
 {
     struct ctl_table_header *head;
     struct ctl_table *entry, *link;
 
     /* Are there links available for every entry in table? */
     list_for_each_table_entry(entry, table) {
         const char *procname = entry->procname;
         link = find_entry(&head, dir, procname, strlen(procname));
         if (!link)
             return false;
         if (S_ISDIR(link->mode) && S_ISDIR(entry->mode))
             continue;
         if (S_ISLNK(link->mode) && (link->data == link_root))
             continue;
         return false;
     }
 
     /* The checks passed.  Increase the registration count on the links */
     list_for_each_table_entry(entry, table) {
         const char *procname = entry->procname;
         link = find_entry(&head, dir, procname, strlen(procname));
         head->nreg++;
     }
     return true;
 }
 
 static int insert_links(struct ctl_table_header *head)
 {
     struct ctl_table_set *root_set = &sysctl_table_root.default_set;
     struct ctl_dir *core_parent = NULL;
     struct ctl_table_header *links;
     int err;
 
     if (head->set == root_set)
         return 0;
 
     core_parent = xlate_dir(root_set, head->parent);
     if (IS_ERR(core_parent))
         return 0;
 
     if (get_links(core_parent, head->ctl_table, head->root))
         return 0;
 
     core_parent->header.nreg++;
     spin_unlock(&sysctl_lock);
 
     links = new_links(core_parent, head->ctl_table, head->root);
 
     spin_lock(&sysctl_lock);
     err = -ENOMEM;
     if (!links)
         goto out;
 
     err = 0;
     if (get_links(core_parent, head->ctl_table, head->root)) {
         kfree(links);
         goto out;
     }
 
     err = insert_header(core_parent, links);
     if (err)
         kfree(links);
 out:
     drop_sysctl_table(&core_parent->header);
     return err;
 }
 
 /**
  * __register_sysctl_table - register a leaf sysctl table
  * @set: Sysctl tree to register on
  * @path: The path to the directory the sysctl table is in.
  * @table: the top-level table structure
  *
  * Register a sysctl table hierarchy. @table should be a filled in ctl_table
  * array. A completely 0 filled entry terminates the table.
  *
  * The members of the &struct ctl_table structure are used as follows:
  *
  * procname - the name of the sysctl file under /proc/sys. Set to %NULL to not
  *            enter a sysctl file
  *
  * data - a pointer to data for use by proc_handler
  *
  * maxlen - the maximum size in bytes of the data
  *
  * mode - the file permissions for the /proc/sys file
  *
  * child - must be %NULL.
  *
  * proc_handler - the text handler routine (described below)
  *
  * extra1, extra2 - extra pointers usable by the proc handler routines
  *
  * Leaf nodes in the sysctl tree will be represented by a single file
  * under /proc; non-leaf nodes will be represented by directories.
  *
  * There must be a proc_handler routine for any terminal nodes.
  * Several default handlers are available to cover common cases -
  *
  * proc_dostring(), proc_dointvec(), proc_dointvec_jiffies(),
  * proc_dointvec_userhz_jiffies(), proc_dointvec_minmax(),
  * proc_doulongvec_ms_jiffies_minmax(), proc_doulongvec_minmax()
  *
  * It is the handler's job to read the input buffer from user memory
  * and process it. The handler should return 0 on success.
  *
  * This routine returns %NULL on a failure to register, and a pointer
  * to the table header on success.
  */
 struct ctl_table_header *__register_sysctl_table(
     struct ctl_table_set *set,
     const char *path, struct ctl_table *table)
 {
     struct ctl_table_root *root = set->dir.header.root;
     struct ctl_table_header *header;
     const char *name, *nextname;
     struct ctl_dir *dir;
     struct ctl_table *entry;
     struct ctl_node *node;
     int nr_entries = 0;
 
     list_for_each_table_entry(entry, table)
         nr_entries++;
 
     header = kzalloc(sizeof(struct ctl_table_header) +
              sizeof(struct ctl_node)*nr_entries, GFP_KERNEL_ACCOUNT);
     if (!header)
         return NULL;
 
     node = (struct ctl_node *)(header + 1);
     init_header(header, root, set, node, table);
     if (sysctl_check_table(path, table))
         goto fail;
 
     spin_lock(&sysctl_lock);
     dir = &set->dir;
     /* Reference moved down the diretory tree get_subdir */
     dir->header.nreg++;
     spin_unlock(&sysctl_lock);
 
     /* Find the directory for the ctl_table */
     for (name = path; name; name = nextname) {
         int namelen;
         nextname = strchr(name, '/');
         if (nextname) {
             namelen = nextname - name;
             nextname++;
         } else {
             namelen = strlen(name);
         }
         if (namelen == 0)
             continue;
 
         dir = get_subdir(dir, name, namelen);
         if (IS_ERR(dir))
             goto fail;
     }
 
     spin_lock(&sysctl_lock);
     if (insert_header(dir, header))
         goto fail_put_dir_locked;
 
     drop_sysctl_table(&dir->header);
     spin_unlock(&sysctl_lock);
 
     return header;
 
 fail_put_dir_locked:
     drop_sysctl_table(&dir->header);
     spin_unlock(&sysctl_lock);
 fail:
     kfree(header);
     dump_stack();
     return NULL;
 }
 
 /**
  * register_sysctl - register a sysctl table
  * @path: The path to the directory the sysctl table is in.
  * @table: the table structure
  *
  * Register a sysctl table. @table should be a filled in ctl_table
  * array. A completely 0 filled entry terminates the table.
  *
  * See __register_sysctl_table for more details.
  */
 struct ctl_table_header *register_sysctl(const char *path, struct ctl_table *table)
 {
     return __register_sysctl_table(&sysctl_table_root.default_set,
                     path, table);
 }
 EXPORT_SYMBOL(register_sysctl);
 
 /**
  * __register_sysctl_init() - register sysctl table to path
  * @path: path name for sysctl base
  * @table: This is the sysctl table that needs to be registered to the path
  * @table_name: The name of sysctl table, only used for log printing when
  *              registration fails
  *
  * The sysctl interface is used by userspace to query or modify at runtime
  * a predefined value set on a variable. These variables however have default
  * values pre-set. Code which depends on these variables will always work even
  * if register_sysctl() fails. If register_sysctl() fails you'd just loose the
  * ability to query or modify the sysctls dynamically at run time. Chances of
  * register_sysctl() failing on init are extremely low, and so for both reasons
  * this function does not return any error as it is used by initialization code.
  *
  * Context: Can only be called after your respective sysctl base path has been
  * registered. So for instance, most base directories are registered early on
  * init before init levels are processed through proc_sys_init() and
  * sysctl_init_bases().
  */
 void __init __register_sysctl_init(const char *path, struct ctl_table *table,
                  const char *table_name)
 {
     struct ctl_table_header *hdr = register_sysctl(path, table);
 
     if (unlikely(!hdr)) {
         pr_err("failed when register_sysctl %s to %s\n", table_name, path);
         return;
     }
     kmemleak_not_leak(hdr);
 }
 
 static char *append_path(const char *path, char *pos, const char *name)
 {
     int namelen;
     namelen = strlen(name);
     if (((pos - path) + namelen + 2) >= PATH_MAX)
         return NULL;
     memcpy(pos, name, namelen);
     pos[namelen] = '/';
     pos[namelen + 1] = '\0';
     pos += namelen + 1;
     return pos;
 }
 
 static int count_subheaders(struct ctl_table *table)
 {
     int has_files = 0;
     int nr_subheaders = 0;
     struct ctl_table *entry;
 
     /* special case: no directory and empty directory */
     if (!table || !table->procname)
         return 1;
 
     list_for_each_table_entry(entry, table) {
         if (entry->child)
             nr_subheaders += count_subheaders(entry->child);
         else
             has_files = 1;
     }
     return nr_subheaders + has_files;
 }
 
 static int register_leaf_sysctl_tables(const char *path, char *pos,
     struct ctl_table_header ***subheader, struct ctl_table_set *set,
     struct ctl_table *table)
 {
     struct ctl_table *ctl_table_arg = NULL;
     struct ctl_table *entry, *files;
     int nr_files = 0;
     int nr_dirs = 0;
     int err = -ENOMEM;
 
     list_for_each_table_entry(entry, table) {
         if (entry->child)
             nr_dirs++;
         else
             nr_files++;
     }
 
     files = table;
     /* If there are mixed files and directories we need a new table */
     if (nr_dirs && nr_files) {
         struct ctl_table *new;
         files = kcalloc(nr_files + 1, sizeof(struct ctl_table),
                 GFP_KERNEL);
         if (!files)
             goto out;
 
         ctl_table_arg = files;
         new = files;
 
         list_for_each_table_entry(entry, table) {
             if (entry->child)
                 continue;
             *new = *entry;
             new++;
         }
     }
 
     /* Register everything except a directory full of subdirectories */
     if (nr_files || !nr_dirs) {
         struct ctl_table_header *header;
         header = __register_sysctl_table(set, path, files);
         if (!header) {
             kfree(ctl_table_arg);
             goto out;
         }
 
         /* Remember if we need to free the file table */
         header->ctl_table_arg = ctl_table_arg;
         **subheader = header;
         (*subheader)++;
     }
 
     /* Recurse into the subdirectories. */
     list_for_each_table_entry(entry, table) {
         char *child_pos;
 
         if (!entry->child)
             continue;
 
         err = -ENAMETOOLONG;
         child_pos = append_path(path, pos, entry->procname);
         if (!child_pos)
             goto out;
 
         err = register_leaf_sysctl_tables(path, child_pos, subheader,
                           set, entry->child);
         pos[0] = '\0';
         if (err)
             goto out;
     }
     err = 0;
 out:
     /* On failure our caller will unregister all registered subheaders */
     return err;
 }
 
 /**
  * __register_sysctl_paths - register a sysctl table hierarchy
  * @set: Sysctl tree to register on
  * @path: The path to the directory the sysctl table is in.
  * @table: the top-level table structure
  *
  * Register a sysctl table hierarchy. @table should be a filled in ctl_table
  * array. A completely 0 filled entry terminates the table.
  *
  * See __register_sysctl_table for more details.
  */
 struct ctl_table_header *__register_sysctl_paths(
     struct ctl_table_set *set,
     const struct ctl_path *path, struct ctl_table *table)
 {
     struct ctl_table *ctl_table_arg = table;
     int nr_subheaders = count_subheaders(table);
     struct ctl_table_header *header = NULL, **subheaders, **subheader;
     const struct ctl_path *component;
     char *new_path, *pos;
 
     pos = new_path = kmalloc(PATH_MAX, GFP_KERNEL);
     if (!new_path)
         return NULL;
 
     pos[0] = '\0';
     for (component = path; component->procname; component++) {
         pos = append_path(new_path, pos, component->procname);
         if (!pos)
             goto out;
     }
     while (table->procname && table->child && !table[1].procname) {
         pos = append_path(new_path, pos, table->procname);
         if (!pos)
             goto out;
         table = table->child;
     }
     if (nr_subheaders == 1) {
         header = __register_sysctl_table(set, new_path, table);
         if (header)
             header->ctl_table_arg = ctl_table_arg;
     } else {
         header = kzalloc(sizeof(*header) +
                  sizeof(*subheaders)*nr_subheaders, GFP_KERNEL);
         if (!header)
             goto out;
 
         subheaders = (struct ctl_table_header **) (header + 1);
         subheader = subheaders;
         header->ctl_table_arg = ctl_table_arg;
 
         if (register_leaf_sysctl_tables(new_path, pos, &subheader,
                         set, table))
             goto err_register_leaves;
     }
 
 out:
     kfree(new_path);
     return header;
 
 err_register_leaves:
     while (subheader > subheaders) {
         struct ctl_table_header *subh = *(--subheader);
         struct ctl_table *table = subh->ctl_table_arg;
         unregister_sysctl_table(subh);
         kfree(table);
     }
     kfree(header);
     header = NULL;
     goto out;
 }
 
 /**
  * register_sysctl_paths - register a sysctl table hierarchy
  * @path: The path to the directory the sysctl table is in.
  * @table: the top-level table structure
  *
  * Register a sysctl table hierarchy. @table should be a filled in ctl_table
  * array. A completely 0 filled entry terminates the table.
  *
  * See __register_sysctl_paths for more details.
  */
 struct ctl_table_header *register_sysctl_paths(const struct ctl_path *path,
                         struct ctl_table *table)
 {
     return __register_sysctl_paths(&sysctl_table_root.default_set,
                     path, table);
 }
 EXPORT_SYMBOL(register_sysctl_paths);
 
 /**
  * register_sysctl_table - register a sysctl table hierarchy
  * @table: the top-level table structure
  *
  * Register a sysctl table hierarchy. @table should be a filled in ctl_table
  * array. A completely 0 filled entry terminates the table.
  *
  * See register_sysctl_paths for more details.
  */
 struct ctl_table_header *register_sysctl_table(struct ctl_table *table)
 {
     static const struct ctl_path null_path[] = { {} };
 
     return register_sysctl_paths(null_path, table);
 }
 EXPORT_SYMBOL(register_sysctl_table);
 
 int __register_sysctl_base(struct ctl_table *base_table)
 {
     struct ctl_table_header *hdr;
 
     hdr = register_sysctl_table(base_table);
     kmemleak_not_leak(hdr);
     return 0;
 }
 
 static void put_links(struct ctl_table_header *header)
 {
     struct ctl_table_set *root_set = &sysctl_table_root.default_set;
     struct ctl_table_root *root = header->root;
     struct ctl_dir *parent = header->parent;
     struct ctl_dir *core_parent;
     struct ctl_table *entry;
 
     if (header->set == root_set)
         return;
 
     core_parent = xlate_dir(root_set, parent);
     if (IS_ERR(core_parent))
         return;
 
     list_for_each_table_entry(entry, header->ctl_table) {
         struct ctl_table_header *link_head;
         struct ctl_table *link;
         const char *name = entry->procname;
 
         link = find_entry(&link_head, core_parent, name, strlen(name));
         if (link &&
             ((S_ISDIR(link->mode) && S_ISDIR(entry->mode)) ||
              (S_ISLNK(link->mode) && (link->data == root)))) {
             drop_sysctl_table(link_head);
         }
         else {
             pr_err("sysctl link missing during unregister: ");
             sysctl_print_dir(parent);
             pr_cont("%s\n", name);
         }
     }
 }
 
 static void drop_sysctl_table(struct ctl_table_header *header)
 {
     struct ctl_dir *parent = header->parent;
 
     if (--header->nreg)
         return;
 
     if (parent) {
         put_links(header);
         start_unregistering(header);
     }
 
     if (!--header->count)
         kfree_rcu(header, rcu);
 
     if (parent)
         drop_sysctl_table(&parent->header);
 }
 
 /**
  * unregister_sysctl_table - unregister a sysctl table hierarchy
  * @header: the header returned from register_sysctl_table
  *
  * Unregisters the sysctl table and all children. proc entries may not
  * actually be removed until they are no longer used by anyone.
  */
 void unregister_sysctl_table(struct ctl_table_header * header)
 {
     int nr_subheaders;
     might_sleep();
 
     if (header == NULL)
         return;
 
     nr_subheaders = count_subheaders(header->ctl_table_arg);
     if (unlikely(nr_subheaders > 1)) {
         struct ctl_table_header **subheaders;
         int i;
 
         subheaders = (struct ctl_table_header **)(header + 1);
         for (i = nr_subheaders -1; i >= 0; i--) {
             struct ctl_table_header *subh = subheaders[i];
             struct ctl_table *table = subh->ctl_table_arg;
             unregister_sysctl_table(subh);
             kfree(table);
         }
         kfree(header);
         return;
     }
 
     spin_lock(&sysctl_lock);
     drop_sysctl_table(header);
     spin_unlock(&sysctl_lock);
 }
 EXPORT_SYMBOL(unregister_sysctl_table);
 
 void setup_sysctl_set(struct ctl_table_set *set,
     struct ctl_table_root *root,
     int (*is_seen)(struct ctl_table_set *))
 {
     memset(set, 0, sizeof(*set));
     set->is_seen = is_seen;
     init_header(&set->dir.header, root, set, NULL, root_table);
 }
 
 void retire_sysctl_set(struct ctl_table_set *set)
 {
     WARN_ON(!RB_EMPTY_ROOT(&set->dir.root));
 }
 
 int __init proc_sys_init(void)
 {
     struct proc_dir_entry *proc_sys_root;
 
     proc_sys_root = proc_mkdir("sys", NULL);
     proc_sys_root->proc_iops = &proc_sys_dir_operations;
     proc_sys_root->proc_dir_ops = &proc_sys_dir_file_operations;
     proc_sys_root->nlink = 0;
 
     return sysctl_init_bases();
 }
 
 struct sysctl_alias {
     const char *kernel_param;
     const char *sysctl_param;
 };
 
 /*
  * Historically some settings had both sysctl and a command line parameter.
  * With the generic sysctl. parameter support, we can handle them at a single
  * place and only keep the historical name for compatibility. This is not meant
  * to add brand new aliases. When adding existing aliases, consider whether
  * the possibly different moment of changing the value (e.g. from early_param
  * to the moment do_sysctl_args() is called) is an issue for the specific
  * parameter.
  */
 static const struct sysctl_alias sysctl_aliases[] = {
     {"hardlockup_all_cpu_backtrace",    "kernel.hardlockup_all_cpu_backtrace" },
     {"hung_task_panic",         "kernel.hung_task_panic" },
     {"numa_zonelist_order",         "vm.numa_zonelist_order" },
     {"softlockup_all_cpu_backtrace",    "kernel.softlockup_all_cpu_backtrace" },
     {"softlockup_panic",            "kernel.softlockup_panic" },
     { }
 };
 
 static const char *sysctl_find_alias(char *param)
 {
     const struct sysctl_alias *alias;
 
     for (alias = &sysctl_aliases[0]; alias->kernel_param != NULL; alias++) {
         if (strcmp(alias->kernel_param, param) == 0)
             return alias->sysctl_param;
     }
 
     return NULL;
 }
 
 /* Set sysctl value passed on kernel command line. */
 static int process_sysctl_arg(char *param, char *val,
                    const char *unused, void *arg)
 {
     char *path;
     struct vfsmount **proc_mnt = arg;
     struct file_system_type *proc_fs_type;
     struct file *file;
     int len;
     int err;
     loff_t pos = 0;
     ssize_t wret;
 
     if (strncmp(param, "sysctl", sizeof("sysctl") - 1) == 0) {
         param += sizeof("sysctl") - 1;
 
         if (param[0] != '/' && param[0] != '.')
             return 0;
 
         param++;
     } else {
         param = (char *) sysctl_find_alias(param);
         if (!param)
             return 0;
     }
 
     if (!val)
         return -EINVAL;
     len = strlen(val);
     if (len == 0)
         return -EINVAL;
 
     /*
      * To set sysctl options, we use a temporary mount of proc, look up the
      * respective sys/ file and write to it. To avoid mounting it when no
      * options were given, we mount it only when the first sysctl option is
      * found. Why not a persistent mount? There are problems with a
      * persistent mount of proc in that it forces userspace not to use any
      * proc mount options.
      */
     if (!*proc_mnt) {
         proc_fs_type = get_fs_type("proc");
         if (!proc_fs_type) {
             pr_err("Failed to find procfs to set sysctl from command line\n");
             return 0;
         }
         *proc_mnt = kern_mount(proc_fs_type);
         put_filesystem(proc_fs_type);
         if (IS_ERR(*proc_mnt)) {
             pr_err("Failed to mount procfs to set sysctl from command line\n");
             return 0;
         }
     }
 
     path = kasprintf(GFP_KERNEL, "sys/%s", param);
     if (!path)
         panic("%s: Failed to allocate path for %s\n", __func__, param);
     strreplace(path, '.', '/');
 
     file = file_open_root_mnt(*proc_mnt, path, O_WRONLY, 0);
     if (IS_ERR(file)) {
         err = PTR_ERR(file);
         if (err == -ENOENT)
             pr_err("Failed to set sysctl parameter '%s=%s': parameter not found\n",
                 param, val);
         else if (err == -EACCES)
             pr_err("Failed to set sysctl parameter '%s=%s': permission denied (read-only?)\n",
                 param, val);
         else
             pr_err("Error %pe opening proc file to set sysctl parameter '%s=%s'\n",
                 file, param, val);
         goto out;
     }
     wret = kernel_write(file, val, len, &pos);
     if (wret < 0) {
         err = wret;
         if (err == -EINVAL)
             pr_err("Failed to set sysctl parameter '%s=%s': invalid value\n",
                 param, val);
         else
             pr_err("Error %pe writing to proc file to set sysctl parameter '%s=%s'\n",
                 ERR_PTR(err), param, val);
     } else if (wret != len) {
         pr_err("Wrote only %zd bytes of %d writing to proc file %s to set sysctl parameter '%s=%s\n",
             wret, len, path, param, val);
     }
 
     err = filp_close(file, NULL);
     if (err)
         pr_err("Error %pe closing proc file to set sysctl parameter '%s=%s\n",
             ERR_PTR(err), param, val);
 out:
     kfree(path);
     return 0;
 }
 
 void do_sysctl_args(void)
 {
     char *command_line;
     struct vfsmount *proc_mnt = NULL;
 
     command_line = kstrdup(saved_command_line, GFP_KERNEL);
     if (!command_line)
         panic("%s: Failed to allocate copy of command line\n", __func__);
 
     parse_args("Setting sysctl args", command_line,
            NULL, 0, -1, -1, &proc_mnt, process_sysctl_arg);
 
     if (proc_mnt)
         kern_unmount(proc_mnt);
 
     kfree(command_line);
 }

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