fs/sysfs/mount.c

0001 // SPDX-License-Identifier: GPL-2.0
0002 /*
0003  * fs/sysfs/symlink.c - operations for initializing and mounting sysfs
0004  *
0005  * Copyright (c) 2001-3 Patrick Mochel
0006  * Copyright (c) 2007 SUSE Linux Products GmbH
0007  * Copyright (c) 2007 Tejun Heo <teheo@suse.de>
0008  *
0009  * Please see Documentation/filesystems/sysfs.rst for more information.
0010  */
0011
0012 #include <linux/fs.h>
0013 #include <linux/magic.h>
0014 #include <linux/mount.h>
0015 #include <linux/init.h>
0016 #include <linux/slab.h>
0017 #include <linux/user_namespace.h>
0018 #include <linux/fs_context.h>
0019 #include <net/net_namespace.h>
0020
0021 #include "sysfs.h"
0022
0023 static struct kernfs_root *sysfs_root;
0024 struct kernfs_node *sysfs_root_kn;
0025
0026 static int sysfs_get_tree(struct fs_context *fc)
0027 {
0028     struct kernfs_fs_context *kfc = fc->fs_private;
0029     int ret;
0030
0031     ret = kernfs_get_tree(fc);
0032     if (ret)
0033         return ret;
0034
0035     if (kfc->new_sb_created)
0036         fc->root->d_sb->s_iflags |= SB_I_USERNS_VISIBLE;
0037     return 0;
0038 }
0039
0040 static void sysfs_fs_context_free(struct fs_context *fc)
0041 {
0042     struct kernfs_fs_context *kfc = fc->fs_private;
0043
0044     if (kfc->ns_tag)
0045         kobj_ns_drop(KOBJ_NS_TYPE_NET, kfc->ns_tag);
0046     kernfs_free_fs_context(fc);
0047     kfree(kfc);
0048 }
0049
0050 static const struct fs_context_operations sysfs_fs_context_ops = {
0051     .free       = sysfs_fs_context_free,
0052     .get_tree   = sysfs_get_tree,
0053 };
0054
0055 static int sysfs_init_fs_context(struct fs_context *fc)
0056 {
0057     struct kernfs_fs_context *kfc;
0058     struct net *netns;
0059
0060     if (!(fc->sb_flags & SB_KERNMOUNT)) {
0061         if (!kobj_ns_current_may_mount(KOBJ_NS_TYPE_NET))
0062             return -EPERM;
0063     }
0064
0065     kfc = kzalloc(sizeof(struct kernfs_fs_context), GFP_KERNEL);
0066     if (!kfc)
0067         return -ENOMEM;
0068
0069     kfc->ns_tag = netns = kobj_ns_grab_current(KOBJ_NS_TYPE_NET);
0070     kfc->root = sysfs_root;
0071     kfc->magic = SYSFS_MAGIC;
0072     fc->fs_private = kfc;
0073     fc->ops = &sysfs_fs_context_ops;
0074     if (netns) {
0075         put_user_ns(fc->user_ns);
0076         fc->user_ns = get_user_ns(netns->user_ns);
0077     }
0078     fc->global = true;
0079     return 0;
0080 }
0081
0082 static void sysfs_kill_sb(struct super_block *sb)
0083 {
0084     void *ns = (void *)kernfs_super_ns(sb);
0085
0086     kernfs_kill_sb(sb);
0087     kobj_ns_drop(KOBJ_NS_TYPE_NET, ns);
0088 }
0089
0090 static struct file_system_type sysfs_fs_type = {
0091     .name           = "sysfs",
0092     .init_fs_context    = sysfs_init_fs_context,
0093     .kill_sb        = sysfs_kill_sb,
0094     .fs_flags       = FS_USERNS_MOUNT,
0095 };
0096
0097 int __init sysfs_init(void)
0098 {
0099     int err;
0100
0101     sysfs_root = kernfs_create_root(NULL, KERNFS_ROOT_EXTRA_OPEN_PERM_CHECK,
0102                     NULL);
0103     if (IS_ERR(sysfs_root))
0104         return PTR_ERR(sysfs_root);
0105
0106     sysfs_root_kn = kernfs_root_to_node(sysfs_root);
0107
0108     err = register_filesystem(&sysfs_fs_type);
0109     if (err) {
0110         kernfs_destroy_root(sysfs_root);
0111         return err;
0112     }
0113
0114     return 0;
0115 }