xref: /linux/fs/sysfs/mount.c (revision 4f2c0a4acffbec01079c28f839422e64ddeff004)
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * fs/sysfs/symlink.c - operations for initializing and mounting sysfs
4  *
5  * Copyright (c) 2001-3 Patrick Mochel
6  * Copyright (c) 2007 SUSE Linux Products GmbH
7  * Copyright (c) 2007 Tejun Heo <teheo@suse.de>
8  *
9  * Please see Documentation/filesystems/sysfs.rst for more information.
10  */
11 
12 #include <linux/fs.h>
13 #include <linux/magic.h>
14 #include <linux/mount.h>
15 #include <linux/init.h>
16 #include <linux/slab.h>
17 #include <linux/user_namespace.h>
18 #include <linux/fs_context.h>
19 #include <net/net_namespace.h>
20 
21 #include "sysfs.h"
22 
23 static struct kernfs_root *sysfs_root;
24 struct kernfs_node *sysfs_root_kn;
25 
sysfs_get_tree(struct fs_context * fc)26 static int sysfs_get_tree(struct fs_context *fc)
27 {
28 	struct kernfs_fs_context *kfc = fc->fs_private;
29 	int ret;
30 
31 	ret = kernfs_get_tree(fc);
32 	if (ret)
33 		return ret;
34 
35 	if (kfc->new_sb_created)
36 		fc->root->d_sb->s_iflags |= SB_I_USERNS_VISIBLE;
37 	return 0;
38 }
39 
sysfs_fs_context_free(struct fs_context * fc)40 static void sysfs_fs_context_free(struct fs_context *fc)
41 {
42 	struct kernfs_fs_context *kfc = fc->fs_private;
43 
44 	if (kfc->ns_tag)
45 		kobj_ns_drop(KOBJ_NS_TYPE_NET, kfc->ns_tag);
46 	kernfs_free_fs_context(fc);
47 	kfree(kfc);
48 }
49 
50 static const struct fs_context_operations sysfs_fs_context_ops = {
51 	.free		= sysfs_fs_context_free,
52 	.get_tree	= sysfs_get_tree,
53 };
54 
sysfs_init_fs_context(struct fs_context * fc)55 static int sysfs_init_fs_context(struct fs_context *fc)
56 {
57 	struct kernfs_fs_context *kfc;
58 	struct net *netns;
59 
60 	if (!(fc->sb_flags & SB_KERNMOUNT)) {
61 		if (!kobj_ns_current_may_mount(KOBJ_NS_TYPE_NET))
62 			return -EPERM;
63 	}
64 
65 	kfc = kzalloc(sizeof(struct kernfs_fs_context), GFP_KERNEL);
66 	if (!kfc)
67 		return -ENOMEM;
68 
69 	kfc->ns_tag = netns = kobj_ns_grab_current(KOBJ_NS_TYPE_NET);
70 	kfc->root = sysfs_root;
71 	kfc->magic = SYSFS_MAGIC;
72 	fc->fs_private = kfc;
73 	fc->ops = &sysfs_fs_context_ops;
74 	if (netns) {
75 		put_user_ns(fc->user_ns);
76 		fc->user_ns = get_user_ns(netns->user_ns);
77 	}
78 	fc->global = true;
79 	return 0;
80 }
81 
sysfs_kill_sb(struct super_block * sb)82 static void sysfs_kill_sb(struct super_block *sb)
83 {
84 	void *ns = (void *)kernfs_super_ns(sb);
85 
86 	kernfs_kill_sb(sb);
87 	kobj_ns_drop(KOBJ_NS_TYPE_NET, ns);
88 }
89 
90 static struct file_system_type sysfs_fs_type = {
91 	.name			= "sysfs",
92 	.init_fs_context	= sysfs_init_fs_context,
93 	.kill_sb		= sysfs_kill_sb,
94 	.fs_flags		= FS_USERNS_MOUNT,
95 };
96 
sysfs_init(void)97 int __init sysfs_init(void)
98 {
99 	int err;
100 
101 	sysfs_root = kernfs_create_root(NULL, KERNFS_ROOT_EXTRA_OPEN_PERM_CHECK,
102 					NULL);
103 	if (IS_ERR(sysfs_root))
104 		return PTR_ERR(sysfs_root);
105 
106 	sysfs_root_kn = kernfs_root_to_node(sysfs_root);
107 
108 	err = register_filesystem(&sysfs_fs_type);
109 	if (err) {
110 		kernfs_destroy_root(sysfs_root);
111 		return err;
112 	}
113 
114 	return 0;
115 }
116