fs/sysfs/mount.c

   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
  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
  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
  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
  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
  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 = sysfs_root->kn;
 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 }