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.txt 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/user_namespace.h>
  17
  18 #include "sysfs.h"
  19
  20 static struct kernfs_root *sysfs_root;
  21 struct kernfs_node *sysfs_root_kn;
  22
  23 static struct dentry *sysfs_mount(struct file_system_type *fs_type,
  24         int flags, const char *dev_name, void *data)
  25 {
  26         struct dentry *root;
  27         void *ns;
  28         bool new_sb;
  29
  30         if (!(flags & SB_KERNMOUNT)) {
  31                 if (!kobj_ns_current_may_mount(KOBJ_NS_TYPE_NET))
  32                         return ERR_PTR(-EPERM);
  33         }
  34
  35         ns = kobj_ns_grab_current(KOBJ_NS_TYPE_NET);
  36         root = kernfs_mount_ns(fs_type, flags, sysfs_root,
  37                                 SYSFS_MAGIC, &new_sb, ns);
  38         if (IS_ERR(root) || !new_sb)
  39                 kobj_ns_drop(KOBJ_NS_TYPE_NET, ns);
  40         else if (new_sb)
  41                 root->d_sb->s_iflags |= SB_I_USERNS_VISIBLE;
  42
  43         return root;
  44 }
  45
  46 static void sysfs_kill_sb(struct super_block *sb)
  47 {
  48         void *ns = (void *)kernfs_super_ns(sb);
  49
  50         kernfs_kill_sb(sb);
  51         kobj_ns_drop(KOBJ_NS_TYPE_NET, ns);
  52 }
  53
  54 static struct file_system_type sysfs_fs_type = {
  55         .name           = "sysfs",
  56         .mount          = sysfs_mount,
  57         .kill_sb        = sysfs_kill_sb,
  58         .fs_flags       = FS_USERNS_MOUNT,
  59 };
  60
  61 int __init sysfs_init(void)
  62 {
  63         int err;
  64
  65         sysfs_root = kernfs_create_root(NULL, KERNFS_ROOT_EXTRA_OPEN_PERM_CHECK,
  66                                         NULL);
  67         if (IS_ERR(sysfs_root))
  68                 return PTR_ERR(sysfs_root);
  69
  70         sysfs_root_kn = sysfs_root->kn;
  71
  72         err = register_filesystem(&sysfs_fs_type);
  73         if (err) {
  74                 kernfs_destroy_root(sysfs_root);
  75                 return err;
  76         }
  77
  78         return 0;
  79 }