fs/sysfs/mount.c

   1 /*
   2  * fs/sysfs/symlink.c - operations for initializing and mounting sysfs
   3  *
   4  * Copyright (c) 2001-3 Patrick Mochel
   5  * Copyright (c) 2007 SUSE Linux Products GmbH
   6  * Copyright (c) 2007 Tejun Heo <teheo@suse.de>
   7  *
   8  * This file is released under the GPLv2.
   9  *
  10  * Please see Documentation/filesystems/sysfs.txt for more information.
  11  */
  12
  13 #define DEBUG
  14
  15 #include <linux/fs.h>
  16 #include <linux/mount.h>
  17 #include <linux/init.h>
  18 #include <linux/user_namespace.h>
  19
  20 #include "sysfs.h"
  21
  22 static struct kernfs_root *sysfs_root;
  23 struct kernfs_node *sysfs_root_kn;
  24
  25 static struct dentry *sysfs_mount(struct file_system_type *fs_type,
  26         int flags, const char *dev_name, void *data)
  27 {
  28         struct dentry *root;
  29         void *ns;
  30         bool new_sb;
  31
  32         if (!(flags & MS_KERNMOUNT)) {
  33                 if (!capable(CAP_SYS_ADMIN) && !fs_fully_visible(fs_type))
  34                         return ERR_PTR(-EPERM);
  35
  36                 if (!kobj_ns_current_may_mount(KOBJ_NS_TYPE_NET))
  37                         return ERR_PTR(-EPERM);
  38         }
  39
  40         ns = kobj_ns_grab_current(KOBJ_NS_TYPE_NET);
  41         root = kernfs_mount_ns(fs_type, flags, sysfs_root, &new_sb, ns);
  42         if (IS_ERR(root) || !new_sb)
  43                 kobj_ns_drop(KOBJ_NS_TYPE_NET, ns);
  44         return root;
  45 }
  46
  47 static void sysfs_kill_sb(struct super_block *sb)
  48 {
  49         void *ns = (void *)kernfs_super_ns(sb);
  50
  51         kernfs_kill_sb(sb);
  52         kobj_ns_drop(KOBJ_NS_TYPE_NET, ns);
  53 }
  54
  55 static struct file_system_type sysfs_fs_type = {
  56         .name           = "sysfs",
  57         .mount          = sysfs_mount,
  58         .kill_sb        = sysfs_kill_sb,
  59         .fs_flags       = FS_USERNS_MOUNT,
  60 };
  61
  62 int __init sysfs_init(void)
  63 {
  64         int err;
  65
  66         sysfs_root = kernfs_create_root(NULL, KERNFS_ROOT_EXTRA_OPEN_PERM_CHECK,
  67                                         NULL);
  68         if (IS_ERR(sysfs_root))
  69                 return PTR_ERR(sysfs_root);
  70
  71         sysfs_root_kn = sysfs_root->kn;
  72
  73         err = register_filesystem(&sysfs_fs_type);
  74         if (err) {
  75                 kernfs_destroy_root(sysfs_root);
  76                 return err;
  77         }
  78
  79         return 0;
  80 }