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/magic.h>
  17 #include <linux/mount.h>
  18 #include <linux/init.h>
  19 #include <linux/user_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 struct dentry *sysfs_mount(struct file_system_type *fs_type,
  27         int flags, const char *dev_name, void *data)
  28 {
  29         struct dentry *root;
  30         void *ns;
  31         bool new_sb;
  32
  33         if (!(flags & MS_KERNMOUNT)) {
  34                 if (!capable(CAP_SYS_ADMIN) && !fs_fully_visible(fs_type))
  35                         return ERR_PTR(-EPERM);
  36
  37                 if (!kobj_ns_current_may_mount(KOBJ_NS_TYPE_NET))
  38                         return ERR_PTR(-EPERM);
  39         }
  40
  41         ns = kobj_ns_grab_current(KOBJ_NS_TYPE_NET);
  42         root = kernfs_mount_ns(fs_type, flags, sysfs_root,
  43                                 SYSFS_MAGIC, &new_sb, ns);
  44         if (IS_ERR(root) || !new_sb)
  45                 kobj_ns_drop(KOBJ_NS_TYPE_NET, ns);
  46         return root;
  47 }
  48
  49 static void sysfs_kill_sb(struct super_block *sb)
  50 {
  51         void *ns = (void *)kernfs_super_ns(sb);
  52
  53         kernfs_kill_sb(sb);
  54         kobj_ns_drop(KOBJ_NS_TYPE_NET, ns);
  55 }
  56
  57 static struct file_system_type sysfs_fs_type = {
  58         .name           = "sysfs",
  59         .mount          = sysfs_mount,
  60         .kill_sb        = sysfs_kill_sb,
  61         .fs_flags       = FS_USERNS_MOUNT,
  62 };
  63
  64 int __init sysfs_init(void)
  65 {
  66         int err;
  67
  68         sysfs_root = kernfs_create_root(NULL, KERNFS_ROOT_EXTRA_OPEN_PERM_CHECK,
  69                                         NULL);
  70         if (IS_ERR(sysfs_root))
  71                 return PTR_ERR(sysfs_root);
  72
  73         sysfs_root_kn = sysfs_root->kn;
  74
  75         err = register_filesystem(&sysfs_fs_type);
  76         if (err) {
  77                 kernfs_destroy_root(sysfs_root);
  78                 return err;
  79         }
  80
  81         return 0;
  82 }