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 (!kobj_ns_current_may_mount(KOBJ_NS_TYPE_NET))
  35                         return ERR_PTR(-EPERM);
  36         }
  37
  38         ns = kobj_ns_grab_current(KOBJ_NS_TYPE_NET);
  39         root = kernfs_mount_ns(fs_type, flags, sysfs_root,
  40                                 SYSFS_MAGIC, &new_sb, ns);
  41         if (IS_ERR(root) || !new_sb)
  42                 kobj_ns_drop(KOBJ_NS_TYPE_NET, ns);
  43         else if (new_sb)
  44                 /* Userspace would break if executables appear on sysfs */
  45                 root->d_sb->s_iflags |= SB_I_NOEXEC;
  46
  47         return root;
  48 }
  49
  50 static void sysfs_kill_sb(struct super_block *sb)
  51 {
  52         void *ns = (void *)kernfs_super_ns(sb);
  53
  54         kernfs_kill_sb(sb);
  55         kobj_ns_drop(KOBJ_NS_TYPE_NET, ns);
  56 }
  57
  58 static struct file_system_type sysfs_fs_type = {
  59         .name           = "sysfs",
  60         .mount          = sysfs_mount,
  61         .kill_sb        = sysfs_kill_sb,
  62         .fs_flags       = FS_USERNS_VISIBLE | FS_USERNS_MOUNT,
  63 };
  64
  65 int __init sysfs_init(void)
  66 {
  67         int err;
  68
  69         sysfs_root = kernfs_create_root(NULL, KERNFS_ROOT_EXTRA_OPEN_PERM_CHECK,
  70                                         NULL);
  71         if (IS_ERR(sysfs_root))
  72                 return PTR_ERR(sysfs_root);
  73
  74         sysfs_root_kn = sysfs_root->kn;
  75
  76         err = register_filesystem(&sysfs_fs_type);
  77         if (err) {
  78                 kernfs_destroy_root(sysfs_root);
  79                 return err;
  80         }
  81
  82         return 0;
  83 }