LXR linux/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
  23static struct kernfs_root *sysfs_root;
  24struct kernfs_node *sysfs_root_kn;
  25
  26static 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
  40static 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
  50static const struct fs_context_operations sysfs_fs_context_ops = {
  51        .free           = sysfs_fs_context_free,
  52        .get_tree       = sysfs_get_tree,
  53};
  54
  55static 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
  82static 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
  90static 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
  97int __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}
 116