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configfs: fix a race in configfs_{,un}register_subsystem()

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When configfs_register_subsystem() or configfs_unregister_subsystem()
is executing link_group() or unlink_group(),
it is possible that two processes add or delete list concurrently.
Some unfortunate interleavings of them can cause kernel panic.

One of cases is:
A --> B --> C --> D
A <-- B <-- C <-- D

     delete list_head *B        |      delete list_head *C
--------------------------------|-----------------------------------
configfs_unregister_subsystem   |   configfs_unregister_subsystem
  unlink_group                  |     unlink_group
    unlink_obj                  |       unlink_obj
      list_del_init             |         list_del_init
        __list_del_entry        |           __list_del_entry
          __list_del            |             __list_del
            // next == C        |
            next->prev = prev   |
                                |               next->prev = prev
            prev->next = next   |
                                |                 // prev == B
                                |                 prev->next = next

Fix this by adding mutex when calling link_group() or unlink_group(),
but parent configfs_subsystem is NULL when config_item is root.
So I create a mutex configfs_subsystem_mutex.

Fixes: 7063fbf226 ("[PATCH] configfs: User-driven configuration filesystem")
Signed-off-by: ChenXiaoSong <chenxiaosong2@huawei.com>
Signed-off-by: Laibin Qiu <qiulaibin@huawei.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
This commit is contained in:
ChenXiaoSong 2022-02-15 15:10:30 +08:00 committed by Christoph Hellwig
parent 038101e6b2
commit 84ec758fb2
1 changed files with 14 additions and 0 deletions
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14
fs/configfs/dir.c
View File

@ -34,6 +34,14 @@
*/
DEFINE_SPINLOCK(configfs_dirent_lock);
/*
* All of link_obj/unlink_obj/link_group/unlink_group require that
* subsys->su_mutex is held.
* But parent configfs_subsystem is NULL when config_item is root.
* Use this mutex when config_item is root.
*/
static DEFINE_MUTEX(configfs_subsystem_mutex);
static void configfs_d_iput(struct dentry * dentry,
struct inode * inode)
{
@ -1859,7 +1867,9 @@ int configfs_register_subsystem(struct configfs_subsystem *subsys)
group->cg_item.ci_name = group->cg_item.ci_namebuf;
sd = root->d_fsdata;
mutex_lock(&configfs_subsystem_mutex);
link_group(to_config_group(sd->s_element), group);
mutex_unlock(&configfs_subsystem_mutex);
inode_lock_nested(d_inode(root), I_MUTEX_PARENT);
@ -1884,7 +1894,9 @@ int configfs_register_subsystem(struct configfs_subsystem *subsys)
inode_unlock(d_inode(root));
if (err) {
mutex_lock(&configfs_subsystem_mutex);
unlink_group(group);
mutex_unlock(&configfs_subsystem_mutex);
configfs_release_fs();
}
put_fragment(frag);
@ -1931,7 +1943,9 @@ void configfs_unregister_subsystem(struct configfs_subsystem *subsys)
dput(dentry);
mutex_lock(&configfs_subsystem_mutex);
unlink_group(group);
mutex_unlock(&configfs_subsystem_mutex);
configfs_release_fs();
}