diff options
author | ChenXiaoSong <chenxiaosong2@huawei.com> | 2022-02-15 10:10:30 +0300 |
---|---|---|
committer | Christoph Hellwig <hch@lst.de> | 2022-02-22 20:30:28 +0300 |
commit | 84ec758fb2daa236026506868c8796b0500c047d (patch) | |
tree | ce8ffacc756674199e92e4c9b07a200e715fb801 | |
parent | 038101e6b2cd5c55f888f85db42ea2ad3aecb4b6 (diff) | |
download | linux-84ec758fb2daa236026506868c8796b0500c047d.tar.xz |
configfs: fix a race in configfs_{,un}register_subsystem()
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: 7063fbf22611 ("[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>
-rw-r--r-- | fs/configfs/dir.c | 14 |
1 files changed, 14 insertions, 0 deletions
diff --git a/fs/configfs/dir.c b/fs/configfs/dir.c index d3cd2a94d1e8..d1f9d2632202 100644 --- a/fs/configfs/dir.c +++ b/fs/configfs/dir.c @@ -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(); } |