If fscache_alloc_cookie encounters memory allocation failure, it will
go to nomem label and invoke fscache_free_cookie. However,
fscache_alloc_cookie assumes current cookie is already linked into
fscache_cookies and directly calls list_del. This assumption does not
hold since list_add is not called in the above scenario. As a result, it
will lead to Null Pointer Dereference. The stack trace is in the
following.
Call Trace:
__list_del_entry include/linux/list.h:132 [inline]
list_del include/linux/list.h:146 [inline]
fscache_free_cookie fs/fscache/cookie.c:71 [inline]
fscache_free_cookie+0x3f/0x100 fs/fscache/cookie.c:66
fscache_alloc_cookie+0x2e2/0x300 fs/fscache/cookie.c:195
__fscache_acquire_cookie fs/fscache/cookie.c:296 [inline]
__fscache_acquire_cookie+0x132/0x380 fs/fscache/cookie.c:257
fscache_acquire_cookie include/linux/fscache.h:334 [inline]
v9fs_cache_session_get_cookie+0x74/0x120 fs/9p/cache.c:60
v9fs_session_init+0x724/0xa90 fs/9p/v9fs.c:471
v9fs_mount+0x56/0x450 fs/9p/vfs_super.c:126
legacy_get_tree+0x2b/0x90 fs/fs_context.c:610
vfs_get_tree+0x28/0x100 fs/super.c:1498
do_new_mount fs/namespace.c:2988 [inline]
path_mount+0xb92/0xfe0 fs/namespace.c:3318
do_mount+0xa1/0xc0 fs/namespace.c:3331
__do_sys_mount fs/namespace.c:3539 [inline]
__se_sys_mount fs/namespace.c:3516 [inline]
__x64_sys_mount+0xf4/0x160 fs/namespace.c:3516
Fix this by moving the list_add_tail before goto statements.
Fixes: 884a76881fc5 ("fscache: Procfile to display cookies")
Signed-off-by: Dongliang Mu <mudongliangabcd@xxxxxxxxx>
---
fs/fscache/cookie.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/fs/fscache/cookie.c b/fs/fscache/cookie.c
index cd42be646ed3..d101e212db74 100644
--- a/fs/fscache/cookie.c
+++ b/fs/fscache/cookie.c
@@ -150,6 +150,11 @@ struct fscache_cookie *fscache_alloc_cookie(
if (!cookie)
return NULL;
+ /* move list_add_tail before any error handling code */
+ write_lock(&fscache_cookies_lock);
+ list_add_tail(&cookie->proc_link, &fscache_cookies);
+ write_unlock(&fscache_cookies_lock);
+
cookie->key_len = index_key_len;
cookie->aux_len = aux_data_len;
@@ -186,9 +191,6 @@ struct fscache_cookie *fscache_alloc_cookie(
* told it may not wait */
INIT_RADIX_TREE(&cookie->stores, GFP_NOFS & ~__GFP_DIRECT_RECLAIM);
- write_lock(&fscache_cookies_lock);
- list_add_tail(&cookie->proc_link, &fscache_cookies);
- write_unlock(&fscache_cookies_lock);
return cookie;
nomem:
--
2.25.1
--
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