[Devel] [PATCH rh7] ms/mm/list_lru.c: avoid error-path NULL pointer deref

[Andrey Ryabinin]

From: Alexander Polakov <apolyakov at beget.ru>

commit 1bc11d70b5db7c6bb1414b283d7f09b1fe1ac0d0 upsteram.

As described in https://bugzilla.kernel.org/show_bug.cgi?id=177821:

After some analysis it seems to be that the problem is in alloc_super().
In case list_lru_init_memcg() fails it goes into destroy_super(), which
calls list_lru_destroy().

And in list_lru_init() we see that in case memcg_init_list_lru() fails,
lru->node is freed, but not set NULL, which then leads list_lru_destroy()
to believe it is initialized and call memcg_destroy_list_lru().
memcg_destroy_list_lru() in turn can access lru->node[i].memcg_lrus,
which is NULL.

[akpm at linux-foundation.org: add comment]
Signed-off-by: Alexander Polakov <apolyakov at beget.ru>
Acked-by: Vladimir Davydov <vdavydov.dev at gmail.com>
Cc: Al Viro <viro at zeniv.linux.org.uk>
Cc: <stable at vger.kernel.org>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>

https://jira.sw.ru/browse/PSBM-67300
Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
---
 mm/list_lru.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/list_lru.c b/mm/list_lru.c
index 909eca2c820e..84b4c21d78d7 100644
--- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -532,6 +532,8 @@ int __list_lru_init(struct list_lru *lru, bool memcg_aware,
 	err = memcg_init_list_lru(lru, memcg_aware);
 	if (err) {
 		kfree(lru->node);
+		/* Do this so a list_lru_destroy() doesn't crash: */
+		lru->node = NULL;
 		goto out;
 	}
 
-- 
2.13.0