[Devel] [PATCH RHEL7 COMMIT] ms/mm/list_lru.c: avoid error-path NULL pointer deref

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-514.16.1.vz7.32.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-514.16.1.vz7.32.10
------>
commit 1046b412a99fd5e0b7570e58d80bac360d971a15
Author: Alexander Polakov <apolyakov at beget.ru>
Date:   Tue Jun 20 20:42:53 2017 +0400

    ms/mm/list_lru.c: avoid error-path NULL pointer deref
    
    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 909eca2..84b4c21 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;
 	}