Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:60446 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728214AbeGUBoc (ORCPT ); Fri, 20 Jul 2018 21:44:32 -0400 Date: Fri, 20 Jul 2018 17:53:48 -0700 From: akpm@linux-foundation.org To: vdavydov.dev@gmail.com, stable@vger.kernel.org, shakeelb@google.com, mhocko@suse.com, hannes@cmpxchg.org, chunyan.zhang@unisoc.com, jing.xia.mail@gmail.com, akpm@linux-foundation.org, mm-commits@vger.kernel.org, torvalds@linux-foundation.org Subject: [patch 6/6] mm: memcg: fix use after free in mem_cgroup_iter() Message-ID: <20180721005348.9KKGu%akpm@linux-foundation.org> Sender: stable-owner@vger.kernel.org List-ID: From: Jing Xia Subject: mm: memcg: fix use after free in mem_cgroup_iter() It was reported that a kernel crash happened in mem_cgroup_iter(), which can be triggered if the legacy cgroup-v1 non-hierarchical mode is used. Unable to handle kernel paging request at virtual address 6b6b6b6b6b6b8f ...... Call trace: mem_cgroup_iter+0x2e0/0x6d4 shrink_zone+0x8c/0x324 balance_pgdat+0x450/0x640 kswapd+0x130/0x4b8 kthread+0xe8/0xfc ret_from_fork+0x10/0x20 mem_cgroup_iter(): ...... if (css_tryget(css)) <-- crash here break; ...... The crashing reason is that mem_cgroup_iter() uses the memcg object whose pointer is stored in iter->position, which has been freed before and filled with POISON_FREE(0x6b). And the root cause of the use-after-free issue is that invalidate_reclaim_iterators() fails to reset the value of iter->position to NULL when the css of the memcg is released in non- hierarchical mode. Link: http://lkml.kernel.org/r/1531994807-25639-1-git-send-email-jing.xia@unisoc.com Fixes: 6df38689e0e9 ("mm: memcontrol: fix possible memcg leak due to interrupted reclaim") Signed-off-by: Jing Xia Acked-by: Michal Hocko Cc: Johannes Weiner Cc: Vladimir Davydov Cc: Cc: Shakeel Butt Cc: Signed-off-by: Andrew Morton --- mm/memcontrol.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff -puN mm/memcontrol.c~mm-memcg-fix-use-after-free-in-mem_cgroup_iter mm/memcontrol.c --- a/mm/memcontrol.c~mm-memcg-fix-use-after-free-in-mem_cgroup_iter +++ a/mm/memcontrol.c @@ -850,7 +850,7 @@ static void invalidate_reclaim_iterators int nid; int i; - while ((memcg = parent_mem_cgroup(memcg))) { + for (; memcg; memcg = parent_mem_cgroup(memcg)) { for_each_node(nid) { mz = mem_cgroup_nodeinfo(memcg, nid); for (i = 0; i <= DEF_PRIORITY; i++) { _