From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jing Xia Subject: [PATCH] mm: memcg: fix use after free in mem_cgroup_iter() Date: Thu, 19 Jul 2018 18:06:47 +0800 Message-ID: <1531994807-25639-1-git-send-email-jing.xia@unisoc.com> Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id; bh=RJhJrPg5vB3sWmzaN5lFkpQiPrD9UBbb70hv06tTUJ4=; b=LGi5d0BhcB4tPQcG26h5D5OhpGUIlojIG4lB+mcxmmVOvO9fCPITFBLoriP8vcRM7W SsWSt7yC/SnEFr/o6aB/TXMiOQmREPLLkqVa5BQFvTDvHSqGJWKSHaGIIoOkVWSwLQe1 KrU0wVvvDtdKlLueIiTTlwC8f9qMVPrqUMQjeYLuW5iTo4fpjHZNHexVbV+EM0LVpTOq uIMpyC1AYUc5TB2AyPETwm+MSx45Xw6DmgVOf4eeZ0KblVQ0eJ01Cl3zaeH6bgLE6HIA JN//NmrgXYw978tqx4SOoLj6fblWI+Afadq0lwGc9HEvu2zDHC5F0Xe7PUecthW5qKvg GJgA== Sender: linux-kernel-owner@vger.kernel.org List-ID: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: hannes@cmpxchg.org, mhocko@kernel.org, vdavydov.dev@gmail.com Cc: chunyan.zhang@unisoc.com, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org 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. Signed-off-by: Jing Xia --- mm/memcontrol.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index e6f0d5e..8c0280b 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -850,7 +850,7 @@ static void invalidate_reclaim_iterators(struct mem_cgroup *dead_memcg) 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++) { -- 1.9.1