linux-kernel - [PATCH 4.9 09/28] mm: memcg: fix use after free in mem_cgroup

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Message-Id: <20180723122425.846337486@linuxfoundation.org>
Date:   Mon, 23 Jul 2018 14:25:09 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Jing Xia <jing.xia.mail@...il.com>,
        Michal Hocko <mhocko@...e.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        chunyan.zhang@...soc.com, Shakeel Butt <shakeelb@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 4.9 09/28] mm: memcg: fix use after free in mem_cgroup_iter()

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jing Xia <jing.xia.mail@...il.com>

commit 9f15bde671355c351cf20d9f879004b234353100 upstream.

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 <jing.xia.mail@...il.com>
Acked-by: Michal Hocko <mhocko@...e.com>
Cc: Johannes Weiner <hannes@...xchg.org>
Cc: Vladimir Davydov <vdavydov.dev@...il.com>
Cc: <chunyan.zhang@...soc.com>
Cc: Shakeel Butt <shakeelb@...gle.com>
Cc: <stable@...r.kernel.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 mm/memcontrol.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -895,7 +895,7 @@ 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++) {