4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jing Xia <jing.xia.mail@xxxxxxxxx> 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@xxxxxxxxxx Fixes: 6df38689e0e9 ("mm: memcontrol: fix possible memcg leak due to interrupted reclaim") Signed-off-by: Jing Xia <jing.xia.mail@xxxxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx> Cc: <chunyan.zhang@xxxxxxxxxx> Cc: Shakeel Butt <shakeelb@xxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- mm/memcontrol.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -996,7 +996,7 @@ static void invalidate_reclaim_iterators int nid, zid; int i; - while ((memcg = parent_mem_cgroup(memcg))) { + for (; memcg; memcg = parent_mem_cgroup(memcg)) { for_each_node(nid) { for (zid = 0; zid < MAX_NR_ZONES; zid++) { mz = &memcg->nodeinfo[nid]->zoneinfo[zid];