From: Jing Xia jing.xia.mail@gmail.com 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.c... Fixes: 6df38689e0e9 ("mm: memcontrol: fix possible memcg leak due to interrupted reclaim") Signed-off-by: Jing Xia jing.xia.mail@gmail.com Acked-by: Michal Hocko mhocko@suse.com Cc: Johannes Weiner hannes@cmpxchg.org Cc: Vladimir Davydov vdavydov.dev@gmail.com Cc: chunyan.zhang@unisoc.com Cc: Shakeel Butt shakeelb@google.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

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++) { _