[CC Andrew]
On Thu 19-07-18 18:06:47, Jing Xia wrote:
> 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.
Well, spotted!
I suspect
Fixes: 6df38689e0e9 ("mm: memcontrol: fix possible memcg leak due to interrupted reclaim")
but maybe it goes further into past. I also suggest
Cc: stable
even though the non-hierarchical mode is strongly discouraged. A lack of
reports for 3 years is encouraging that not many people really use this
mode.
> Signed-off-by: Jing Xia <jing.xia.mail@xxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Thanks!
> ---
> 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
--
Michal Hocko
SUSE Labs
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