[PATCH 4.16 16/72] memcg: fix per_node_info cleanup

[Greg Kroah-Hartman]

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

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

From: Michal Hocko <mhocko@xxxxxxxx>

commit 4eaf431f6f71bbed40a4c733ffe93a7e8cedf9d9 upstream.

syzbot has triggered a NULL ptr dereference when allocation fault
injection enforces a failure and alloc_mem_cgroup_per_node_info
initializes memcg->nodeinfo only half way through.

But __mem_cgroup_free still tries to free all per-node data and
dereferences pn->lruvec_stat_cpu unconditioanlly even if the specific
per-node data hasn't been initialized.

The bug is quite unlikely to hit because small allocations do not fail
and we would need quite some numa nodes to make struct
mem_cgroup_per_node large enough to cross the costly order.

Link: http://lkml.kernel.org/r/20180406100906.17790-1-mhocko@xxxxxxxxxx
Reported-by: syzbot+8a5de3cce7cdc70e9ebe@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 00f3ca2c2d66 ("mm: memcontrol: per-lruvec stats infrastructure")
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
Reviewed-by: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
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 |    3 +++
 1 file changed, 3 insertions(+)

--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4108,6 +4108,9 @@ static void free_mem_cgroup_per_node_inf
 {
 	struct mem_cgroup_per_node *pn = memcg->nodeinfo[node];
 
+	if (!pn)
+		return;
+
 	free_percpu(pn->lruvec_stat_cpu);
 	kfree(pn);
 }