The patch titled
Subject: mm: memcg/slab: fix use after free in obj_cgroup_charge
has been removed from the -mm tree. Its filename was
mm-memcg-slab-fix-use-after-free-in-obj_cgroup_charge.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
From: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Subject: mm: memcg/slab: fix use after free in obj_cgroup_charge
The rcu_read_lock/unlock only can guarantee that the memcg will not be
freed, but it cannot guarantee the success of css_get to memcg.
If the whole process of a cgroup offlining is completed between reading a
objcg->memcg pointer and bumping the css reference on another CPU, and
there are exactly 0 external references to this memory cgroup (how we get
to the obj_cgroup_charge() then?), css_get() can change the ref counter
from 0 back to 1.
Link: https://lkml.kernel.org/r/20201028035013.99711-2-songmuchun@xxxxxxxxxxxxx
Fixes: bf4f059954dc ("mm: memcg/slab: obj_cgroup API")
Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Acked-by: Roman Gushchin <guro@xxxxxx>
Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Yafang Shao <laoar.shao@xxxxxxxxx>
Cc: Chris Down <chris@xxxxxxxxxxxxxx>
Cc: Christian Brauner <christian.brauner@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memcontrol.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
--- a/mm/memcontrol.c~mm-memcg-slab-fix-use-after-free-in-obj_cgroup_charge
+++ a/mm/memcontrol.c
@@ -3235,8 +3235,10 @@ int obj_cgroup_charge(struct obj_cgroup
* independently later.
*/
rcu_read_lock();
+retry:
memcg = obj_cgroup_memcg(objcg);
- css_get(&memcg->css);
+ if (unlikely(!css_tryget(&memcg->css)))
+ goto retry;
rcu_read_unlock();
nr_pages = size >> PAGE_SHIFT;
_
Patches currently in -mm which might be from songmuchun@xxxxxxxxxxxxx are
