linux-kernel - [PATCH v2] mm: memcg/slab: Fix use after free in obj_cgroup

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20201028035013.99711-2-songmuchun@bytedance.com>
Date:   Wed, 28 Oct 2020 11:50:11 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     hannes@...xchg.org, mhocko@...nel.org, vdavydov.dev@...il.com,
        akpm@...ux-foundation.org, shakeelb@...gle.com, guro@...com,
        iamjoonsoo.kim@....com, laoar.shao@...il.com, chris@...isdown.name,
        christian.brauner@...ntu.com, peterz@...radead.org,
        mingo@...nel.org, keescook@...omium.org, tglx@...utronix.de,
        esyr@...hat.com, surenb@...gle.com, areber@...hat.com,
        elver@...gle.com
Cc:     linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
        linux-mm@...ck.org, Muchun Song <songmuchun@...edance.com>
Subject: [PATCH v2] 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.

Fixes: bf4f059954dc ("mm: memcg/slab: obj_cgroup API")
Signed-off-by: Muchun Song <songmuchun@...edance.com>
Acked-by: Roman Gushchin <guro@...com>
---
 changelog in v2:
 1. Add unlikely and update the commit log suggested by Roman.

 mm/memcontrol.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 8c8b4c3ed5a0..d9cdf899c6fc 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3221,8 +3221,10 @@ int obj_cgroup_charge(struct obj_cgroup *objcg, gfp_t gfp, size_t size)
 	 * 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;
-- 
2.20.1