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From:   Yizhuo <yzhai003@ucr.edu>
Cc:     csong@cs.ucr.edu, zhiyunq@cs.ucr.edu, Yizhuo <yzhai003@ucr.edu>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        cgroups@vger.kernel.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: [PATCH] mm/memcg: return value of the function mem_cgroup_from_css() is not checked
Date:   Wed, 21 Aug 2019 23:22:09 -0700
Message-Id: <20190822062210.18649-1-yzhai003@ucr.edu>
To:     unlisted-recipients:; (no To-header on input)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Inside function mem_cgroup_wb_domain(), the pointer memcg
could be NULL via mem_cgroup_from_css(). However, this pointer is
not checked and directly dereferenced in the if statement,
which is potentially unsafe.

Signed-off-by: Yizhuo <yzhai003@ucr.edu>
---
 mm/memcontrol.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 661f046ad318..bd84bdaed3b0 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3665,7 +3665,7 @@ struct wb_domain *mem_cgroup_wb_domain(struct bdi_writeback *wb)
 {
 	struct mem_cgroup *memcg = mem_cgroup_from_css(wb->memcg_css);
 
-	if (!memcg->css.parent)
+	if (!memcg || !memcg->css.parent)
 		return NULL;
 
 	return &memcg->cgwb_domain;
-- 
2.17.1