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Date:   Thu, 10 Oct 2019 09:19:37 +0200
From:   Michal Hocko <mhocko@kernel.org>
To:     Yizhuo Zhai <yzhai003@ucr.edu>
Cc:     Johannes Weiner <hannes@cmpxchg.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        cgroups@vger.kernel.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, Zhiyun Qian <zhiyunq@cs.ucr.edu>,
        Chengyu Song <csong@cs.ucr.edu>
Subject: Re: Potential NULL pointer deference in mm/memcontrol.c
Message-ID: <20191010071937.GA18412@dhcp22.suse.cz>
References: <CABvMjLRgShsBiod+GVcqirmKeFLN_KfxdDDwGo22YK0wULepwA@mail.gmail.com>
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On Wed 09-10-19 21:56:04, Yizhuo Zhai wrote:
> Hi All:
> mm/memcontrol.c:
> The function mem_cgroup_from_css() could return NULL, but some callers

This is the case only when the memory cgroup controller is disabled
which is a boot time option.

> in this file
> checks the return value but directly dereference it, which seems
> potentially unsafe.
> Such callers include mem_cgroup_hierarchy_read(),
> mem_cgroup_hierarchy_write(), mem_cgroup_read_u64(),
> mem_cgroup_reset(), etc.

And none of those should be ever called under that condition AFAICS.

Thanks!
-- 
Michal Hocko
SUSE Labs