linux-kernel - Re: [PATCH -next] hugetlb_cgroup: fix illegal access to memory

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Message-ID: <20200324182454.GE162390@mtj.duckdns.org>
Date:   Tue, 24 Mar 2020 14:24:54 -0400
From:   Tejun Heo <tj@...nel.org>
To:     Mina Almasry <almasrymina@...gle.com>
Cc:     syzbot+cac0c4e204952cf449b1@...kaller.appspotmail.com,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Giuseppe Scrivano <gscrivan@...hat.com>,
        mike.kravetz@...cle.com, rientjes@...gle.com
Subject: Re: [PATCH -next] hugetlb_cgroup: fix illegal access to memory

On Fri, Mar 13, 2020 at 03:39:20PM -0700, Mina Almasry wrote:
> This appears to be a mistake in commit faced7e0806cf ("mm: hugetlb
> controller for cgroups v2"). Essentially that commit does
> a hugetlb_cgroup_from_counter assuming that page_counter_try_charge has
> initialized counter, but if page_counter_try_charge has failed then it
> seems it does not initialize counter, so
> hugetlb_cgroup_from_counter(counter) ends up pointing to random memory,
> causing kasan to complain.
> 
> Solution, simply use h_cg, instead of
> hugetlb_cgroup_from_counter(counter), since that is a reference to the
> hugetlb_cgroup anyway. After this change kasan ceases to complain.
> 
> Signed-off-by: Mina Almasry <almasrymina@...gle.com>
> Reported-by: syzbot+cac0c4e204952cf449b1@...kaller.appspotmail.com
> Fixes: commit faced7e0806cf ("mm: hugetlb controller for cgroups v2")
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: linux-mm@...ck.org
> Cc: linux-kernel@...r.kernel.org
> Cc: Giuseppe Scrivano <gscrivan@...hat.com>
> Cc: Tejun Heo <tj@...nel.org>
> Cc: mike.kravetz@...cle.com
> Cc: rientjes@...gle.com

Acked-by: Tejun Heo <tj@...nel.org>

Thanks.

-- 
tejun