linux-kernel - Re: [PATCH] cgroup1: fix leaked context root causing sporadic NULL deref in LTP

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Date:   Wed, 16 Jun 2021 11:23:34 -0400
From:   Tejun Heo <tj@...nel.org>
To:     Paul Gortmaker <paul.gortmaker@...driver.com>
Cc:     linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
        Al Viro <viro@...iv.linux.org.uk>,
        Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>, stable@...r.kernel.org,
        Richard Purdie <richard.purdie@...uxfoundation.org>
Subject: Re: [PATCH] cgroup1: fix leaked context root causing sporadic NULL
 deref in LTP

Hello,

On Wed, Jun 16, 2021 at 08:51:57AM -0400, Paul Gortmaker wrote:
> A fix would be to not leave the stale reference in fc->root as follows:
> 
>    --------------
>                   dput(fc->root);
>   +               fc->root = NULL;
>                   deactivate_locked_super(sb);
>    --------------
> 
> ...but then we are just open-coding a duplicate of fc_drop_locked() so we
> simply use that instead.

As this is unlikely to be a real-world problem both in probability and
circumstances, I'm applying this to cgroup/for-5.14 instead of
cgroup/for-5.13-fixes.

Thanks.

-- 
tejun