Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Thu, 30 Sep 2021 15:06:40 +0200
From:   Alexey Gladkov <legion@kernel.org>
To:     Jordan Glover <Golden_Miller83@protonmail.ch>
Cc:     ebiederm@xmission.com, LKML <linux-kernel@vger.kernel.org>,
        linux-mm@kvack.org, containers@lists.linux-foundation.org,
        Yu Zhao <yuzhao@google.com>
Subject: Re: linux 5.14.3: free_user_ns causes NULL pointer dereference
Message-ID: <20210930130640.wudkpmn3cmah2cjz@example.org>
References: <1M9_d6wrcu6rdPe1ON0_k0lOxJMyyot3KAb1gdyuwzDPC777XVUWPHoTCEVmcK3fYfgu7sIo3PSaLe9KulUdm4TWVuqlbKyYGxRAjsf_Cpk=@protonmail.ch>
 <87ee9pa6xw.fsf@disp2133>
 <OJK-F2NSBlem52GqvCQYzaVxs2x9Csq3qO4QbTG4A4UUNaQpebpAQmyyKzUd70CIo27C4K7CL3bhIzcxulIzYMu067QOMXCFz8ejh3ZtFhE=@protonmail.ch>
 <U6ByMUZ9LgvxXX6eb0M9aBx8cw8GpgE1qU22LaxaJ_2bOdnGLLJHDgnLL-6cJT7dKdcG_Ms37APSutc3EIMmtpgpP_2kotVLCNRoUq-wTJ8=@protonmail.ch>
 <878rzw77i3.fsf@disp2133>
 <o3tuBB58KUQjyQsALqWi0s1tSPlgVPST4PNNjHewIgRB7CUOOVyFSFxSBLCOJdUH3ly21cIjBthNyqQGnDgJD7fjU8NiVHq7i0JcMvYuzUA=@protonmail.ch>
 <20210929173611.fo5traia77o63gpw@example.org>
 <hPgvCJ2KbKeauk78uWJEsuKJ5VfMqknPJ_oyOZe6M78-6eG7qnj0t0UKC-joPVowo_nOikIsEWP-ZDioARfI-Cl6zrHjCHPJST3drpi5ALE=@protonmail.ch>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <hPgvCJ2KbKeauk78uWJEsuKJ5VfMqknPJ_oyOZe6M78-6eG7qnj0t0UKC-joPVowo_nOikIsEWP-ZDioARfI-Cl6zrHjCHPJST3drpi5ALE=@protonmail.ch>
Precedence: bulk

On Wed, Sep 29, 2021 at 09:39:06PM +0000, Jordan Glover wrote:
> > I'm still investigating, but I would like to rule out one option.
> >
> > Could you check out the patch?
> 
> 
> Thx, I added it to my kernel and will report in few days.
> Does this patch try to fix the issue or make it easier to track?

I suspect the error is caused by a race between allow_ucounts() and
put_ucounts(). I think this patch could solve the problem.

-- 
Rgrds, legion