netdev - Re: [PATCH net] ptp: annotate data-race around q->head and q->tail

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Message-ID: <CANn89iL5NC4-auwBRAitOiGMEk1Ewo9LOu2TitYHnU3ekzAaeA@mail.gmail.com>
Date: Fri, 10 Nov 2023 10:42:01 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Richard Cochran <richardcochran@...il.com>
Cc: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org, eric.dumazet@...il.com
Subject: Re: [PATCH net] ptp: annotate data-race around q->head and q->tail

On Fri, Nov 10, 2023 at 5:23 AM Richard Cochran
<richardcochran@...il.com> wrote:
>
> On Thu, Nov 09, 2023 at 05:48:59PM +0000, Eric Dumazet wrote:
> > As I was working on a syzbot report, I found that KCSAN would
> > probably complain that reading q->head or q->tail without
> > barriers could lead to invalid results.
> >
> > Add corresponding READ_ONCE() and WRITE_ONCE() to avoid
> > load-store tearing.
>
> Acked-by: Richard Cochran <richardcochran@...il.com>

Note the syzbot report I am looking at point to bugs added in

commit 8f5de6fb245326704f37d91780b9a10253a8a100    ptp: support
multiple timestamp event readers

For instance ptp_poll() can crash.

I saw the following patch being merged (without me being CC ?)

commit 8a4f030dbced6fc255cbe67b2d0a129947e18493
Author: Yuran Pereira <yuran.pereira@...mail.com>
Date:   Wed Nov 8 02:18:36 2023 +0530

    ptp: Fixes a null pointer dereference in ptp_ioctl

I do not see how races are solved... Shouldn't
pccontext->private_clkdata be protected by RCU ?