linux-kernel - Re: [PATCH] ipv4/mptcp: fix divide error

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Date:   Tue, 24 Aug 2021 15:58:31 +0800
From:   Jiang Biao <benbjiang@...il.com>
To:     Matthieu Baerts <matthieu.baerts@...sares.net>
Cc:     mathew.j.martineau@...ux.intel.com, davem@...emloft.net,
        kuba@...nel.org, netdev@...r.kernel.org, mptcp@...ts.linux.dev,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Jiang Biao <benbjiang@...cent.com>,
        Jiang Biao <tcs_robot@...cent.com>
Subject: Re: [PATCH] ipv4/mptcp: fix divide error

Hi,

On Tue, 24 Aug 2021 at 15:36, Matthieu Baerts
<matthieu.baerts@...sares.net> wrote:
>
> Hi Jiang,
>
> On 24/08/2021 09:19, Jiang Biao wrote:
>
> (...)
>
> > There is a fix divide error reported,
> > divide error: 0000 [#1] PREEMPT SMP KASAN
> > RIP: 0010:tcp_tso_autosize build/../net/ipv4/tcp_output.c:1975 [inline]
> > RIP: 0010:tcp_tso_segs+0x14f/0x250 build/../net/ipv4/tcp_output.c:1992
>
> Thank you for this patch and validating MPTCP on your side!
>
> This issue is actively tracked on our Github project [1] and a patch is
> already in our tree [2] but still under validation.
> > It's introduced by non-initialized info->mss_now in __mptcp_push_pending.
> > Fix it by adding protection in mptcp_push_release.
>
> Indeed, you are right, info->mss_now can be set to 0 in some cases but
> that's not normal.
>
> Instead of adding a protection here, we preferred fixing the root cause,
> see [2]. Do not hesitate to have a look at the other patch and comment
> there if you don't agree with this version.
> Except if [2] is difficult to backport, I think we don't need your extra
> protection. WDYT?
>
Agreed, fixing the root cause is much better.
Thanks for the reply.

Regards,
Jiang