netdev - Re: [PATCH net] tcp: do not underestimate skb->truesize in tcp_trim

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Message-Id: <20170428.160556.2072008893563794166.davem@davemloft.net>
Date:   Fri, 28 Apr 2017 16:05:56 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     andreyknvl@...gle.com
Cc:     eric.dumazet@...il.com, netdev@...r.kernel.org
Subject: Re: [PATCH net] tcp: do not underestimate skb->truesize in
 tcp_trim_head()

From: Andrey Konovalov <andreyknvl@...gle.com>
Date: Thu, 27 Apr 2017 13:49:57 +0200

> On Thu, Apr 27, 2017 at 2:15 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>> From: Eric Dumazet <edumazet@...gle.com>
>>
>> Andrey found a way to trigger the WARN_ON_ONCE(delta < len) in
>> skb_try_coalesce() using syzkaller and a filter attached to a TCP
>> socket over loopback interface.
>>
>> I believe one issue with looped skbs is that tcp_trim_head() can end up
>> producing skb with under estimated truesize.
>>
>> It hardly matters for normal conditions, since packets sent over
>> loopback are never truncated.
>>
>> Bytes trimmed from skb->head should not change skb truesize, since
>> skb->head is not reallocated.
> 
> Hi Eric,
> 
> With all 3 of your patches applied to net-next I don't see the warning any more.
> 
> Thanks!
> 
> Tested-by: Andrey Konovalov <andreyknvl@...gle.com>

Applied and queued up for -stable, thanks Eric.