netdev - Re: [GIT] Networking

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Date:	Tue, 24 Jun 2014 20:51:39 -0700
From:	Tom Herbert <therbert@...gle.com>
To:	David Miller <davem@...emloft.net>
Cc:	torvalds@...ux-foundation.org, davej@...hat.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Netdev List <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [GIT] Networking

I believe in the no scatter-gather case of  skb_segment is not set
correctly. Will post a patch momentarily.

On Tue, Jun 24, 2014 at 8:05 PM, Tom Herbert <therbert@...gle.com> wrote:
>> tcp_gso_segment() makes sure that the headers are reachable in the linear
>> area with the pskb_may_pull(skb, sizeof(*th)) call, and gso_make_checksum()
>> is only working with the area up to SKB_GSO_CB()->csum_start which should
>> be within this area for sure.
>>
> Seems likely that csum_start is not properly initialized in this path.
> I am thinking that this may have happened in GRO path on a checksum
> error where CHECKSUM_PARTIAL (and hence csum) is not set. That would
> explain the infrequency of the occurrence,  and also previously not
> setting csum would have just resulted in sending a corrupted packet
> not a crash.
>
>> Well, that's the precondition we seem to be relying upon, I suppose an
>> assert is in order.
>
> Assert on SKB_GSO_CB()->csum_start == 0 would confirm my suspicion.
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