netdev - Re: [GIT] Networking

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Message-ID: <CA+mtBx8F3XPU5bLfKc046Oz8thp50FZadLfAAfe-Hw2HU9sjsA@mail.gmail.com>
Date:	Tue, 24 Jun 2014 20:05:30 -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

> 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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