netdev - Re: Bug in computing data_len in tcp

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Date:	Fri, 02 Dec 2011 17:05:35 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Vijay Subramanian <subramanian.vijay@...il.com>
Cc:	Tom Herbert <therbert@...gle.com>,
	Linux Netdev List <netdev@...r.kernel.org>,
	David Miller <davem@...emloft.net>
Subject: Re: Bug in computing data_len in tcp_sendmsg?

Le vendredi 02 décembre 2011 à 16:44 +0100, Eric Dumazet a écrit :

> [PATCH net-next] tcp: fix tcp_trim_head()
> 
> commit f07d960df3 (tcp: avoid frag allocation for small frames)
> breaked assumption in tcp stack that skb is either linear (data_len ==
> 0), either fully fragged (data_len == len)
> 
> Thanks to Vijay for providing a very detailed explanation.
> 
> Reported-by: Vijay Subramanian <subramanian.vijay@...il.com>
> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
> ---

Another problem is the possible misalignement of skb->data if/when we
receive an ACK of an odd (not a 4 multiple) tcp sequence.

So when/if packet is restransmited, tcp header (and IP header as well)
could be misaligned.

Hmm, I probably miss something obvious, since this problem could happen
for linear skbs before my patch ?



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