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From: David Miller <davem@davemloft.net>
Subject: Re: [PATCH] tcp: take care of misalignments
Date: Sun, 04 Dec 2011 13:21:26 -0500 (EST)
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From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Sun, 04 Dec 2011 08:39:53 +0100

> [PATCH] tcp: take care of misalignments
> 
> We discovered that TCP stack could retransmit misaligned skbs if a
> malicious peer acknowledged sub MSS frame. This currently can happen
> only if output interface is non SG enabled : If SG is enabled, tcp
> builds headless skbs (all payload is included in fragments), so the tcp
> trimming process only removes parts of skb fragments, header stay
> aligned.
> 
> Some arches cant handle misalignments, so force a head reallocation and
> shrink headroom to MAX_TCP_HEADER.
> 
> Dont care about misaligments on x86 and PPC (or other arches setting
> NET_IP_ALIGN to 0)
> 
> This patch introduces __pskb_copy() which can specify the headroom of
> new head, and pskb_copy() becomes a wrapper on top of __pskb_copy()
> 
> Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>

Looks good, applied.