netdev - Re: [PATCH 1/2] tcp: must unclone packets before mangling them

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Date:	Thu, 17 Oct 2013 16:08:53 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	netdev@...r.kernel.org, ncardwell@...gle.com, ycheng@...gle.com
Subject: Re: [PATCH 1/2] tcp: must unclone packets before mangling them

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Tue, 15 Oct 2013 11:54:30 -0700

> From: Eric Dumazet <edumazet@...gle.com>
> 
> TCP stack should make sure it owns skbs before mangling them.
> 
> We had various crashes using bnx2x, and it turned out gso_size
> was cleared right before bnx2x driver was populating TC descriptor
> of the _previous_ packet send. TCP stack can sometime retransmit
> packets that are still in Qdisc.
> 
> Of course we could make bnx2x driver more robust (using
> ACCESS_ONCE(shinfo->gso_size) for example), but the bug is TCP stack.
> 
> We have identified two points where skb_unclone() was needed.
> 
> This patch adds a WARN_ON_ONCE() to warn us if we missed another
> fix of this kind.
> 
> Kudos to Neal for finding the root cause of this bug. Its visible
> using small MSS.
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Signed-off-by: Neal Cardwell <ncardwell@...gle.com>
> Cc: Yuchung Cheng <ycheng@...gle.com>

Applied and queued up for -stable.
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