netdev - Re: net: Fix skb csum races when peeking

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Date:	Wed, 15 Jul 2015 16:14:13 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	herbert@...dor.apana.org.au
Cc:	edumazet@...gle.com, eric.dumazet@...il.com,
	khlebnikov@...dex-team.ru, netdev@...r.kernel.org
Subject: Re: net: Fix skb csum races when peeking

From: Herbert Xu <herbert@...dor.apana.org.au>
Date: Mon, 13 Jul 2015 20:01:42 +0800

> When we calculate the checksum on the recv path, we store the
> result in the skb as an optimisation in case we need the checksum
> again down the line.
> 
> This is in fact bogus for the MSG_PEEK case as this is done without
> any locking.  So multiple threads can peek and then store the result
> to the same skb, potentially resulting in bogus skb states.
> 
> This patch fixes this by only storing the result if the skb is not
> shared.  This preserves the optimisations for the few cases where
> it can be done safely due to locking or other reasons, e.g., SIOCINQ.
> 
> Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>

Also applied and queued up for -stable, thanks!
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