netdev - Re: [RFC] net: remove erroneous sk null assignment in timestamping

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Message-Id: <20111007.133356.489094996618032061.davem@davemloft.net>
Date:	Fri, 07 Oct 2011 13:33:56 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	johannes@...solutions.net
Cc:	netdev@...r.kernel.org, richardcochran@...il.com
Subject: Re: [RFC] net: remove erroneous sk null assignment in timestamping

From: Johannes Berg <johannes@...solutions.net>
Date: Fri, 07 Oct 2011 19:11:41 +0200

> From: Johannes Berg <johannes.berg@...el.com>
> 
> skb->sk is obviously required to be non-NULL
> when we get into skb_complete_tx_timestamp().
> sock_queue_err_skb() will call skb_orphan()
> first thing which sets skb->sk = NULL itself.
> This may crash if the skb is still charged to
> the socket (skb->destructor is sk_wfree).
> 
> The assignment here thus seems to not only be
> pointless (due to the skb_orphan() call) but
> also dangerous (due to the crash).
> 
> Signed-off-by: Johannes Berg <johannes.berg@...el.com>

It looks like skb_clone_tx_timestamp() sets clone->sk without any
proper refcounting, so I bet this NULL'ing it out is working
around that bug.

The TX side of this infrastructure seems very poorly tested.
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