netdev - Re: [PATCH net-next] tc: fix tc actions in case of shared skb

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Message-Id: <20150711.212917.1463596559900301434.davem@davemloft.net>
Date:	Sat, 11 Jul 2015 21:29:17 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	ast@...mgrid.com
Cc:	jhs@...atatu.com, daniel@...earbox.net, jiri@...nulli.us,
	netdev@...r.kernel.org
Subject: Re: [PATCH net-next] tc: fix tc actions in case of shared skb

From: Alexei Starovoitov <ast@...mgrid.com>
Date: Fri, 10 Jul 2015 17:10:11 -0700

> TC actions need to check for very unlikely event skb->users != 1,
> otherwise subsequent pskb_may_pull/pskb_expand_head will crash.
> When skb_shared() just drop the packet, since in the middle of actions
> it's too late to call skb_share_check(), since classifiers/actions assume
> the same skb pointer.
> 
> Signed-off-by: Alexei Starovoitov <ast@...mgrid.com>

I think whatever creates this skb->users != 1 situation should be fixed,
they should clone the packet.

In fact, it would really help enormously if you could explain in detail
how this situation can actually arise.  Especially since I do not consider
it acceptable to drop the packet in this situation.

Thanks.
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