netdev - Re: [BUG] skb corruption and kernel panic at forwarding with fragmentation

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Message-ID: <20160107120339.GC23789@breakpoint.cc>
Date:	Thu, 7 Jan 2016 13:03:39 +0100
From:	Florian Westphal <fw@...len.de>
To:	Konstantin Khlebnikov <koct9i@...il.com>
Cc:	Florian Westphal <fw@...len.de>,
	Thadeu Lima de Souza Cascardo <cascardo@...hat.com>,
	Cong Wang <xiyou.wangcong@...il.com>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	David Miller <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [BUG] skb corruption and kernel panic at forwarding with
 fragmentation

Konstantin Khlebnikov <koct9i@...il.com> wrote:
> On Thu, Jan 7, 2016 at 2:49 AM, Florian Westphal <fw@...len.de> wrote:
> > ... but it seems that those three are the only affected callers
> > of skb_gso_segment (tbf is ok since skb isn't owned by anyone,
> > ovs does save/restore already).
> >
> > I think this patch is the right way, we just need similar
> > save/restore in nfqnl_enqueue_packet and xfrm_output_gso().
> 
> Which CB could be here? at this point skb isn't owned by netlink yet.

inet(6)_skb_parm, nfqnl_enqueue_packet is called via netfilter hooks, skb
is owned by ipv4 or ipv6 stack.

> > The latter two can be used by either ipv4 or ipv6 so it might
> > be preferable to just save/restore sizeof(struct skb_gso_cb);
> > or a union of inet_skb_parm+inet6_skb_parm.
> 
> Or just shift GSO CB and add couple checks like
> BUILD_BUG_ON(sizeof(SKB_GSO_CB(skb)->room) < sizeof(*IPCB(skb)));

Right, that works too.
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