netdev - Re: [PATCH] ip_forward: Drop frames with attached skb->sk

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Message-ID: <1429012487.7346.3.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Tue, 14 Apr 2015 04:54:47 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Sebastian Poehn <sebastian.poehn@...il.com>
Cc:	yzhu1 <Yanjun.Zhu@...driver.com>,
	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	fw@...len.de
Subject: Re: [PATCH] ip_forward: Drop frames with attached skb->sk

On Tue, 2015-04-14 at 08:40 +0200, Sebastian Poehn wrote:
> On Tue, 2015-04-14 at 14:33 +0800, yzhu1 wrote:
> > On 04/14/2015 01:52 PM, Sebastian Poehn wrote:
> > > Initial discussion was:
> > > [FYI] xfrm: Don't lookup sk_policy for timewait sockets
> > >
> > > Forwarded frames should not have a socket attached. Especially
> > > tw sockets will lead to panics later-on in the stack.
> > >
> > > This was observed with TPROXY assigning a tw socket and broken
> > > policy routing (misconfigured). As a result frame enters
> > > forwarding path instead of input. We cannot solve this in
> > > TPROXY as it cannot know that policy routing is broken.
> > >
> > > Signed-off-by: Sebastian Poehn <sebastian.poehn@...il.com>
> > > ---
> > > diff --git a/net/ipv4/ip_forward.c b/net/ipv4/ip_forward.c
> > > index 939992c..2fc3b3e 100644
> > > --- a/net/ipv4/ip_forward.c
> > > +++ b/net/ipv4/ip_forward.c
> > > @@ -82,6 +82,10 @@ int ip_forward(struct sk_buff *skb)
> > >   	if (skb->pkt_type != PACKET_HOST)
> > >   		goto drop;
> > >   
> > > +	/* this should happen neither */
> > Sorry. "neither" should be "either"?
> 
>         /* that should never happen */
>         if (skb->pkt_type != PACKET_HOST)
>                 goto drop;
> 
>         /* this should happen neither */
>         if (unlikely(skb->sk))
>                 goto drop;
> 
> Both of them should never happen.

I do not feel the comment is useful in this form.

I would prefer explicit TPROXY reference, maybe using this :

#if IS_ENABLED(CONFIG_NETFILTER_XT_TARGET_TPROXY)
	if (skb->sk)
		goto drop;
#endif

changelog will precisely describes the problem for the curious readers.

Thanks !


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