netdev - Re: ip_rcv_finish() NULL pointer kernel panic

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Date:   Thu, 26 Jan 2017 17:24:33 +0100
From:   Florian Westphal <fw@...len.de>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Roy Keene <lkml@...ene.org>, netdev@...r.kernel.org,
        netfilter-devel@...r.kernel.org
Subject: Re: ip_rcv_finish() NULL pointer kernel panic

Eric Dumazet <eric.dumazet@...il.com> wrote:
> > Though possibly with different things not setting the "input" function 
> > pointer in the "struct dst_entry".
> > 
> > include/net/dst.h:
> >   496 static inline int dst_input(struct sk_buff *skb) {
> >   498         return skb_dst(skb)->input(skb);
> >   499 }
> > 
> > Is there any reason not to check to see if this pointer is NULL before 
> > blindly calling it ?
> 
> Sure. It can not be NULL at this point.
> 
> Just look at the code in ip_rcv_finish() :
> 
> It first make sure to get a valid dst.
> 
> Something is broken, probably in bridge netfilter code.
> 
> I suspect the dst here points to &br->fake_rtable, and this is not
> expected.
> 
> br_drop_fake_rtable() should have been called somewhere ...

I think it makes sense to set dst->incoming
to a stub in br_netfilter_rtable_init() to just kfree_skb()+
WARN_ON_ONCE(), no need to add code to ip stack or crash kernel
due to brnf bug.