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Date:	Thu, 12 May 2016 09:51:24 -0700
From:	Alexander Duyck <>
To:	Eric Dumazet <>
Cc:	Alexander Duyck <>,
	Netdev <>,
	David Miller <>,
	Tom Herbert <>
Subject: Re: [net-next PATCH] udp: Resolve NULL pointer dereference

On Wed, May 11, 2016 at 8:43 PM, Eric Dumazet <> wrote:
> On Wed, 2016-05-11 at 19:24 -0700, Alexander Duyck wrote:
>> While testing an OpenStack configuration using VXLANs I saw the following
>> call trace:
>> I believe the trace is pointing to the call to dev_net(dev) in
>> udp4_lib_lookup_skb.  If I am not mistaken I believe it is possible for us
>> to have skb_dst(skb)->dev be NULL.  So to resolve that I am adding a check
>> for this case and skipping the assignment if such an event occurs.
> skb_dst(skb)->dev can be NULL ???

That is what appears to be happening.  Though I can do some more
research into this.

> Why only UDP ipv4 would need a fix, and not ipv6 ?

Yeah, I should probably fix IPv6 as well if there is an issue.

> Looks the bug is somewhere else maybe ?

I was thinking about it last night and I am not certain we should even
see skb_dst(skb) set as Cong mentioned.  I'm wondering if I should
update the code to just use skb->dev because these functions are
currently only used in the GRO path anyway so it isn't as if skb_dst
should be populated.

- Alex

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