Re: [PATCH v2 1/1] xfrm: Use actual socket sk instead of skb socket for xfrm_output_resume

[Steffen Klassert]

On Tue, Mar 02, 2021 at 08:00:04AM +1300, Evan Nimmo wrote:
> A situation can occur where the interface bound to the sk is different
> to the interface bound to the sk attached to the skb. The interface
> bound to the sk is the correct one however this information is lost inside
> xfrm_output2 and instead the sk on the skb is used in xfrm_output_resume
> instead. This assumes that the sk bound interface and the bound interface
> attached to the sk within the skb are the same which can lead to lookup
> failures inside ip_route_me_harder resulting in the packet being dropped.
> 
> We have an l2tp v3 tunnel with ipsec protection. The tunnel is in the
> global VRF however we have an encapsulated dot1q tunnel interface that
> is within a different VRF. We also have a mangle rule that marks the 
> packets causing them to be processed inside ip_route_me_harder.
> 
> Prior to commit 31c70d5956fc ("l2tp: keep original skb ownership") this
> worked fine as the sk attached to the skb was changed from the dot1q
> encapsulated interface to the sk for the tunnel which meant the interface
> bound to the sk and the interface bound to the skb were identical.
> Commit 46d6c5ae953c ("netfilter: use actual socket sk rather than skb sk
> when routing harder") fixed some of these issues however a similar
> problem existed in the xfrm code.
> 
> Fixes: 31c70d5956fc ("l2tp: keep original skb ownership")
> 
> Signed-off-by: Evan Nimmo <evan.nimmo@xxxxxxxxxxxxxxxxxxx>

Applied, thanks Evan!