netdev - Re: Problematic commits in the ipsec tree

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Date:	Thu, 22 Aug 2013 15:53:42 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Steffen Klassert <steffen.klassert@...unet.com>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: Problematic commits in the ipsec tree

On Thu, Aug 22, 2013 at 12:47:24PM +0200, Steffen Klassert wrote:
> Hannes,
> 
> I have two problematic commits from you in the ipsec tree. The first one is:
> 
> commit 0ea9d5e3e (xfrm: introduce helper for safe determination of mtu)
> 
> This breakes pmtu discovery for IPv4 because now we use the device mtu
> instead of the reduced IPsec mtu in xfrm4_tunnel_check_size() if a IPv4
> socket is at the skb.

I am currently testing this following patch. It should restore old behavior
for ipv4 sockets.

diff --git a/include/net/xfrm.h b/include/net/xfrm.h
index ac5b025..65d3529 100644
--- a/include/net/xfrm.h
+++ b/include/net/xfrm.h
@@ -1730,8 +1730,6 @@ static inline int xfrm_skb_dst_mtu(struct sk_buff *skb)
 
 	if (sk && skb->protocol == htons(ETH_P_IPV6))
 		return ip6_skb_dst_mtu(skb);
-	else if (sk && skb->protocol == htons(ETH_P_IP))
-		return ip_skb_dst_mtu(skb);
 	return dst_mtu(skb_dst(skb));
 }
 
Actually I would like to extend this check so that we only take the
dst_mtu(dst->path) in case of IP_PMTUDISC_PROBE. But that would be a
patch for ipsec-next. I was not sure if we always dispatch to xfrm_mtu
in this code-path.

> 
> The second is:
> 
> commit 844d48746 (xfrm: choose protocol family by skb protocol)
> 
> This breaks pmtu discovery for IPv6 too because skb->protocol can be null
> in __xfrm6_output().

I am currently checking if there are side-effects if we set skb->protocol in
raw sockets. This should solve this problem. Btw. this is also the case for
IPv4.

Hope to have tested patches later today.

Thanks,

  Hannes

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