[PATCH ipsec] vti6: fix PMTU caching and reporting on xmit

[PATCH ipsec] vti6: fix PMTU caching and reporting on xmit

[Eyal Birger]

When setting the skb->dst before doing the MTU check, the route PMTU
caching and reporting is done on the new dst which is about to be
released.

Instead, PMTU handling should be done using the original dst.

This is aligned with IPv4 VTI.

Signed-off-by: Eyal Birger <eyal.birger@gmail.com>
Fixes: ccd740cbc6 ("vti6: Add pmtu handling to vti6_xmit.")
---
 net/ipv6/ip6_vti.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/net/ipv6/ip6_vti.c b/net/ipv6/ip6_vti.c
index ca957dd..e675ec7 100644
--- a/net/ipv6/ip6_vti.c
+++ b/net/ipv6/ip6_vti.c
@@ -480,10 +480,6 @@ vti6_xmit(struct sk_buff *skb, struct net_device *dev, struct flowi *fl)
 		goto tx_err_dst_release;
 	}
 
-	skb_scrub_packet(skb, !net_eq(t->net, dev_net(dev)));
-	skb_dst_set(skb, dst);
-	skb->dev = skb_dst(skb)->dev;
-
 	mtu = dst_mtu(dst);
 	if (!skb->ignore_df && skb->len > mtu) {
 		skb_dst_update_pmtu(skb, mtu);
@@ -498,9 +494,14 @@ vti6_xmit(struct sk_buff *skb, struct net_device *dev, struct flowi *fl)
 				  htonl(mtu));
 		}
 
-		return -EMSGSIZE;
+		err = -EMSGSIZE;
+		goto tx_err_dst_release;
 	}
 
+	skb_scrub_packet(skb, !net_eq(t->net, dev_net(dev)));
+	skb_dst_set(skb, dst);
+	skb->dev = skb_dst(skb)->dev;
+
 	err = dst_output(t->net, skb->sk, skb);
 	if (net_xmit_eval(err) == 0) {
 		struct pcpu_sw_netstats *tstats = this_cpu_ptr(dev->tstats);
-- 
2.7.4

Re: [PATCH ipsec] vti6: fix PMTU caching and reporting on xmit

[Steffen Klassert]

On Thu, Jun 07, 2018 at 10:11:02AM +0300, Eyal Birger wrote:
> When setting the skb->dst before doing the MTU check, the route PMTU
> caching and reporting is done on the new dst which is about to be
> released.
> 
> Instead, PMTU handling should be done using the original dst.
> 
> This is aligned with IPv4 VTI.
> 
> Signed-off-by: Eyal Birger <eyal.birger@gmail.com>
> Fixes: ccd740cbc6 ("vti6: Add pmtu handling to vti6_xmit.")

Patch applied, thanks for catching this Eyal!