netdev - [PATCH ipsec 2/2] vti6: fix ipv4 pmtu check to honor ip header df

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Message-Id: <20210226213506.506799-3-eyal.birger@gmail.com>
Date:   Fri, 26 Feb 2021 23:35:06 +0200
From:   Eyal Birger <eyal.birger@...il.com>
To:     steffen.klassert@...unet.com, herbert@...dor.apana.org.au,
        davem@...emloft.net, kuba@...nel.org
Cc:     netdev@...r.kernel.org, bram-yvahk@...l.wizbit.be,
        sd@...asysnail.net, Eyal Birger <eyal.birger@...il.com>
Subject: [PATCH ipsec 2/2] vti6: fix ipv4 pmtu check to honor ip header df

Frag needed should only be sent if the header enables DF.

This fix allows IPv4 packets larger than MTU to pass the vti6 interface
and be fragmented after encapsulation, aligning behavior with
non-vti6 xfrm.

Fixes: ccd740cbc6e0 ("vti6: Add pmtu handling to vti6_xmit.")
Signed-off-by: Eyal Birger <eyal.birger@...il.com>
---
 net/ipv6/ip6_vti.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/ipv6/ip6_vti.c b/net/ipv6/ip6_vti.c
index 0225fd694192..2f0be5ac021c 100644
--- a/net/ipv6/ip6_vti.c
+++ b/net/ipv6/ip6_vti.c
@@ -494,7 +494,7 @@ vti6_xmit(struct sk_buff *skb, struct net_device *dev, struct flowi *fl)
 	}
 
 	if (dst->flags & DST_XFRM_QUEUE)
-		goto queued;
+		goto xmit;
 
 	x = dst->xfrm;
 	if (!vti6_state_check(x, &t->parms.raddr, &t->parms.laddr))
@@ -523,6 +523,8 @@ vti6_xmit(struct sk_buff *skb, struct net_device *dev, struct flowi *fl)
 
 			icmpv6_send(skb, ICMPV6_PKT_TOOBIG, 0, mtu);
 		} else {
+			if (!(ip_hdr(skb)->frag_off & htons(IP_DF)))
+				goto xmit;
 			icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED,
 				  htonl(mtu));
 		}
@@ -531,7 +533,7 @@ vti6_xmit(struct sk_buff *skb, struct net_device *dev, struct flowi *fl)
 		goto tx_err_dst_release;
 	}
 
-queued:
+xmit:
 	skb_scrub_packet(skb, !net_eq(t->net, dev_net(dev)));
 	skb_dst_set(skb, dst);
 	skb->dev = skb_dst(skb)->dev;
-- 
2.25.1