From: Eyal Birger <eyal.birger@gmail.com>
Date: Sat, 20 Feb 2021 13:01:15 +0000 (+0200)
Subject: xfrm: interface: fix ipv4 pmtu check to honor ip header df
X-Git-Tag: v4.19.187~38
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=b318f319b0c81965adaba0997cdddd9e280270d5;p=thirdparty%2Fkernel%2Fstable.git

xfrm: interface: fix ipv4 pmtu check to honor ip header df

[ Upstream commit 8fc0e3b6a8666d656923d214e4dc791e9a17164a ]

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

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

Fixes: f203b76d7809 ("xfrm: Add virtual xfrm interfaces")
Signed-off-by: Eyal Birger <eyal.birger@gmail.com>
Reviewed-by: Sabrina Dubroca <sd@queasysnail.net>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

diff --git a/net/xfrm/xfrm_interface.c b/net/xfrm/xfrm_interface.c
index eae8b90864978..35a020a709852 100644
--- a/net/xfrm/xfrm_interface.c
+++ b/net/xfrm/xfrm_interface.c
@@ -302,6 +302,8 @@ xfrmi_xmit2(struct sk_buff *skb, struct net_device *dev, struct flowi *fl)
 
 			icmpv6_ndo_send(skb, ICMPV6_PKT_TOOBIG, 0, mtu);
 		} else {
+			if (!(ip_hdr(skb)->frag_off & htons(IP_DF)))
+				goto xmit;
 			icmp_ndo_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED,
 				      htonl(mtu));
 		}
@@ -310,6 +312,7 @@ xfrmi_xmit2(struct sk_buff *skb, struct net_device *dev, struct flowi *fl)
 		return -EMSGSIZE;
 	}
 
+xmit:
 	xfrmi_scrub_packet(skb, !net_eq(xi->net, dev_net(dev)));
 	skb_dst_set(skb, dst);
 	skb->dev = tdev;