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

BugLink: https://bugs.launchpad.net/bugs/1926368
[ 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>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/net/xfrm/xfrm_interface.c b/net/xfrm/xfrm_interface.c
index 697cdcfbb5e1afdcd6290f466d95a882f1848da4..3f42c2f15ba4547353a733a08b60a772532dc112 100644 (file)
--- a/net/xfrm/xfrm_interface.c
+++ b/net/xfrm/xfrm_interface.c
@@ -305,6 +305,8 @@ 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));
                }
@@ -313,6 +315,7 @@ 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;