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 eae8b908649781c36c19a670e641fc81ad3b12ed..35a020a7098523d80eb956d9ccf5ad1827ae6afb 100644 (file)
--- 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;