[PATCH ipsec] xfrm: interface: fix ipv4 pmtu check to honor ip header df

[Eyal Birger]

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.bir...@gmail.com>
---
 net/xfrm/xfrm_interface.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/net/xfrm/xfrm_interface.c b/net/xfrm/xfrm_interface.c
index 697cdcfbb5e1..257b3c8b3995 100644
--- a/net/xfrm/xfrm_interface.c
+++ b/net/xfrm/xfrm_interface.c
@@ -304,13 +304,16 @@ xfrmi_xmit2(struct sk_buff *skb, struct net_device *dev, 
struct flowi *fl)
                                mtu = IPV6_MIN_MTU;
 
                        icmpv6_ndo_send(skb, ICMPV6_PKT_TOOBIG, 0, mtu);
-               } else {
+                       err = -EMSGSIZE;
+                       goto tx_err_dst_release;
+               }
+
+               if (ip_hdr(skb)->frag_off & htons(IP_DF)) {
                        icmp_ndo_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED,
                                      htonl(mtu));
+                       err = -EMSGSIZE;
+                       goto tx_err_dst_release;
                }
-
-               dst_release(dst);
-               return -EMSGSIZE;
        }
 
        xfrmi_scrub_packet(skb, !net_eq(xi->net, dev_net(dev)));
-- 
2.25.1