Ensure that the syn cache's syn-ack packets contain the same

ip_tos, ip_ttl, and DF bits as all other tcp packets.

PR:		39141
MFC after:	2 weeks

1 files changed, 18 insertions, 0 deletions

diff --git a/sys/netinet/tcp_syncache.c b/sys/netinet/tcp_syncache.c
index 40defbe..e4c467e 100644
--- a/sys/netinet/tcp_syncache.c
+++ b/sys/netinet/tcp_syncache.c
@@ -1128,6 +1128,24 @@ syncache_respond(sc, m)
 
 		th = (struct tcphdr *)(ip + 1);
 	}
+
+	ip->ip_ttl = sc->sc_tp->t_inpcb->inp_ip_ttl;   /* XXX */
+	ip->ip_tos = sc->sc_tp->t_inpcb->inp_ip_tos;   /* XXX */
+
+	/*
+	 * See if we should do MTU discovery.  We do it only if the following
+	 * are true:
+	 *      1) we have a valid route to the destination
+	 *      2) the MTU is not locked (if it is, then discovery has been  
+	 *         disabled)
+	 */
+	if (path_mtu_discovery
+	    && (rt != NULL)
+	    && rt->rt_flags & RTF_UP
+	    && !(rt->rt_rmx.rmx_locks & RTV_MTU)) {
+	       ip->ip_off |= IP_DF;
+	}
+
 	th->th_sport = sc->sc_inc.inc_lport;
 	th->th_dport = sc->sc_inc.inc_fport;