fix up mtu for routes and ongoing tcp connection when if mtu changes

from FreeBSD; fixes pr/1878

2 files changed, 24 insertions, 2 deletions

diff --git a/sys/netinet/ip_output.c b/sys/netinet/ip_output.c
index c6ca2c6e493..dfd4cc19d63 100644
--- a/sys/netinet/ip_output.c
+++ b/sys/netinet/ip_output.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: ip_output.c,v 1.105 2001/06/23 02:27:10 angelos Exp $	*/
+/*	$OpenBSD: ip_output.c,v 1.106 2001/06/23 03:10:21 provos Exp $	*/
 /*	$NetBSD: ip_output.c,v 1.28 1996/02/13 23:43:07 christos Exp $	*/
 
 /*
@@ -621,6 +621,18 @@ sendit:
 	 */
 	if (ip->ip_off & IP_DF) {
 		error = EMSGSIZE;
+		/*
+		 * This case can happen if the user changed the MTU
+		 * of an interface after enabling IP on it.  Because
+		 * most netifs don't keep track of routes pointing to
+		 * them, there is no way for one to update all its
+		 * routes when the MTU is changed.
+		 */
+		if ((ro->ro_rt->rt_flags & (RTF_UP | RTF_HOST))
+		    && !(ro->ro_rt->rt_rmx.rmx_locks & RTV_MTU)
+		    && (ro->ro_rt->rt_rmx.rmx_mtu > ifp->if_mtu)) {
+			ro->ro_rt->rt_rmx.rmx_mtu = ifp->if_mtu;
+		}
 		ipstat.ips_cantfrag++;
 		goto bad;
 	}
diff --git a/sys/netinet/tcp_output.c b/sys/netinet/tcp_output.c
index a694cc0886d..37c2419b1ca 100644
--- a/sys/netinet/tcp_output.c
+++ b/sys/netinet/tcp_output.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: tcp_output.c,v 1.37 2001/06/08 03:53:46 angelos Exp $	*/
+/*	$OpenBSD: tcp_output.c,v 1.38 2001/06/23 03:10:21 provos Exp $	*/
 /*	$NetBSD: tcp_output.c,v 1.16 1997/06/03 16:17:09 kml Exp $	*/
 
 /*
@@ -1102,6 +1102,16 @@ out:
 			tcp_quench(tp->t_inpcb, 0);
 			return (0);
 		}
+		if (error == EMSGSIZE) {
+			/*
+			 * ip_output() will have already fixed the route
+			 * for us.  tcp_mtudisc() will, as its last action,
+			 * initiate retransmission, so it is important to
+			 * not do so here.
+			 */
+			tcp_mtudisc(tp->t_inpcb, 0);
+			return (0);
+		}
 		if ((error == EHOSTUNREACH || error == ENETDOWN)
 		    && TCPS_HAVERCVDSYN(tp->t_state)) {
 			tp->t_softerror = error;