[src/trunk]: src/sys/netinet6 inet6: Ensure that route MTU is guarded by ARC_...

[roy <roy%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/1357e3e7cba0
branches:  trunk
changeset: 931653:1357e3e7cba0
user:      roy <roy%NetBSD.org@localhost>
date:      Tue Apr 28 15:12:28 2020 +0000

description:
inet6: Ensure that route MTU is guarded by ARC_PHDS_MAXMTU

This mirrors the ARP behavior for ARCnet interfaces based on current
kernel RA handling.

diffstat:

 sys/netinet6/nd6.c |  20 +++++++++++++++++---
 1 files changed, 17 insertions(+), 3 deletions(-)

diffs (42 lines):

diff -r d15d91878ccf -r 1357e3e7cba0 sys/netinet6/nd6.c
--- a/sys/netinet6/nd6.c        Tue Apr 28 14:45:23 2020 +0000
+++ b/sys/netinet6/nd6.c        Tue Apr 28 15:12:28 2020 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: nd6.c,v 1.269 2020/04/12 12:13:52 roy Exp $    */
+/*     $NetBSD: nd6.c,v 1.270 2020/04/28 15:12:28 roy Exp $    */
 /*     $KAME: nd6.c,v 1.279 2002/06/08 11:16:51 itojun Exp $   */
 
 /*
@@ -31,7 +31,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: nd6.c,v 1.269 2020/04/12 12:13:52 roy Exp $");
+__KERNEL_RCSID(0, "$NetBSD: nd6.c,v 1.270 2020/04/28 15:12:28 roy Exp $");
 
 #ifdef _KERNEL_OPT
 #include "opt_net_mpsafe.h"
@@ -1462,8 +1462,22 @@
                return;
        }
 
-       if ((rt->rt_flags & RTF_GATEWAY) != 0)
+       if ((rt->rt_flags & RTF_GATEWAY) != 0) {
+               if (req != RTM_ADD)
+                       return;
+               /*
+                * linklayers with particular MTU limitation.
+                */
+               switch(ifp->if_type) {
+#if NARCNET > 0
+               case IFT_ARCNET:
+                       if (rt->rt_rmx.rmx_mtu > ARC_PHDS_MAXMTU) /* RFC2497 */
+                               rt->rt_rmx.rmx_mtu = ARC_PHDS_MAXMTU;
+                       break;
+#endif
+               }
                return;
+       }
 
        if (nd6_need_cache(ifp) == 0 && (rt->rt_flags & RTF_HOST) == 0) {
                RT_DPRINTF("rt_getkey(rt) = %p\n", rt_getkey(rt));