allow /31s on broadcast interfaces (eg ethernet) to work as per rfc3021.

the issue in our kernel was the broadcast address calculated on the /31
caused a ton of checks for use of broadcast addresses to kick in and
prevent one of the two addresses on the /31 from being used.

this diff basically detects if a /31 has been configured and doesnt
configure a broadcast address for it, which makes the ips usable
for normal traffic.

i wrote this so i could interoperate with "carrier" network gear
better, and sthen wants it so he can conserve address space use.

the further special casing of broadcast address handling was from claudio@

ok claudio@ markus@ sthen@ henning@

4 files changed, 27 insertions, 10 deletions

diff --git a/sys/netinet/in.c b/sys/netinet/in.c
index 5ac859edea9..9167486dd95 100644
--- a/sys/netinet/in.c
+++ b/sys/netinet/in.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: in.c,v 1.67 2011/07/03 06:24:13 dlg Exp $	*/
+/*	$OpenBSD: in.c,v 1.68 2011/07/06 01:57:37 dlg Exp $	*/
 /*	$NetBSD: in.c,v 1.26 1996/02/13 23:41:39 christos Exp $	*/
 
 /*
@@ -700,8 +700,12 @@ in_ifinit(struct ifnet *ifp, struct in_ifaddr *ia, struct sockaddr_in *sin,
 	 */
 	ia->ia_ifa.ifa_metric = ifp->if_metric;
 	if (ifp->if_flags & IFF_BROADCAST) {
-		ia->ia_broadaddr.sin_addr.s_addr =
-			ia->ia_net | ~ia->ia_netmask;
+		if (IN_RFC3021_SUBNET(ia->ia_netmask))
+			ia->ia_broadaddr.sin_addr.s_addr = 0;
+		else {
+			ia->ia_broadaddr.sin_addr.s_addr =
+			    ia->ia_net | ~ia->ia_netmask;
+		}
 	} else if (ifp->if_flags & IFF_LOOPBACK) {
 		ia->ia_dstaddr = ia->ia_addr;
 		flags |= RTF_HOST;
diff --git a/sys/netinet/in.h b/sys/netinet/in.h
index 979f61ff831..adfd4b31f6f 100644
--- a/sys/netinet/in.h
+++ b/sys/netinet/in.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: in.h,v 1.89 2011/06/15 09:11:01 mikeb Exp $	*/
+/*	$OpenBSD: in.h,v 1.90 2011/07/06 01:57:37 dlg Exp $	*/
 /*	$NetBSD: in.h,v 1.20 1996/02/13 23:41:47 christos Exp $	*/
 
 /*
@@ -187,6 +187,12 @@ struct in_addr {
 #define	IN_CLASSD_HOST		__IPADDR(0x0fffffff)
 #define	IN_MULTICAST(i)		IN_CLASSD(i)
 
+#define	IN_RFC3021_NET		__IPADDR(0xfffffffe)
+#define	IN_RFC3021_NSHIFT	31
+#define	IN_RFC3021_HOST		__IPADDR(0x00000001)
+#define	IN_RFC3021_SUBNET(n)	(((u_int32_t)(n) & IN_RFC3021_NET) == \
+				 IN_RFC3021_NET)
+
 #define	IN_EXPERIMENTAL(i)	(((u_int32_t)(i) & __IPADDR(0xf0000000)) == \
 				 __IPADDR(0xf0000000))
 #define	IN_BADCLASS(i)		(((u_int32_t)(i) & __IPADDR(0xf0000000)) == \
diff --git a/sys/netinet/in_pcb.c b/sys/netinet/in_pcb.c
index df5c49d2b37..a36b09cbb6c 100644
--- a/sys/netinet/in_pcb.c
+++ b/sys/netinet/in_pcb.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: in_pcb.c,v 1.123 2011/07/05 21:40:38 dhill Exp $	*/
+/*	$OpenBSD: in_pcb.c,v 1.124 2011/07/06 01:57:37 dlg Exp $	*/
 /*	$NetBSD: in_pcb.c,v 1.25 1996/02/13 23:41:53 christos Exp $	*/
 
 /*
@@ -402,8 +402,10 @@ in_pcbconnect(void *v, struct mbuf *nam)
 		if (sin->sin_addr.s_addr == INADDR_ANY)
 			sin->sin_addr = TAILQ_FIRST(&in_ifaddr)->ia_addr.sin_addr;
 		else if (sin->sin_addr.s_addr == INADDR_BROADCAST &&
-		  (TAILQ_FIRST(&in_ifaddr)->ia_ifp->if_flags & IFF_BROADCAST))
-			sin->sin_addr = TAILQ_FIRST(&in_ifaddr)->ia_broadaddr.sin_addr;
+		  (TAILQ_FIRST(&in_ifaddr)->ia_ifp->if_flags & IFF_BROADCAST) &&
+		  TAILQ_FIRST(&in_ifaddr)->ia_broadaddr.sin_addr.s_addr)
+			sin->sin_addr =
+			    TAILQ_FIRST(&in_ifaddr)->ia_broadaddr.sin_addr;
 	}
 	if (inp->inp_laddr.s_addr == INADDR_ANY) {
 		int error;
diff --git a/sys/netinet/ip_icmp.c b/sys/netinet/ip_icmp.c
index b69264495f9..8fdbef04b10 100644
--- a/sys/netinet/ip_icmp.c
+++ b/sys/netinet/ip_icmp.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: ip_icmp.c,v 1.93 2011/04/04 16:33:52 claudio Exp $	*/
+/*	$OpenBSD: ip_icmp.c,v 1.94 2011/07/06 01:57:37 dlg Exp $	*/
 /*	$NetBSD: ip_icmp.c,v 1.19 1996/02/13 23:42:22 christos Exp $	*/
 
 /*
@@ -533,8 +533,12 @@ icmp_input(struct mbuf *m, ...)
 		icp->icmp_type = ICMP_MASKREPLY;
 		icp->icmp_mask = ia->ia_sockmask.sin_addr.s_addr;
 		if (ip->ip_src.s_addr == 0) {
-			if (ia->ia_ifp->if_flags & IFF_BROADCAST)
-				ip->ip_src = ia->ia_broadaddr.sin_addr;
+			if (ia->ia_ifp->if_flags & IFF_BROADCAST) {
+				if (ia->ia_broadaddr.sin_addr.s_addr)
+					ip->ip_src = ia->ia_broadaddr.sin_addr;
+				else
+					ip->ip_src.s_addr = INADDR_BROADCAST;
+			}
 			else if (ia->ia_ifp->if_flags & IFF_POINTOPOINT)
 				ip->ip_src = ia->ia_dstaddr.sin_addr;
 		}
@@ -674,6 +678,7 @@ icmp_reflect(struct mbuf *m, struct mbuf **op, struct in_ifaddr *ia)
 			if (t.s_addr == ia->ia_addr.sin_addr.s_addr)
 				break;
 			if ((ia->ia_ifp->if_flags & IFF_BROADCAST) &&
+			    ia->ia_broadaddr.sin_addr.s_addr != 0 &&
 			    t.s_addr == ia->ia_broadaddr.sin_addr.s_addr)
 				break;
 		}