have icmp_reflect use route sourceaddr.

this makes it behave like the in_pcb source address selection.

ok claudio@ bluhm@

Author: dlg

sys/netinet/ip_icmp.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: ip_icmp.c,v 1.200 2025/06/12 20:37:59 deraadt Exp $	*/
+/*	$OpenBSD: ip_icmp.c,v 1.201 2025/06/20 05:08:07 dlg Exp $	*/
 /*	$NetBSD: ip_icmp.c,v 1.19 1996/02/13 23:42:22 christos Exp $	*/
 
 /*
@@ -692,7 +692,8 @@ icmp_reflect(struct mbuf *m, struct mbuf **op, struct in_ifaddr *ia)
 	struct ip *ip = mtod(m, struct ip *);
 	struct mbuf *opts = NULL;
 	struct sockaddr_in sin;
-	struct rtentry *rt = NULL;
+	struct rtentry *rt;
+	struct in_addr ip_src = { INADDR_ANY };
 	int optlen = (ip->ip_hl << 2) - sizeof(struct ip);
 	u_int rtableid;
 	u_int8_t pfflags;
@@ -709,10 +710,6 @@ icmp_reflect(struct mbuf *m, struct mbuf **op, struct in_ifaddr *ia)
 		return (ELOOP);
 	}
 	rtableid = m->m_pkthdr.ph_rtableid;
-	pfflags = m->m_pkthdr.pf.flags;
-	m_resethdr(m);
-	m->m_pkthdr.ph_rtableid = rtableid;
-	m->m_pkthdr.pf.flags = pfflags & PF_TAG_GENERATED;
 
 	/*
 	 * If the incoming packet was addressed directly to us,
@@ -726,42 +723,64 @@ icmp_reflect(struct mbuf *m, struct mbuf **op, struct in_ifaddr *ia)
 		sin.sin_addr = ip->ip_dst;
 
 		rt = rtalloc(sintosa(&sin), 0, rtableid);
-		if (rtisvalid(rt) &&
-		    ISSET(rt->rt_flags, RTF_LOCAL|RTF_BROADCAST))
-			ia = ifatoia(rt->rt_ifa);
-	}
+		if (rtisvalid(rt)) {
+			if (ISSET(rt->rt_flags, RTF_LOCAL))
+				ip_src = ip->ip_dst;
+			else if (ISSET(rt->rt_flags, RTF_BROADCAST)) {
+				ia = ifatoia(rt->rt_ifa);
+				ip_src = ia->ia_addr.sin_addr;
+			}
+		}
+		rtfree(rt);
+	} else
+		ip_src = ia->ia_addr.sin_addr;
 
 	/*
 	 * The following happens if the packet was not addressed to us.
-	 * Use the new source address and do a route lookup. If it fails
-	 * drop the packet as there is no path to the host.
+	 * If we're directly connected use the closest address, otherwise
+	 * try to use the sourceaddr from the routing table.
 	 */
-	if (ia == NULL) {
-		rtfree(rt);
-
+	if (ip_src.s_addr == INADDR_ANY) {
 		memset(&sin, 0, sizeof(sin));
 		sin.sin_len = sizeof(sin);
 		sin.sin_family = AF_INET;
 		sin.sin_addr = ip->ip_src;
 
 		/* keep packet in the original virtual instance */
 		rt = rtalloc(sintosa(&sin), RT_RESOLVE, rtableid);
-		if (rt == NULL) {
-			ipstat_inc(ips_noroute);
-			m_freem(m);
-			return (EHOSTUNREACH);
+		if (rtisvalid(rt) &&
+		    ISSET(rt->rt_flags, RTF_LLINFO|RTF_HOST)) {
+			ia = ifatoia(rt->rt_ifa);
+			ip_src = ia->ia_addr.sin_addr;
+		} else {
+			struct sockaddr *sourceaddr;
+			struct ifaddr *ifa;
+
+			sourceaddr = rtable_getsource(rtableid, AF_INET);
+			if (sourceaddr != NULL) {
+				ifa = ifa_ifwithaddr(sourceaddr, rtableid);
+				if (ifa != NULL &&
+				    ISSET(ifa->ifa_ifp->if_flags, IFF_UP))
+					ip_src = satosin(sourceaddr)->sin_addr;
+			}
 		}
-
-		ia = ifatoia(rt->rt_ifa);
+		rtfree(rt);
 	}
 
+	/*
+	 * If the above didn't find an ip_src, ip_output() will try
+	 * and fill it in for us.
+	 */
+
+	pfflags = m->m_pkthdr.pf.flags;
+
+	m_resethdr(m);
+	m->m_pkthdr.ph_rtableid = rtableid;
+	m->m_pkthdr.pf.flags = pfflags & PF_TAG_GENERATED;
 	ip->ip_dst = ip->ip_src;
+	ip->ip_src = ip_src;
 	ip->ip_ttl = MAXTTL;
 
-	/* It is safe to dereference ``ia'' iff ``rt'' is valid. */
-	ip->ip_src = ia->ia_addr.sin_addr;
-	rtfree(rt);
-
 	if (optlen > 0) {
 		u_char *cp;
 		int opt, cnt;