Switch traceroute over to make use of proper in-kernel source

address selection.

Reviewed by:	rwatson, fenner
MFC after:	1 week
X-MFCable to:	stable/8, stable/7 (after r183571).
PR:		kern/139454
Tested by:	Frank Steinborn (steinex nognu.de)

usr.sbin/traceroute/Makefile

@@ -5,7 +5,7 @@ TRACEROUTE_DISTDIR?= ${.CURDIR}/../../contrib/traceroute
 
 PROG=	traceroute
 MAN=	traceroute.8
-SRCS=	as.c version.c traceroute.c ifaddrlist.c findsaddr-socket.c
+SRCS=	as.c version.c traceroute.c ifaddrlist.c findsaddr-udp.c
 BINOWN=	root
 BINMODE=4555
 CLEANFILES=	version.c
@@ -29,7 +29,7 @@ DPADD=	${LIBIPSEC}
 LDADD=	-lipsec
 .endif
 
-CFLAGS+= -I${TRACEROUTE_DISTDIR}/lbl
+CFLAGS+= -I${TRACEROUTE_DISTDIR}/lbl -I${TRACEROUTE_DISTDIR}
 
 WARNS?=	0
 

usr.sbin/traceroute/findsaddr-udp.c

@@ -0,0 +1,94 @@
+/*-
+ * Copyright (c) 2010 Bjoern A. Zeeb <bz@FreeBSD.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ * $FreeBSD$
+ */
+
+#include <string.h>
+#include <unistd.h>
+
+#include <sys/types.h>
+#include <sys/socket.h>
+
+#include <netinet/in.h>
+
+#include "findsaddr.h"
+#include "traceroute.h"
+
+/*
+ * Return the source address for the given destination address.
+ *
+ * This makes use of proper source address seclection in the FreeBSD kernel
+ * even taking jails into account (sys/netinet/in_pcb.c:in_pcbladdr()).
+ * We open a UDP socket, and connect to the destination, letting the kernel
+ * do the bind and then read the source IPv4 address using getsockname(2).
+ * This has multiple advantages: no need to do PF_ROUTE operations possibly
+ * needing special privileges, jails properly taken into account and most
+ * important - getting the result the kernel would give us rather than
+ * best-guessing ourselves.
+ */
+const char *
+findsaddr(register const struct sockaddr_in *to,
+    register struct sockaddr_in *from)
+{
+	const char *errstr;
+	struct sockaddr_in cto, cfrom;
+	int s;
+	socklen_t len;
+
+	s = socket(AF_INET, SOCK_DGRAM, 0);
+	if (s == -1)
+		return ("failed to open DGRAM socket for src addr selection.");
+
+	errstr = NULL;
+	len = sizeof(struct sockaddr_in);
+	memcpy(&cto, to, len);
+	cto.sin_port = htons(65535);	/* Dummy port for connect(2). */
+	if (connect(s, (struct sockaddr *)&cto, len) == -1) {
+		errstr = "failed to connect to peer for src addr selection.";
+		goto err;
+	}
+
+	if (getsockname(s, (struct sockaddr *)&cfrom, &len) == -1) {
+		errstr = "failed to get socket name for src addr selection.";
+		goto err;
+	}
+
+	if (len != sizeof(struct sockaddr_in) || cfrom.sin_family != AF_INET) {
+		errstr = "unexpected address family in src addr selection.";
+		goto err;
+	}
+
+	/* Update source address for traceroute. */
+	setsin(from, cfrom.sin_addr.s_addr);
+
+err:
+	(void) close(s);
+
+	/* No error (string) to return. */
+	return (errstr);
+}
+
+/* end */