Patch by Stefan Tomanek <stefan@pico.ruhr.de> for dsniff >= 2.4b1 to allow the
selection of source hw address.

In certain networks, sending with the wrong hardware source address can jeopardize
the network connection of the host running arpspoof. This patch makes it possible
to specify whether arpspoof should use the own hardware address or the one of the
real host when resetting the arp table of the target systems; it is also possible
to use both.

For some more information, please have a look to Debian bug ID #650752.

--- dsniff-2.4/arpspoof.8			2013-12-20 20:54:25.000000000 +0100
+++ dsniff-2.4/arpspoof.8.arpspoof_hwaddr	2013-12-20 20:55:19.000000000 +0100
@@ -9,7 +9,7 @@
 .na
 .nf
 .fi
-\fBarpspoof\fR [\fB\-i \fIinterface\fR] [\fB\-t \fItarget\fR] [\fB\-r\fR] \fIhost\fR
+\fBarpspoof\fR [\fB\-i \fIinterface\fR] [\fB\-c \fIown|host|both\fR] [\fB\-t \fItarget\fR] [\fB\-r\fR] \fIhost\fR
 .SH DESCRIPTION
 .ad
 .fi
@@ -23,6 +23,13 @@
 .SH OPTIONS
 .IP "\fB-i \fIinterface\fR"
 Specify the interface to use.
+.IP "\fB-c \fIown|host|both\fR"
+Specify which hardware address t use when restoring the arp configuration;
+while cleaning up, packets can be send with the own address as well as with
+the address of the host. Sending packets with a fake hw address can disrupt
+connectivity with certain switch/ap/bridge configurations, however it works
+more reliably than using the own address, which is the default way arpspoof
+cleans up afterwards.
 .IP "\fB-t \fItarget\fR"
 Specify a particular host to ARP poison (if not specified, all hosts
 on the LAN).  Repeat to specify multiple hosts.
--- dsniff-2.4/arpspoof.c			2013-12-20 20:54:25.000000000 +0100
+++ dsniff-2.4/arpspoof.c.arpspoof_hwaddr	2013-12-20 21:02:10.000000000 +0100
@@ -40,37 +40,36 @@
 static char *intf;
 static int poison_reverse;
 
+static uint8_t *my_ha = NULL;
+static uint8_t *brd_ha = "\xff\xff\xff\xff\xff\xff";
+
+static int cleanup_src_own = 1;
+static int cleanup_src_host = 0;
+
 static void
 usage(void)
 {
 	fprintf(stderr, "Version: " VERSION "\n"
-		"Usage: arpspoof [-i interface] [-t target] [-r] host\n");
+		"Usage: arpspoof [-i interface] [-c own|host|both] [-t target] [-r] host\n");
 	exit(1);
 }
 
 static int
-arp_send(libnet_t *l, int op, u_int8_t *sha,
-	 in_addr_t spa, u_int8_t *tha, in_addr_t tpa)
+arp_send(libnet_t *l, int op,
+	 u_int8_t *sha, in_addr_t spa,
+	 u_int8_t *tha, in_addr_t tpa,
+	 u_int8_t *me)
 {
 	int retval;
 
-	if (sha == NULL &&
-	    (sha = (u_int8_t *)libnet_get_hwaddr(l)) == NULL) {
-		return (-1);
-	}
-	if (spa == 0) {
-		if ((spa = libnet_get_ipaddr4(l)) == -1)
-			return (-1);
-	}
-	if (tha == NULL)
-		tha = "\xff\xff\xff\xff\xff\xff";
+	if (!me) me = sha;
 	
 	libnet_autobuild_arp(op, sha, (u_int8_t *)&spa,
 			     tha, (u_int8_t *)&tpa, l);
-	libnet_build_ethernet(tha, sha, ETHERTYPE_ARP, NULL, 0, l, 0);
+	libnet_build_ethernet(tha, me, ETHERTYPE_ARP, NULL, 0, l, 0);
 	
 	fprintf(stderr, "%s ",
-		ether_ntoa((struct ether_addr *)sha));
+		ether_ntoa((struct ether_addr *)me));
 
 	if (op == ARPOP_REQUEST) {
 		fprintf(stderr, "%s 0806 42: arp who-has %s tell %s\n",
@@ -129,7 +128,7 @@
 		/* XXX - force the kernel to arp. feh. */
 		arp_force(ip);
 #else
-		arp_send(l, ARPOP_REQUEST, NULL, 0, NULL, ip);
+		arp_send(l, ARPOP_REQUEST, NULL, 0, NULL, ip, NULL);
 #endif
 		sleep(1);
 	}
@@ -156,17 +155,22 @@
 	int fw = arp_find(spoof.ip, &spoof.mac);
 	int bw = poison_reverse && targets[0].ip && arp_find_all();
 	int i;
+	int rounds = (cleanup_src_own*5 + cleanup_src_host*5);
 	
 	fprintf(stderr, "Cleaning up and re-arping targets...\n");
-	for (i = 0; i < 5; i++) {
+	for (i = 0; i < rounds; i++) {
 		struct host *target = targets;
 		while(target->ip) {
+			uint8_t *src_ha = NULL;
+			if (cleanup_src_own && (i%2 || !cleanup_src_host)) {
+				src_ha = my_ha;
+			}
 			/* XXX - on BSD, requires ETHERSPOOF kernel. */
 			if (fw) {
 				arp_send(l, ARPOP_REPLY,
 					 (u_int8_t *)&spoof.mac, spoof.ip,
-					 (target->ip ? (u_int8_t *)&target->mac : NULL),
-					 target->ip);
+					 (target->ip ? (u_int8_t *)&target->mac : brd_ha),
+					 target->ip, src_ha);
 				/* we have to wait a moment before sending the next packet */
 				sleep(1);
 			}
@@ -174,7 +178,7 @@
 				arp_send(l, ARPOP_REPLY,
 					 (u_int8_t *)&target->mac, target->ip,
 					 (u_int8_t *)&spoof.mac,
-					 spoof.ip);
+					 spoof.ip, src_ha);
 				sleep(1);
 			}
 			target++;
@@ -193,6 +197,7 @@
 	char libnet_ebuf[LIBNET_ERRBUF_SIZE];
 	int c;
 	int n_targets;
+	char *cleanup_src = NULL;
 	
 	spoof.ip = 0;
 	intf = NULL;
@@ -202,7 +207,7 @@
 	/* allocate enough memory for target list */
 	targets = calloc( argc+1, sizeof(struct host) );
 	
-	while ((c = getopt(argc, argv, "ri:t:h?V")) != -1) {
+	while ((c = getopt(argc, argv, "ri:t:c:h?V")) != -1) {
 		switch (c) {
 		case 'i':
 			intf = optarg;
@@ -214,6 +219,9 @@
 		case 'r':
 			poison_reverse = 1;
 			break;
+		case 'c':
+			cleanup_src = optarg;
+			break;
 		default:
 			usage();
 		}
@@ -229,6 +237,29 @@
 		usage();
 	}
 	
+	if (!cleanup_src || strcmp(cleanup_src, "own") == 0) { /* default! */
+		/* only use our own hw address when cleaning up,
+		 * not jeopardizing any bridges on the way to our
+		 * target
+		 */
+		cleanup_src_own = 1;
+		cleanup_src_host = 0;
+	} else if (strcmp(cleanup_src, "host") == 0) {
+		/* only use the target hw address when cleaning up;
+		 * this can screw up some bridges and scramble access
+		 * for our own host, however it resets the arp table
+		 * more reliably
+		 */
+		cleanup_src_own = 0;
+		cleanup_src_host = 1;
+	} else if (strcmp(cleanup_src, "both") == 0) {
+		cleanup_src_own = 1;
+		cleanup_src_host = 1;
+	} else {
+		errx(1, "Invalid parameter to -c: use 'own' (default), 'host' or 'both'.");
+		usage();
+	}
+	
 	if ((spoof.ip = libnet_name2addr4(l, argv[0], LIBNET_RESOLVE)) == -1)
 		usage();
 	
@@ -253,6 +284,10 @@
 		}
 	}
 	
+	if ((my_ha = (u_int8_t *)libnet_get_hwaddr(l)) == NULL) {
+		errx(1, "Unable to determine own mac address");
+	}
+	
 	signal(SIGHUP, cleanup);
 	signal(SIGINT, cleanup);
 	signal(SIGTERM, cleanup);
@@ -260,11 +295,11 @@
 	for (;;) {
 		struct host *target = targets;
 		while(target->ip) {
-			arp_send(l, ARPOP_REPLY, NULL, spoof.ip,
-				 (target->ip ? (u_int8_t *)&target->mac : NULL),
-				 target->ip);
+			arp_send(l, ARPOP_REPLY, my_ha, spoof.ip,
+				 (target->ip ? (u_int8_t *)&target->mac : brd_ha),
+				 target->ip, my_ha);
 			if (poison_reverse) {
-				arp_send(l, ARPOP_REPLY, NULL, target->ip, (uint8_t *)&spoof.mac, spoof.ip);
+				arp_send(l, ARPOP_REPLY, my_ha, target->ip, (uint8_t *)&spoof.mac, spoof.ip, my_ha);
 			}
 			target++;
 		}
