Blob Blame Raw
--- arpwatch-2.1a15-dist/arpwatch.c	2012-07-23 09:55:35.832458313 +0200
+++ arpwatch-2.1a15-new/arpwatch.c	2012-07-24 11:36:59.013953071 +0200
@@ -161,15 +161,63 @@ void dropprivileges(const char* user)
 	syslog(LOG_DEBUG, "Running as uid=%d gid=%d", getuid(), getgid());
 }
 
+char *
+get_first_dev(pcap_t **pd, int *linktype, char *errbuf)
+{
+	static char interface[IF_NAMESIZE + 1];
+	register int snaplen, timeout;
+	pcap_if_t *alldevs;
+	pcap_if_t *dev;
+	char *ret = NULL;
+
+	snaplen = max(sizeof(struct ether_header),
+				  sizeof(struct fddi_header)) + sizeof(struct ether_arp);
+	timeout = 1000;
+
+	if (pcap_findalldevs(&alldevs, errbuf) == -1) {
+		(void)fprintf(stderr, "%s: lookup_device: %s\n",
+					  prog, errbuf);
+		exit(1);
+	}
+
+	for (dev = alldevs; dev; dev = dev->next) {
+		strncpy(interface, dev->name, strlen(dev->name)+1);
+
+		*pd = pcap_open_live(interface, snaplen, 1, timeout, errbuf);
+		if (*pd == NULL) {
+			syslog(LOG_ERR, "pcap open %s: %s, trying next...", interface, errbuf);
+			continue;
+			/* exit(1); */
+		}
+
+		*linktype = pcap_datalink(*pd);
+		/* Must be ethernet or fddi */
+		if (*linktype != DLT_EN10MB && *linktype != DLT_FDDI) {
+			syslog(LOG_ERR, "(%s) Link layer type %d not ethernet or fddi, trying next...",
+				   interface, *linktype);
+			pcap_close(*pd);
+		}
+		else {
+			/* First match, use it */
+			ret = interface;
+			break;
+		}
+
+	}
+	pcap_freealldevs(alldevs);
+	return (ret);
+}
+
 int
 main(int argc, char **argv)
 {
 	register char *cp;
-	register int op, pid, snaplen, timeout, linktype, status;
+	register int op, pid, status;
+	int linktype;
 #ifdef TIOCNOTTY
 	register int fd;
 #endif
-	register pcap_t *pd;
+	pcap_t *pd;
 	register char *interface, *rfilename;
 	struct bpf_program code;
 	char errbuf[PCAP_ERRBUF_SIZE];
@@ -189,6 +237,7 @@ main(int argc, char **argv)
 
 	opterr = 0;
 	interface = NULL;
+	linktype = -1;
 	rfilename = NULL;
 	pd = NULL;
 	while ((op = getopt(argc, argv, "df:i:n:Nr:u:e:s:")) != EOF)
@@ -264,11 +313,12 @@ main(int argc, char **argv)
 		net = 0;
 		netmask = 0;
 	} else {
+
 		/* Determine interface if not specified */
 		if (interface == NULL &&
-		    (interface = pcap_lookupdev(errbuf)) == NULL) {
-			(void)fprintf(stderr, "%s: lookup_device: %s\n",
-			    prog, errbuf);
+			(interface = get_first_dev(&pd, &linktype, errbuf)) == NULL) {
+			(void)fprintf(stderr, "%s: lookup_device: no suitable interface found\n",
+						  prog);
 			exit(1);
 		}
 
@@ -317,10 +367,6 @@ main(int argc, char **argv)
 		}
 		swapped = pcap_is_swapped(pd);
 	} else {
-		snaplen = max(sizeof(struct ether_header),
-		    sizeof(struct fddi_header)) + sizeof(struct ether_arp);
-		timeout = 1000;
-		pd = pcap_open_live(interface, snaplen, 1, timeout, errbuf);
 		if (pd == NULL) {
 			syslog(LOG_ERR, "pcap open %s: %s", interface, errbuf);
 			exit(1);
@@ -340,14 +386,6 @@ main(int argc, char **argv)
 		dropprivileges( serveruser );
 	}
 
-	/* Must be ethernet or fddi */
-	linktype = pcap_datalink(pd);
-	if (linktype != DLT_EN10MB && linktype != DLT_FDDI) {
-		syslog(LOG_ERR, "Link layer type %d not ethernet or fddi",
-		    linktype);
-		exit(1);
-	}
-
 	/* Compile and install filter */
 	if (pcap_compile(pd, &code, "arp or rarp", 1, netmask) < 0) {
 		syslog(LOG_ERR, "pcap_compile: %s", pcap_geterr(pd));