udhcpc: an option to perform ARP check (Jonas Danielsson <jonas.danielsson@axis.com>)

configurable, ~+300 bytes when on.

1 files changed, 20 insertions, 9 deletions

diff --git a/networking/udhcp/arpping.c b/networking/udhcp/arpping.c
index 7b702d8..45597c0 100644
--- a/networking/udhcp/arpping.c
+++ b/networking/udhcp/arpping.c
@@ -32,12 +32,16 @@ struct arpMsg {
 	uint8_t  pad[18];       /* 2a pad for min. ethernet payload (60 bytes) */
 } ATTRIBUTE_PACKED;
 
+enum {
+	ARP_MSG_SIZE = 0x2a
+};
+
 
 /* Returns 1 if no reply received */
 
 int arpping(uint32_t test_ip, uint32_t from_ip, uint8_t *from_mac, const char *interface)
 {
-	int timeout_ms = 2000;
+	int timeout_ms;
 	struct pollfd pfd[1];
 #define s (pfd[0].fd)           /* socket */
 	int rv = 1;             /* "no reply received" yet */
@@ -51,7 +55,7 @@ int arpping(uint32_t test_ip, uint32_t from_ip, uint8_t *from_mac, const char *i
 	}
 
 	if (setsockopt_broadcast(s) == -1) {
-		bb_perror_msg("cannot setsocketopt on raw socket");
+		bb_perror_msg("cannot enable bcast on raw socket");
 		goto ret;
 	}
 
@@ -67,28 +71,35 @@ int arpping(uint32_t test_ip, uint32_t from_ip, uint8_t *from_mac, const char *i
 	arp.operation = htons(ARPOP_REQUEST);           /* ARP op code */
 	memcpy(arp.sHaddr, from_mac, 6);                /* source hardware address */
 	memcpy(arp.sInaddr, &from_ip, sizeof(from_ip)); /* source IP address */
-	/* tHaddr */                                    /* target hardware address */
+	/* tHaddr is zero-fiiled */                     /* target hardware address */
 	memcpy(arp.tInaddr, &test_ip, sizeof(test_ip)); /* target IP address */
 
 	memset(&addr, 0, sizeof(addr));
 	safe_strncpy(addr.sa_data, interface, sizeof(addr.sa_data));
-	if (sendto(s, &arp, sizeof(arp), 0, &addr, sizeof(addr)) < 0)
+	if (sendto(s, &arp, sizeof(arp), 0, &addr, sizeof(addr)) < 0) {
+		// TODO: error message? caller didn't expect us to fail,
+		// just returning 1 "no reply received" misleads it.
 		goto ret;
+	}
 
 	/* wait for arp reply, and check it */
+	timeout_ms = 2000;
 	do {
 		int r;
 		unsigned prevTime = monotonic_us();
 
 		pfd[0].events = POLLIN;
 		r = safe_poll(pfd, 1, timeout_ms);
-		if (r < 0) {
+		if (r < 0)
 			break;
-		} else if (r) {
-			if (read(s, &arp, sizeof(arp)) < 0)
+		if (r) {
+			r = read(s, &arp, sizeof(arp));
+			if (r < 0)
 				break;
-			if (arp.operation == htons(ARPOP_REPLY)
-			 && memcmp(arp.tHaddr, from_mac, 6) == 0
+			if (r >= ARP_MSG_SIZE
+			 && arp.operation == htons(ARPOP_REPLY)
+			 /* don't check it: Linux doesn't return proper tHaddr (fixed in 2.6.24?) */
+			 /* && memcmp(arp.tHaddr, from_mac, 6) == 0 */
 			 && *((uint32_t *) arp.sInaddr) == test_ip
 			) {
 				rv = 0;