udhcpd: don't fail ARP check if returned MAC matches client's one

Also, do not unicast replies to yiaddr.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

6 files changed, 66 insertions, 33 deletions

diff --git a/networking/udhcp/arpping.c b/networking/udhcp/arpping.c
index b10bff651..fa0989d0f 100644
--- a/networking/udhcp/arpping.c
+++ b/networking/udhcp/arpping.c
@@ -41,7 +41,11 @@ enum {
 
 /* Returns 1 if no reply received */
 
-int FAST_FUNC arpping(uint32_t test_ip, uint32_t from_ip, uint8_t *from_mac, const char *interface)
+int FAST_FUNC arpping(uint32_t test_ip,
+		const uint8_t *safe_mac,
+		uint32_t from_ip,
+		uint8_t *from_mac,
+		const char *interface)
 {
 	int timeout_ms;
 	struct pollfd pfd[1];
@@ -73,7 +77,7 @@ int FAST_FUNC arpping(uint32_t test_ip, uint32_t from_ip, uint8_t *from_mac, con
 	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 is zero-fiiled */                     /* target hardware address */
+	/* tHaddr is zero-filled */                     /* target hardware address */
 	memcpy(arp.tInaddr, &test_ip, sizeof(test_ip)); /* target IP address */
 
 	memset(&addr, 0, sizeof(addr));
@@ -98,13 +102,24 @@ int FAST_FUNC arpping(uint32_t test_ip, uint32_t from_ip, uint8_t *from_mac, con
 			r = read(s, &arp, sizeof(arp));
 			if (r < 0)
 				break;
+
+			//bb_error_msg("sHaddr %02x:%02x:%02x:%02x:%02x:%02x",
+			//	arp.sHaddr[0], arp.sHaddr[1], arp.sHaddr[2],
+			//	arp.sHaddr[3], arp.sHaddr[4], arp.sHaddr[5]);
+
 			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;
+				 /* if ARP source MAC matches safe_mac
+				  * (which is client's MAC), then it's not a conflict
+				  * (client simply already has this IP and replies to ARPs!)
+				  */
+				if (!safe_mac || memcmp(safe_mac, arp.sHaddr, 6) != 0)
+					rv = 0;
+				//else bb_error_msg("sHaddr == safe_mac");
 				break;
 			}
 		}
diff --git a/networking/udhcp/common.h b/networking/udhcp/common.h
index 5a258c064..ca96847a7 100644
--- a/networking/udhcp/common.h
+++ b/networking/udhcp/common.h
@@ -92,7 +92,11 @@ int udhcp_read_interface(const char *interface, int *ifindex, uint32_t *addr, ui
 int udhcp_raw_socket(int ifindex) FAST_FUNC;
 int udhcp_listen_socket(/*uint32_t ip,*/ int port, const char *inf) FAST_FUNC;
 /* Returns 1 if no reply received */
-int arpping(uint32_t test_ip, uint32_t from_ip, uint8_t *from_mac, const char *interface) FAST_FUNC;
+int arpping(uint32_t test_ip,
+		const uint8_t *safe_mac,
+		uint32_t from_ip,
+		uint8_t *from_mac,
+		const char *interface) FAST_FUNC;
 
 #if ENABLE_UDHCP_DEBUG
 # define DEBUG(str, args...) bb_info_msg("### " str, ## args)
diff --git a/networking/udhcp/dhcpc.c b/networking/udhcp/dhcpc.c
index 2dd3cd077..ab34b0472 100644
--- a/networking/udhcp/dhcpc.c
+++ b/networking/udhcp/dhcpc.c
@@ -553,9 +553,10 @@ int udhcpc_main(int argc UNUSED_PARAM, char **argv)
  * the client MUST send a DHCPDECLINE message to the server and restarts
  * the configuration process..." */
 						if (!arpping(packet.yiaddr,
-							    (uint32_t) 0,
-							    client_config.arp,
-							    client_config.interface)
+								NULL,
+								(uint32_t) 0,
+								client_config.arp,
+								client_config.interface)
 						) {
 							bb_info_msg("offered address is in use "
 								"(got ARP reply), declining");
diff --git a/networking/udhcp/dhcpd.h b/networking/udhcp/dhcpd.h
index 9667c61e8..4b5fcc00f 100644
--- a/networking/udhcp/dhcpd.h
+++ b/networking/udhcp/dhcpd.h
@@ -99,7 +99,7 @@ struct dhcpOfferedAddr *add_lease(
 int lease_expired(struct dhcpOfferedAddr *lease) FAST_FUNC;
 struct dhcpOfferedAddr *find_lease_by_chaddr(const uint8_t *chaddr) FAST_FUNC;
 struct dhcpOfferedAddr *find_lease_by_yiaddr(uint32_t yiaddr) FAST_FUNC;
-uint32_t find_free_or_expired_address(void) FAST_FUNC;
+uint32_t find_free_or_expired_address(const uint8_t *chaddr) FAST_FUNC;
 
 
 /*** static_leases.h ***/
diff --git a/networking/udhcp/leases.c b/networking/udhcp/leases.c
index e17fb9e3f..b2cdd1942 100644
--- a/networking/udhcp/leases.c
+++ b/networking/udhcp/leases.c
@@ -118,7 +118,7 @@ struct dhcpOfferedAddr* FAST_FUNC find_lease_by_yiaddr(uint32_t yiaddr)
 
 
 /* check is an IP is taken, if it is, add it to the lease table */
-static int nobody_responds_to_arp(uint32_t addr)
+static int nobody_responds_to_arp(uint32_t addr, const uint8_t *safe_mac)
 {
 	/* 16 zero bytes */
 	static const uint8_t blank_chaddr[16] = { 0 };
@@ -127,7 +127,9 @@ static int nobody_responds_to_arp(uint32_t addr)
 	struct in_addr temp;
 	int r;
 
-	r = arpping(addr, server_config.server, server_config.arp, server_config.interface);
+	r = arpping(addr, safe_mac,
+			server_config.server, server_config.arp,
+			server_config.interface);
 	if (r)
 		return r;
 
@@ -140,7 +142,7 @@ static int nobody_responds_to_arp(uint32_t addr)
 
 
 /* Find a new usable (we think) address. */
-uint32_t FAST_FUNC find_free_or_expired_address(void)
+uint32_t FAST_FUNC find_free_or_expired_address(const uint8_t *chaddr)
 {
 	uint32_t addr;
 	struct dhcpOfferedAddr *oldest_lease = NULL;
@@ -163,7 +165,7 @@ uint32_t FAST_FUNC find_free_or_expired_address(void)
 
 		lease = find_lease_by_yiaddr(net_addr);
 		if (!lease) {
-			if (nobody_responds_to_arp(net_addr))
+			if (nobody_responds_to_arp(net_addr, chaddr))
 				return net_addr;
 		} else {
 			if (!oldest_lease || lease->expires < oldest_lease->expires)
@@ -172,7 +174,7 @@ uint32_t FAST_FUNC find_free_or_expired_address(void)
 	}
 
 	if (oldest_lease && lease_expired(oldest_lease)
-	 && nobody_responds_to_arp(oldest_lease->yiaddr)
+	 && nobody_responds_to_arp(oldest_lease->yiaddr, chaddr)
 	) {
 		return oldest_lease->yiaddr;
 	}
diff --git a/networking/udhcp/serverpacket.c b/networking/udhcp/serverpacket.c
index 8b0f1856b..157d157ba 100644
--- a/networking/udhcp/serverpacket.c
+++ b/networking/udhcp/serverpacket.c
@@ -31,7 +31,8 @@ static int send_packet_to_relay(struct dhcpMessage *payload)
 {
 	DEBUG("Forwarding packet to relay");
 
-	return udhcp_send_kernel_packet(payload, server_config.server, SERVER_PORT,
+	return udhcp_send_kernel_packet(payload,
+			server_config.server, SERVER_PORT,
 			payload->giaddr, SERVER_PORT);
 }
 
@@ -42,23 +43,31 @@ static int send_packet_to_client(struct dhcpMessage *payload, int force_broadcas
 	const uint8_t *chaddr;
 	uint32_t ciaddr;
 
-	if (force_broadcast) {
-		DEBUG("broadcasting packet to client (NAK)");
+	// Was:
+	//if (force_broadcast) { /* broadcast */ }
+	//else if (payload->ciaddr) { /* unicast to payload->ciaddr */ }
+	//else if (payload->flags & htons(BROADCAST_FLAG)) { /* broadcast */ }
+	//else { /* unicast to payload->yiaddr */ }
+	// But this is wrong: yiaddr is _our_ idea what client's IP is
+	// (for example, from lease file). Client may not know that,
+	// and may not have UDP socket listening on that IP!
+	// We should never unicast to payload->yiaddr!
+	// payload->ciaddr, OTOH, comes from client's request packet,
+	// and can be used.
+
+	if (force_broadcast
+	 || (payload->flags & htons(BROADCAST_FLAG))
+	 || !payload->ciaddr
+	) {
+		DEBUG("broadcasting packet to client");
 		ciaddr = INADDR_BROADCAST;
 		chaddr = MAC_BCAST_ADDR;
-	} else if (payload->ciaddr) {
+	} else {
 		DEBUG("unicasting packet to client ciaddr");
 		ciaddr = payload->ciaddr;
 		chaddr = payload->chaddr;
-	} else if (payload->flags & htons(BROADCAST_FLAG)) {
-		DEBUG("broadcasting packet to client (requested)");
-		ciaddr = INADDR_BROADCAST;
-		chaddr = MAC_BCAST_ADDR;
-	} else {
-		DEBUG("unicasting packet to client yiaddr");
-		ciaddr = payload->yiaddr;
-		chaddr = payload->chaddr;
 	}
+
 	return udhcp_send_raw_packet(payload,
 		/*src*/ server_config.server, SERVER_PORT,
 		/*dst*/ ciaddr, CLIENT_PORT, chaddr,
@@ -118,17 +127,18 @@ int FAST_FUNC send_offer(struct dhcpMessage *oldpacket)
 		struct dhcpOfferedAddr *lease;
 
 		lease = find_lease_by_chaddr(oldpacket->chaddr);
-		/* the client is in our lease/offered table */
+		/* The client is in our lease/offered table */
 		if (lease) {
 			signed_leasetime_t tmp = lease->expires - time(NULL);
 			if (tmp >= 0)
 				lease_time_aligned = tmp;
 			packet.yiaddr = lease->yiaddr;
-		/* Or the client has requested an ip */
-		} else if ((req = get_option(oldpacket, DHCP_REQUESTED_IP)) != NULL
-		 /* Don't look here (ugly hackish thing to do) */
+		}
+		/* Or the client has requested an IP */
+		else if ((req = get_option(oldpacket, DHCP_REQUESTED_IP)) != NULL
+		 /* (read IP) */
 		 && (move_from_unaligned32(req_align, req), 1)
-		 /* and the ip is in the lease range */
+		 /* and the IP is in the lease range */
 		 && ntohl(req_align) >= server_config.start_ip
 		 && ntohl(req_align) <= server_config.end_ip
 		 /* and is not already taken/offered */
@@ -137,9 +147,10 @@ int FAST_FUNC send_offer(struct dhcpMessage *oldpacket)
 			|| lease_expired(lease))
 		) {
 			packet.yiaddr = req_align;
-		/* otherwise, find a free IP */
-		} else {
-			packet.yiaddr = find_free_or_expired_address();
+		}
+		/* Otherwise, find a free IP */
+		else {
+			packet.yiaddr = find_free_or_expired_address(oldpacket->chaddr);
 		}
 
 		if (!packet.yiaddr) {