udhcp: fix oversized packet sending (introduced by "slack for bad dhcp servers" options);

slight optimizations and function renaming

udhcp_send_raw_packet                                  -     391    +391
udhcp_send_kernel_packet                               -     197    +197
udhcp_recv_packet                                      -     134    +134
get_raw_packet                                       353     326     -27
udhcp_get_packet                                     134       -    -134
udhcp_kernel_packet                                  197       -    -197
udhcp_raw_packet                                     391       -    -391
------------------------------------------------------------------------------
(add/remove: 3/3 grow/shrink: 0/1 up/down: 722/-749)          Total: -27 bytes

networking/udhcp/clientpacket.c

@@ -86,7 +86,7 @@ int send_decline(uint32_t xid, uint32_t server)
 
 	bb_info_msg("Sending decline...");
 
-	return udhcp_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
+	return udhcp_send_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
 		SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
 }
 #endif
@@ -106,7 +106,7 @@ int send_discover(uint32_t xid, uint32_t requested)
 	add_simple_option(packet.options, DHCP_MAX_SIZE, htons(576));
 	add_requests(&packet);
 	bb_info_msg("Sending discover...");
-	return udhcp_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
+	return udhcp_send_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
 			SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
 }
 
@@ -126,7 +126,7 @@ int send_selecting(uint32_t xid, uint32_t server, uint32_t requested)
 	add_requests(&packet);
 	addr.s_addr = requested;
 	bb_info_msg("Sending select for %s...", inet_ntoa(addr));
-	return udhcp_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
+	return udhcp_send_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
 				SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
 }
 
@@ -143,9 +143,9 @@ int send_renew(uint32_t xid, uint32_t server, uint32_t ciaddr)
 	add_requests(&packet);
 	bb_info_msg("Sending renew...");
 	if (server)
-		return udhcp_kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT);
+		return udhcp_send_kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT);
 
-	return udhcp_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
+	return udhcp_send_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
 				SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
 }
 
@@ -163,7 +163,7 @@ int send_release(uint32_t server, uint32_t ciaddr)
 	add_simple_option(packet.options, DHCP_SERVER_ID, server);
 
 	bb_info_msg("Sending release...");
-	return udhcp_kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT);
+	return udhcp_send_kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT);
 }
 
 
@@ -172,7 +172,6 @@ int get_raw_packet(struct dhcpMessage *payload, int fd)
 {
 	int bytes;
 	struct udp_dhcp_packet packet;
-	uint32_t source, dest;
 	uint16_t check;
 
 	memset(&packet, 0, sizeof(struct udp_dhcp_packet));
@@ -207,36 +206,31 @@ int get_raw_packet(struct dhcpMessage *payload, int fd)
 		return -2;
 	}
 
-	/* check IP checksum */
+	/* verify IP checksum */
 	check = packet.ip.check;
 	packet.ip.check = 0;
-	if (check != udhcp_checksum(&(packet.ip), sizeof(packet.ip))) {
+	if (check != udhcp_checksum(&packet.ip, sizeof(packet.ip))) {
-		DEBUG("bad IP header checksum, ignoring");
+		DEBUG("Bad IP header checksum, ignoring");
 		return -1;
 	}
 
-	/* verify the UDP checksum by replacing the header with a pseudo header */
+	/* verify UDP checksum. IP header has to be modified for this */
-	source = packet.ip.saddr;
+	memset(&packet.ip, 0, offsetof(struct iphdr, protocol));
-	dest = packet.ip.daddr;
+	/* fields which are not memset: protocol, check, saddr, daddr */
+	packet.ip.tot_len = packet.udp.len; /* yes, this is needed */
 	check = packet.udp.check;
 	packet.udp.check = 0;
-	memset(&packet.ip, 0, sizeof(packet.ip));
-
-	packet.ip.protocol = IPPROTO_UDP;
-	packet.ip.saddr = source;
-	packet.ip.daddr = dest;
-	packet.ip.tot_len = packet.udp.len; /* cheat on the psuedo-header */
 	if (check && check != udhcp_checksum(&packet, bytes)) {
 		bb_error_msg("packet with bad UDP checksum received, ignoring");
 		return -2;
 	}
 
-	memcpy(payload, &(packet.data), bytes - (sizeof(packet.ip) + sizeof(packet.udp)));
+	memcpy(payload, &packet.data, bytes - (sizeof(packet.ip) + sizeof(packet.udp)));
 
 	if (payload->cookie != htonl(DHCP_MAGIC)) {
 		bb_error_msg("received bogus message (bad magic) - ignoring");
 		return -2;
 	}
-	DEBUG("oooooh!!! got some!");
+	DEBUG("Got valid DHCP packet");
 	return bytes - (sizeof(packet.ip) + sizeof(packet.udp));
 }

networking/udhcp/common.h

@@ -54,14 +54,16 @@ struct BUG_bad_sizeof_struct_udp_dhcp_packet {
 		[(sizeof(struct udp_dhcp_packet) != 576 + CONFIG_UDHCPC_SLACK_FOR_BUGGY_SERVERS) ? -1 : 1];
 };
 
-void udhcp_init_header(struct dhcpMessage *packet, char type);
-int udhcp_get_packet(struct dhcpMessage *packet, int fd);
 uint16_t udhcp_checksum(void *addr, int count);
-int udhcp_raw_packet(struct dhcpMessage *payload,
+
+void udhcp_init_header(struct dhcpMessage *packet, char type);
+
+int udhcp_recv_packet(struct dhcpMessage *packet, int fd);
+int udhcp_send_raw_packet(struct dhcpMessage *payload,
 		uint32_t source_ip, int source_port,
 		uint32_t dest_ip, int dest_port,
 		const uint8_t *dest_arp, int ifindex);
-int udhcp_kernel_packet(struct dhcpMessage *payload,
+int udhcp_send_kernel_packet(struct dhcpMessage *payload,
 		uint32_t source_ip, int source_port,
 		uint32_t dest_ip, int dest_port);
 

networking/udhcp/dhcpc.c

@@ -451,7 +451,7 @@ int udhcpc_main(int argc, char **argv)
 			/* A packet is ready, read it */
 
 			if (listen_mode == LISTEN_KERNEL)
-				len = udhcp_get_packet(&packet, sockfd);
+				len = udhcp_recv_packet(&packet, sockfd);
 			else len = get_raw_packet(&packet, sockfd);
 
 			if (len == -1 && errno != EINTR) {

networking/udhcp/dhcpd.c

@@ -133,7 +133,7 @@ int udhcpd_main(int argc, char **argv)
 		default: continue;	/* signal or error (probably EINTR) */
 		}
 
-		bytes = udhcp_get_packet(&packet, server_socket); /* this waits for a packet - idle */
+		bytes = udhcp_recv_packet(&packet, server_socket); /* this waits for a packet - idle */
 		if (bytes < 0) {
 			if (bytes == -1 && errno != EINTR) {
 				DEBUG("error on read, %s, reopening socket", strerror(errno));

networking/udhcp/dhcprelay.c

@@ -256,7 +256,7 @@ static void dhcprelay_loop(int *fds, int num_sockets, int max_socket, char **cli
 		if (select(max_socket + 1, &rfds, NULL, NULL, &tv) > 0) {
 			/* server */
 			if (FD_ISSET(fds[0], &rfds)) {
-				packlen = udhcp_get_packet(&dhcp_msg, fds[0]);
+				packlen = udhcp_recv_packet(&dhcp_msg, fds[0]);
 				if (packlen > 0) {
 					pass_back(&dhcp_msg, packlen, fds);
 				}

networking/udhcp/packet.c

@@ -39,7 +39,7 @@ void udhcp_init_header(struct dhcpMessage *packet, char type)
 
 
 /* read a packet from socket fd, return -1 on read error, -2 on packet error */
-int udhcp_get_packet(struct dhcpMessage *packet, int fd)
+int udhcp_recv_packet(struct dhcpMessage *packet, int fd)
 {
 #if 0
 	static const char broken_vendors[][8] = {
@@ -111,7 +111,7 @@ uint16_t udhcp_checksum(void *addr, int count)
 		/* Make sure that the left-over byte is added correctly both
 		 * with little and big endian hosts */
 		uint16_t tmp = 0;
-		*(uint8_t *) (&tmp) = * (uint8_t *) source;
+		*(uint8_t*)&tmp = *(uint8_t*)source;
 		sum += tmp;
 	}
 	/*  Fold 32-bit sum to 16 bits */
@@ -123,7 +123,7 @@ uint16_t udhcp_checksum(void *addr, int count)
 
 
 /* Construct a ip/udp header for a packet, and specify the source and dest hardware address */
-int udhcp_raw_packet(struct dhcpMessage *payload,
+int udhcp_send_raw_packet(struct dhcpMessage *payload,
 		uint32_t source_ip, int source_port,
 		uint32_t dest_ip, int dest_port, const uint8_t *dest_arp, int ifindex)
 {
@@ -132,6 +132,11 @@ int udhcp_raw_packet(struct dhcpMessage *payload,
 	struct sockaddr_ll dest;
 	struct udp_dhcp_packet packet;
 
+	enum {
+		IP_UPD_DHCP_SIZE = sizeof(struct udp_dhcp_packet) - CONFIG_UDHCPC_SLACK_FOR_BUGGY_SERVERS,
+		UPD_DHCP_SIZE    = IP_UPD_DHCP_SIZE - offsetof(struct udp_dhcp_packet, udp),
+	};
+
 	fd = socket(PF_PACKET, SOCK_DGRAM, htons(ETH_P_IP));
 	if (fd < 0) {
 		bb_perror_msg("socket");
@@ -140,6 +145,7 @@ int udhcp_raw_packet(struct dhcpMessage *payload,
 
 	memset(&dest, 0, sizeof(dest));
 	memset(&packet, 0, sizeof(packet));
+	packet.data = *payload; /* struct copy */
 
 	dest.sll_family = AF_PACKET;
 	dest.sll_protocol = htons(ETH_P_IP);
@@ -157,19 +163,19 @@ int udhcp_raw_packet(struct dhcpMessage *payload,
 	packet.ip.daddr = dest_ip;
 	packet.udp.source = htons(source_port);
 	packet.udp.dest = htons(dest_port);
-	packet.udp.len = htons(sizeof(packet.udp) + sizeof(struct dhcpMessage)); /* cheat on the psuedo-header */
+	/* size, excluding IP header: */
+	packet.udp.len = htons(UPD_DHCP_SIZE);
+	/* for UDP checksumming, ip.len is set to UDP packet len */
 	packet.ip.tot_len = packet.udp.len;
-	memcpy(&(packet.data), payload, sizeof(struct dhcpMessage));
+	packet.udp.check = udhcp_checksum(&packet, IP_UPD_DHCP_SIZE);
-	packet.udp.check = udhcp_checksum(&packet, sizeof(struct udp_dhcp_packet));
+	/* but for sending, it is set to IP packet len */
-
+	packet.ip.tot_len = htons(IP_UPD_DHCP_SIZE);
-	packet.ip.tot_len = htons(sizeof(struct udp_dhcp_packet));
 	packet.ip.ihl = sizeof(packet.ip) >> 2;
 	packet.ip.version = IPVERSION;
 	packet.ip.ttl = IPDEFTTL;
-	packet.ip.check = udhcp_checksum(&(packet.ip), sizeof(packet.ip));
+	packet.ip.check = udhcp_checksum(&packet.ip, sizeof(packet.ip));
 
-	result = sendto(fd, &packet, sizeof(struct udp_dhcp_packet), 0,
+	result = sendto(fd, &packet, IP_UPD_DHCP_SIZE, 0, (struct sockaddr *) &dest, sizeof(dest));
-			(struct sockaddr *) &dest, sizeof(dest));
 	if (result <= 0) {
 		bb_perror_msg("sendto");
 	}
@@ -179,13 +185,17 @@ int udhcp_raw_packet(struct dhcpMessage *payload,
 
 
 /* Let the kernel do all the work for packet generation */
-int udhcp_kernel_packet(struct dhcpMessage *payload,
+int udhcp_send_kernel_packet(struct dhcpMessage *payload,
 		uint32_t source_ip, int source_port,
 		uint32_t dest_ip, int dest_port)
 {
 	int fd, result;
 	struct sockaddr_in client;
 
+	enum {
+		DHCP_SIZE = sizeof(struct dhcpMessage) - CONFIG_UDHCPC_SLACK_FOR_BUGGY_SERVERS,
+	};
+
 	fd = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
 	if (fd < 0)
 		return -1;
@@ -212,7 +222,7 @@ int udhcp_kernel_packet(struct dhcpMessage *payload,
 		return -1;
 	}
 
-	result = write(fd, payload, sizeof(struct dhcpMessage));
+	result = write(fd, payload, DHCP_SIZE);
 	close(fd);
 	return result;
 }

networking/udhcp/serverpacket.c

@@ -30,7 +30,7 @@ static int send_packet_to_relay(struct dhcpMessage *payload)
 {
 	DEBUG("Forwarding packet to relay");
 
-	return udhcp_kernel_packet(payload, server_config.server, SERVER_PORT,
+	return udhcp_send_kernel_packet(payload, server_config.server, SERVER_PORT,
 			payload->giaddr, SERVER_PORT);
 }
 
@@ -58,7 +58,7 @@ static int send_packet_to_client(struct dhcpMessage *payload, int force_broadcas
 		ciaddr = payload->yiaddr;
 		chaddr = payload->chaddr;
 	}
-	return udhcp_raw_packet(payload, server_config.server, SERVER_PORT,
+	return udhcp_send_raw_packet(payload, server_config.server, SERVER_PORT,
 			ciaddr, CLIENT_PORT, chaddr, server_config.ifindex);
 }