openwrt-xburst/package/busybox/patches/241-udhcpc-oversized_packets.patch

--- a/networking/udhcp/packet.c
+++ b/networking/udhcp/packet.c
@@ -165,6 +165,11 @@ uint16_t FAST_FUNC udhcp_checksum(void *
 	return ~sum;
 }
 
+int udhcp_get_payload_len(struct dhcp_packet *dhcp_pkt)
+{
+	return sizeof(struct dhcp_packet) - DHCP_OPTIONS_BUFSIZE + udhcp_end_option(dhcp_pkt->options) + sizeof(dhcp_pkt->options[0]);
+}
+
 /* Construct a ip/udp header for a packet, send packet */
 int FAST_FUNC udhcp_send_raw_packet(struct dhcp_packet *dhcp_pkt,
 		uint32_t source_nip, int source_port,
@@ -173,10 +178,10 @@ int FAST_FUNC udhcp_send_raw_packet(stru
 {
 	struct sockaddr_ll dest_sll;
 	struct ip_udp_dhcp_packet packet;
-	unsigned padding;
 	int fd;
 	int result = -1;
 	const char *msg;
+	int p_len = udhcp_get_payload_len(dhcp_pkt);
 
 	fd = socket(PF_PACKET, SOCK_DGRAM, htons(ETH_P_IP));
 	if (fd < 0) {
@@ -185,8 +190,8 @@ int FAST_FUNC udhcp_send_raw_packet(stru
 	}
 
 	memset(&dest_sll, 0, sizeof(dest_sll));
-	memset(&packet, 0, offsetof(struct ip_udp_dhcp_packet, data));
-	packet.data = *dhcp_pkt; /* struct copy */
+	memset(&packet, 0, sizeof(packet));
+	memcpy(&(packet.data), dhcp_pkt, p_len);
 
 	dest_sll.sll_family = AF_PACKET;
 	dest_sll.sll_protocol = htons(ETH_P_IP);
@@ -199,36 +204,24 @@ int FAST_FUNC udhcp_send_raw_packet(stru
 		goto ret_close;
 	}
 
-	/* We were sending full-sized DHCP packets (zero padded),
-	 * but some badly configured servers were seen dropping them.
-	 * Apparently they drop all DHCP packets >576 *ethernet* octets big,
-	 * whereas they may only drop packets >576 *IP* octets big
-	 * (which for typical Ethernet II means 590 octets: 6+6+2 + 576).
-	 *
-	 * In order to work with those buggy servers,
-	 * we truncate packets after end option byte.
-	 */
-	padding = DHCP_OPTIONS_BUFSIZE - 1 - udhcp_end_option(packet.data.options);
-
 	packet.ip.protocol = IPPROTO_UDP;
 	packet.ip.saddr = source_nip;
 	packet.ip.daddr = dest_nip;
 	packet.udp.source = htons(source_port);
 	packet.udp.dest = htons(dest_port);
-	/* size, excluding IP header: */
-	packet.udp.len = htons(UDP_DHCP_SIZE - padding);
-	/* for UDP checksumming, ip.len is set to UDP packet len */
+	p_len += sizeof(packet.udp);
+	packet.udp.len = htons(p_len);
 	packet.ip.tot_len = packet.udp.len;
-	packet.udp.check = udhcp_checksum(&packet, IP_UDP_DHCP_SIZE - padding);
-	/* but for sending, it is set to IP packet len */
-	packet.ip.tot_len = htons(IP_UDP_DHCP_SIZE - padding);
+	p_len += sizeof(packet.ip);
+	packet.udp.check = udhcp_checksum(&packet, p_len);
+	packet.ip.tot_len = htons(p_len);
 	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));
 
 	udhcp_dump_packet(dhcp_pkt);
-	result = sendto(fd, &packet, IP_UDP_DHCP_SIZE - padding, /*flags:*/ 0,
+	result = sendto(fd, &packet, p_len, /*flags:*/ 0,
 			(struct sockaddr *) &dest_sll, sizeof(dest_sll));
 	msg = "sendto";
  ret_close:
@@ -246,7 +239,6 @@ int FAST_FUNC udhcp_send_kernel_packet(s
 		uint32_t dest_nip, int dest_port)
 {
 	struct sockaddr_in client;
-	unsigned padding;
 	int fd;
 	int result = -1;
 	const char *msg;
@@ -277,9 +269,7 @@ int FAST_FUNC udhcp_send_kernel_packet(s
 	}
 
 	udhcp_dump_packet(dhcp_pkt);
-
-	padding = DHCP_OPTIONS_BUFSIZE - 1 - udhcp_end_option(dhcp_pkt->options);
-	result = safe_write(fd, dhcp_pkt, DHCP_SIZE - padding);
+	result = safe_write(fd, dhcp_pkt, udhcp_get_payload_len(dhcp_pkt));
 	msg = "write";
  ret_close:
 	close(fd);