openwrt/package/busybox/patches/950-partial-checksum.patch

--- a/networking/udhcp/dhcpc.c
+++ b/networking/udhcp/dhcpc.c
@@ -26,8 +26,8 @@
 #include "dhcpc.h"
 
 #include <netinet/if_ether.h>
-#include <netpacket/packet.h>
 #include <linux/filter.h>
+#include <linux/if_packet.h>
 
 /* struct client_config_t client_config is in bb_common_bufsiz1 */
 
@@ -846,17 +846,41 @@ static int send_release(uint32_t server,
 static NOINLINE int udhcp_recv_raw_packet(struct dhcp_packet *dhcp_pkt, int fd)
 {
 	int bytes;
+	int nocsum = 0;
 	struct ip_udp_dhcp_packet packet;
 	uint16_t check;
+	unsigned char cmsgbuf[CMSG_LEN(sizeof(struct tpacket_auxdata))];
+	struct iovec iov = {
+		.iov_base = &packet,
+		.iov_len = sizeof(packet),
+	};
+	struct msghdr msg = {
+		.msg_iov = &iov,
+		.msg_iovlen = 1,
+		.msg_control = cmsgbuf,
+		.msg_controllen = sizeof(cmsgbuf),
+	};
+	struct cmsghdr *cmsg;
 
 	memset(&packet, 0, sizeof(packet));
-	bytes = safe_read(fd, &packet, sizeof(packet));
+	do {
+		bytes = recvmsg(fd, &msg, 0);
+	} while (bytes < 0 && errno == EINTR);
+
 	if (bytes < 0) {
 		log1("Packet read error, ignoring");
 		/* NB: possible down interface, etc. Caller should pause. */
 		return bytes; /* returns -1 */
 	}
 
+	for (cmsg = CMSG_FIRSTHDR(&msg); cmsg; cmsg = CMSG_NXTHDR(&msg, cmsg)) {
+		if (cmsg->cmsg_level == SOL_PACKET &&
+			cmsg->cmsg_type == PACKET_AUXDATA) {
+			struct tpacket_auxdata *aux = (void *)CMSG_DATA(cmsg);
+			nocsum = aux->tp_status & TP_STATUS_CSUMNOTREADY;
+		}
+	}
+
 	if (bytes < (int) (sizeof(packet.ip) + sizeof(packet.udp))) {
 		log1("Packet is too short, ignoring");
 		return -2;
@@ -896,7 +920,7 @@ static NOINLINE int udhcp_recv_raw_packe
 	packet.ip.tot_len = packet.udp.len; /* yes, this is needed */
 	check = packet.udp.check;
 	packet.udp.check = 0;
-	if (check && check != udhcp_checksum(&packet, bytes)) {
+	if (!nocsum && check && check != udhcp_checksum(&packet, bytes)) {
 		log1("Packet with bad UDP checksum received, ignoring");
 		return -2;
 	}
@@ -942,6 +966,7 @@ static int udhcp_raw_socket(int ifindex)
 {
 	int fd;
 	struct sockaddr_ll sock;
+	int val;
 
 	/*
 	 * Comment:
@@ -1008,6 +1033,13 @@ static int udhcp_raw_socket(int ifindex)
 			log1("Attached filter to raw socket fd %d", fd); // log?
 	}
 
+	val = 1;
+	if (setsockopt(fd, SOL_PACKET, PACKET_AUXDATA, &val,
+			sizeof(val)) < 0) {
+		if (errno != ENOPROTOOPT)
+			log1("Failed to set auxiliary packet data for socket fd %d", fd);
+	}
+
 	log1("Created raw socket");
 
 	return fd;