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diff --git a/sbin/dhclient/packet.c b/sbin/dhclient/packet.c
--- a/sbin/dhclient/packet.c
+++ b/sbin/dhclient/packet.c
@@ -135,11 +135,14 @@
udp.uh_ulen = htons(sizeof(udp) + len);
memset(&udp.uh_sum, 0, sizeof(udp.uh_sum));
- udp.uh_sum = wrapsum(checksum((unsigned char *)&udp, sizeof(udp),
- checksum(data, len, checksum((unsigned char *)&ip.ip_src,
+ udp.uh_sum = wrapsum(checksum(data, len, checksum((unsigned char *)&udp,
+ sizeof(udp), checksum((unsigned char *)&ip.ip_src,
2 * sizeof(ip.ip_src),
IPPROTO_UDP + (u_int32_t)ntohs(udp.uh_ulen)))));
+ if (udp.uh_sum == htons(0))
+ udp.uh_sum = htons(0xffff);
+
memcpy(&buf[*bufix], &udp, sizeof(udp));
*bufix += sizeof(udp);
}
@@ -166,7 +169,7 @@
struct ip *ip;
struct udphdr *udp;
u_int32_t ip_len = (buf[bufix] & 0xf) << 2;
- u_int32_t sum, usum;
+ u_int32_t sum, usum, pseudo_sum;
static int ip_packets_seen;
static int ip_packets_bad_checksum;
static int udp_packets_seen;
@@ -224,23 +227,37 @@
}
usum = udp->uh_sum;
- udp->uh_sum = 0;
-
- sum = wrapsum(checksum((unsigned char *)udp, sizeof(*udp),
- checksum(data, len, checksum((unsigned char *)&ip->ip_src,
- 2 * sizeof(ip->ip_src),
- IPPROTO_UDP + (u_int32_t)ntohs(udp->uh_ulen)))));
-
udp_packets_seen++;
- if (usum && usum != sum) {
- udp_packets_bad_checksum++;
- if (udp_packets_seen > 4 && udp_packets_bad_checksum != 0 &&
- (udp_packets_seen / udp_packets_bad_checksum) < 2) {
- note("%d bad udp checksums in %d packets",
- udp_packets_bad_checksum, udp_packets_seen);
- udp_packets_seen = udp_packets_bad_checksum = 0;
+
+ if (usum != htons(0)) {
+ udp->uh_sum = 0;
+
+ pseudo_sum = checksum((unsigned char *)&ip->ip_src,
+ 2 * sizeof(ip->ip_src),
+ IPPROTO_UDP + (u_int32_t)ntohs(udp->uh_ulen));
+ sum = wrapsum(checksum(data, len,
+ checksum((unsigned char *)udp, sizeof(*udp), pseudo_sum)));
+ if (sum == htons(0))
+ sum = htons(0xffff);
+
+ /*
+ * In addition to accepting UDP packets with the correct
+ * checksum in the checksum field, accept also the ones which
+ * have the correct pseudo header checksum in the checksum
+ * field. This allows to process UDP packets, which have been
+ * marked for transmit checksum offloading by the sender side.
+ */
+ if (usum != sum && usum != htons(pseudo_sum & 0x0000ffff)) {
+ udp_packets_bad_checksum++;
+ if (udp_packets_seen > 4 &&
+ udp_packets_bad_checksum != 0 &&
+ (udp_packets_seen / udp_packets_bad_checksum) < 2) {
+ note("%d bad udp checksums in %d packets",
+ udp_packets_bad_checksum, udp_packets_seen);
+ udp_packets_seen = udp_packets_bad_checksum = 0;
+ }
+ return (-1);
}
- return (-1);
}
memcpy(&from->sin_port, &udp->uh_sport, sizeof(udp->uh_sport));

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