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Fix UDP checksum generation (0 -> 0xffff)

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See changelog and http://seclists.org/nmap-dev/2013/q4/122
This commit is contained in:
dmiller
2013-11-06 02:46:20 +00:00
parent bce4bcf7f9
commit 77f1429a56
2 changed files with 16 additions and 2 deletions
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13
libnetutil/netutil.cc
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@@ -844,7 +844,15 @@ unsigned short ipv4_pseudoheader_cksum(const struct in_addr *src,
sum = ip_cksum_add(hstart, len, sum);
/* Fold in the carry, take the complement, and return. */
return ip_cksum_carry(sum);
sum = ip_cksum_carry(sum);
/* RFC 768: "If the computed checksum is zero, it is transmitted as all
* ones (the equivalent in one's complement arithmetic). An all zero
* transmitted checksum value means that the transmitter generated no
* checksum" */
if (proto == IP_PROTO_UDP && sum == 0)
sum = 0xFFFF;
return sum;
}
/* Calculate the Internet checksum of some given data concatenated with the
@@ -868,6 +876,7 @@ u16 ipv6_pseudoheader_cksum(const struct in6_addr *src,
sum = ip_cksum_add(&hdr, sizeof(hdr), 0);
sum = ip_cksum_add(hstart, len, sum);
sum = ip_cksum_carry(sum);
/* RFC 2460: "Unlike IPv4, when UDP packets are originated by an IPv6 node,
the UDP checksum is not optional. That is, whenever originating a UDP
packet, an IPv6 node must compute a UDP checksum over the packet and the
@@ -876,7 +885,7 @@ u16 ipv6_pseudoheader_cksum(const struct in6_addr *src,
if (nxt == IP_PROTO_UDP && sum == 0)
sum = 0xFFFF;
return ip_cksum_carry(sum);
return sum;
}
void sethdrinclude(int sd) {