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ipv6 udp checksums like ipv4 but with ipv6 pseudoheader

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this fixes a problem where both source and destination port are supplied on the commandline,
this lead to packets not showing up any more due to checksum being different.
this was mentioned first on https://github.com/traviscross/mtr/issues/351
This commit is contained in:
hiro 2021-11-09 17:50:12 +00:00
parent 3f80a21753
commit d6171b8df9
1 changed files with 18 additions and 11 deletions
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29
packet/construct_unix.c
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@ -306,18 +306,25 @@ int construct_udp6_packet(
set_udp_ports(udp, probe, param);
udp->length = htons(udp_size);
if (net_state->platform.ip6_socket_raw) {
/*
Instruct the kernel to put the pseudoheader checksum into the
UDP header, this is only needed when using RAW socket.
*/
int chksum_offset = (char *) &udp->checksum - (char *) udp;
if (setsockopt(udp_socket, IPPROTO_IPV6,
IPV6_CHECKSUM, &chksum_offset, sizeof(int))) {
return -1;
}
}
struct IP6PseudoHeader udph = {
.zero = {0,0,0},
.protocol = 17,
.len = udp->length
};
memcpy(udph.saddr, sockaddr_addr_offset(&probe->local_addr), 16);
memcpy(udph.daddr, sockaddr_addr_offset(&probe->remote_addr), 16);
/* get position to write checksum */
uint16_t *checksum_off = &udp->checksum;
if (udp->checksum != 0)
{ /* checksum is sequence number - correct the payload to match the checksum
checksum_off is udp payload */
checksum_off = (uint16_t *)&packet_buffer[sizeof(struct UDPHeader)];
}
*checksum_off = htons(udp4_checksum(&udph, udp,
sizeof(struct IP6PseudoHeader),
udp_size, udp->checksum != 0));
return 0;
}