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Fix invalid checksum generation.

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Use equation 3 given in RFC 1624 and the UpdateTTL() example function given
RFC 1141.

# Conflicts:
#	src/route.c
This commit is contained in:
Nathan Stratton Treadway 2015-09-12 16:33:52 +02:00 • committed by Guus Sliepen
parent 56a8b90d86
commit ae89a25695
1 changed files with 5 additions and 3 deletions
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8
src/route.c
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@ -164,7 +164,7 @@ static void clamp_mss(const node_t *source, const node_t *via, vpn_packet_t *pac
/* Found it */
uint16_t oldmss = DATA(packet)[start + 22 + i] << 8 | DATA(packet)[start + 23 + i];
uint16_t newmss = mtu - start - 20;
uint16_t csum = DATA(packet)[start + 16] << 8 | DATA(packet)[start + 17];
uint32_t csum = DATA(packet)[start + 16] << 8 | DATA(packet)[start + 17];
if(oldmss <= newmss)
break;
@ -175,11 +175,13 @@ static void clamp_mss(const node_t *source, const node_t *via, vpn_packet_t *pac
DATA(packet)[start + 22 + i] = newmss >> 8;
DATA(packet)[start + 23 + i] = newmss & 0xff;
csum ^= 0xffff;
csum -= oldmss;
csum += oldmss ^ 0xffff;
csum += newmss;
csum = (csum & 0xffff) + (csum >> 16);
csum += csum >> 16;
csum ^= 0xffff;
DATA(packet)[start + 16] = csum >> 8;
DATA(packet)[start + 17] = csum & 0xff;
DATA(packet)[start + 17] = csum;
break;
}
}