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Fix UDP checksum handling in clinat.c

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#1037
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laviniuc 2026-05-19 11:00:01 +03:00 committed by GitHub
parent 2b8afc6c68
commit 1be394ed91
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1 changed files with 16 additions and 1 deletions
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17
src/openvpn/clinat.c
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@ -258,7 +258,22 @@ client_nat_transform(const struct client_nat_option_list *list, struct buffer *i
{
if (BLENZ(ipbuf) >= sizeof(struct openvpn_iphdr) + sizeof(struct openvpn_udphdr))
{
ADJUST_CHECKSUM(accumulate, h->u.udp.check);
/* RFC 768: a UDP checksum of 0 means "no checksum computed".
* Do not run the incremental adjustment over a non-checksum,
* or we will write a bogus non-zero value into the field. */
if (h->u.udp.check != 0)
{
ADJUST_CHECKSUM(accumulate, h->u.udp.check);
/* RFC 768: a computed checksum of 0 must be transmitted
* as 0xFFFF, because 0 is reserved to mean "no checksum". */
if (h->u.udp.check == 0)
{
h->u.udp.check = 0xFFFF;
}
}
}
}
}