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udp: Don't attempt to translate a 0.0.0.0 source address

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If an incoming packet has a source address of 0.0.0.0 we translate that to
the gateway address.  This doesn't really make sense, because we have no
way to do a reverse translation for reply packets.

Certain UDP protocols do use an unspecified source address in some
circumstances (e.g. DHCP).  These generally either require no reply, a
multicast reply, or provide a suitable reply address by other means.

In none of those cases does translating it in passt/pasta make sense.  The
best we can really do here is just leave it as is.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This commit is contained in:
David Gibson 2024-02-28 16:39:25 +11:00 committed by Stefano Brivio
parent bee61dd7d0
commit 720d777a69
1 changed files with 0 additions and 1 deletions
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udp.c
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@ -599,7 +599,6 @@ static size_t udp_update_hdr4(const struct ctx *c, int n, in_port_t dstport,
src_port == 53) {
b->iph.saddr = c->ip4.dns_match.s_addr;
} else if (IN4_IS_ADDR_LOOPBACK(&b->s_in.sin_addr) ||
IN4_IS_ADDR_UNSPECIFIED(&b->s_in.sin_addr)||
IN4_ARE_ADDR_EQUAL(&b->s_in.sin_addr, &c->ip4.addr_seen)) {
b->iph.saddr = c->ip4.gw.s_addr;
udp_tap_map[V4][src_port].ts = now->tv_sec;