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resolved: ignore mDNS replies from legacy mDNS ports

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mDNS replies always have to come from the mDNS port (unlike mDNS
queries, which are also allowed from non-mDNS ports). Hence refuse this.

Fixes: #33806
This commit is contained in:
Lennart Poettering
2025-06-05 18:51:34 +02:00
committed by Luca Boccassi
parent abe149d669
commit 373e6cdadb
1 changed files with 12 additions and 1 deletions
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13
src/resolve/resolved-mdns.c
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@@ -411,8 +411,10 @@ static int on_mdns_packet(sd_event_source *s, int fd, uint32_t revents, void *us
/* Refuse traffic from the local host, to avoid query loops. However, allow legacy mDNS
* unicast queries through anyway (we never send those ourselves, hence no risk).
* i.e. check for the source port nr. */
if (p->sender_port == MDNS_PORT && manager_packet_from_local_address(m, p))
if (p->sender_port == MDNS_PORT && manager_packet_from_local_address(m, p)) {
log_debug("Got mDNS UDP packet from local host, ignoring.");
return 0;
}
scope = manager_find_scope(m, p);
if (!scope) {
@@ -423,6 +425,15 @@ static int on_mdns_packet(sd_event_source *s, int fd, uint32_t revents, void *us
if (dns_packet_validate_reply(p) > 0) {
DnsResourceRecord *rr;
/* RFC 6762 section 6:
* The source UDP port in all Multicast DNS responses MUST be 5353 (the well-known port
* assigned to mDNS). Multicast DNS implementations MUST silently ignore any Multicast DNS
* responses they receive where the source UDP port is not 5353. */
if (p->sender_port != MDNS_PORT) {
log_debug("Got mDNS reply from non-mDNS port %u (not %i), ignoring.", p->sender_port, MDNS_PORT);
return 0;
}
log_debug("Got mDNS reply packet");
/*