SymbX/systemd
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

resolved: only send goodbye for the RRs of the service being unregistered

Browse Source 
dns_scope_announce(scope, /* goodbye= */ true) is not scoped to a
specific service: it walks the whole per-link mDNS zone and flags every
established RR as goodbye (TTL 0). Unregistering a single DNS-SD
service via the UnregisterService() D-Bus call hence withdrew the
host's own A/AAAA records and every other published service on the
link from remote caches, with nothing re-announcing them afterwards.

Introduce dns_scope_send_goodbye(), which sends an unsolicited response
for a caller-provided RR set, and let the DNS-SD unregistration path
send goodbye only for the RRs of the service actually being removed,
mirroring the flag logic of dns_scope_announce().

The goodbye answer is built per scope, and only includes records
actually established in the respective zone (or under re-verification,
in which case they are still served from it): a per-service goodbye
must take care not to withdraw records that are still being probed for
uniqueness, were withdrawn again after a conflict (in which case the
name belongs to the neighbor), or were never published in the scope in
the first place (e.g. on MulticastDNS=resolve links, which have an mDNS
scope but do not publish DNS-SD services).

This becomes more important with the next commit, which promotes
unregistration from an explicit method call to an automatic consequence
of the registering client disconnecting from the bus.
This commit is contained in:
Stefan Agner
2026-09-02 10:40:34 +02:00
parent 27ea9761ac
commit a3a8e82f25
3 changed files with 114 additions and 21 deletions
Download Patch File Download Diff File Expand all files Collapse all files
src/resolve/resolved-dns-scope.c
+36
View File
@@ -1533,6 +1533,42 @@ static int on_announcement_timeout(sd_event_source *s, usec_t usec, void *userda
return 0;
}
int dns_scope_send_goodbye(DnsScope *scope, DnsAnswer *answer) {
_cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
int r;
assert(scope);
assert(answer);
/* Sends an unsolicited response withdrawing the specified RRs, which are expected to be flagged as
* goodbye (TTL 0), without touching anything else published in the zone. */
if (scope->protocol != DNS_PROTOCOL_MDNS)
return 0;
r = sd_event_get_state(scope->manager->event);
if (r < 0)
return log_debug_errno(r, "Failed to get event loop state: %m");
/* If this is called on exit, through manager_free() -> link_free(), then we cannot announce. */
if (r == SD_EVENT_FINISHED)
return 0;
if (dns_answer_isempty(answer))
return 0;
r = dns_scope_make_reply_packet(scope, /* id= */ 0, DNS_RCODE_SUCCESS, /* q= */ NULL, answer,
/* soa= */ NULL, /* tentative= */ false, &p);
if (r < 0)
return log_debug_errno(r, "Failed to build reply packet: %m");
r = dns_scope_emit_udp(scope, -EBADF, AF_UNSPEC, p);
if (r < 0)
return log_debug_errno(r, "Failed to send reply packet: %m");
return 0;
}
int dns_scope_announce(DnsScope *scope, bool goodbye) {
_cleanup_(dns_answer_unrefp) DnsAnswer *answer = NULL;
_cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
src/resolve/resolved-dns-scope.h
+1
View File
@@ -114,6 +114,7 @@ int dns_scope_ifindex(DnsScope *s);
const char* dns_scope_ifname(DnsScope *s);
int dns_scope_announce(DnsScope *scope, bool goodbye);
int dns_scope_send_goodbye(DnsScope *scope, DnsAnswer *answer);
int dns_scope_add_dnssd_registered_services(DnsScope *scope);
int dns_scope_remove_dnssd_registered_services(DnsScope *scope);
src/resolve/resolved-dnssd.c
+77 -21
View File
@@ -6,6 +6,7 @@
#include "conf-files.h"
#include "conf-parser.h"
#include "constants.h"
#include "dns-answer.h"
#include "dns-domain.h"
#include "dns-rr.h"
#include "extract-word.h"
@@ -71,6 +72,67 @@ DnssdRegisteredService *dnssd_registered_service_free(DnssdRegisteredService *se
return mfree(service);
}
static int dnssd_registered_service_make_goodbye(
DnssdRegisteredService *service,
DnsScope *scope,
DnsAnswer **ret) {
_cleanup_(dns_answer_unrefp) DnsAnswer *answer = NULL;
size_t n_rrs = 3;
int r;
assert(service);
assert(scope);
assert(ret);
/* Collects those of the service's RRs that are established in the scope's zone (or under
* re-verification, in which case they are still served from the zone), flagged as goodbye (TTL 0),
* so that only this service is withdrawn, and only where we actually asserted ownership of the
* records, i.e. not while a record is still being probed for uniqueness, was withdrawn again after
* a conflict, or was never published in this scope in the first place. */
LIST_FOREACH(items, txt_data, service->txt_data_items)
n_rrs++;
answer = dns_answer_new(n_rrs);
if (!answer)
return -ENOMEM;
DnsResourceRecord *rrs[] = { service->ptr_rr, service->sub_ptr_rr, service->srv_rr };
FOREACH_ELEMENT(rr, rrs) {
if (!*rr)
continue;
DnsZoneItem *i = dns_zone_get(&scope->zone, *rr);
if (!i || !IN_SET(i->state, DNS_ZONE_ITEM_ESTABLISHED, DNS_ZONE_ITEM_VERIFYING))
continue;
r = dns_answer_add(answer, *rr, /* ifindex= */ 0,
dns_resource_key_is_dnssd_ptr((*rr)->key) ?
DNS_ANSWER_GOODBYE : (DNS_ANSWER_GOODBYE|DNS_ANSWER_CACHE_FLUSH),
/* rrsig= */ NULL);
if (r < 0)
return r;
}
LIST_FOREACH(items, txt_data, service->txt_data_items) {
if (!txt_data->rr)
continue;
DnsZoneItem *i = dns_zone_get(&scope->zone, txt_data->rr);
if (!i || !IN_SET(i->state, DNS_ZONE_ITEM_ESTABLISHED, DNS_ZONE_ITEM_VERIFYING))
continue;
r = dns_answer_add(answer, txt_data->rr, /* ifindex= */ 0,
DNS_ANSWER_GOODBYE|DNS_ANSWER_CACHE_FLUSH, /* rrsig= */ NULL);
if (r < 0)
return r;
}
*ret = TAKE_PTR(answer);
return 0;
}
void dnssd_registered_service_unregister(DnssdRegisteredService *service) {
Link *l;
int r;
@@ -82,32 +144,26 @@ void dnssd_registered_service_unregister(DnssdRegisteredService *service) {
/* Takes the service out of service: sends goodbye messages for it, removes its RRs from all mDNS
* zones, and drops it from the manager. Note that this also frees the passed object. */
HASHMAP_FOREACH(l, m->links) {
if (l->mdns_ipv4_scope) {
r = dns_scope_announce(l->mdns_ipv4_scope, /* goodbye= */ true);
HASHMAP_FOREACH(l, m->links)
FOREACH_ELEMENT(scope, ((DnsScope*[]) { l->mdns_ipv4_scope, l->mdns_ipv6_scope })) {
if (!*scope)
continue;
_cleanup_(dns_answer_unrefp) DnsAnswer *goodbye = NULL;
r = dnssd_registered_service_make_goodbye(service, *scope, &goodbye);
if (r >= 0)
r = dns_scope_send_goodbye(*scope, goodbye);
if (r < 0)
log_warning_errno(r, "Failed to send goodbye messages in IPv4 scope, ignoring: %m");
log_warning_errno(r, "Failed to send goodbye messages, ignoring: %m");
dns_zone_remove_rr(&l->mdns_ipv4_scope->zone, service->ptr_rr);
dns_zone_remove_rr(&l->mdns_ipv4_scope->zone, service->sub_ptr_rr);
dns_zone_remove_rr(&l->mdns_ipv4_scope->zone, service->srv_rr);
dns_zone_remove_rr(&(*scope)->zone, service->ptr_rr);
dns_zone_remove_rr(&(*scope)->zone, service->sub_ptr_rr);
dns_zone_remove_rr(&(*scope)->zone, service->srv_rr);
LIST_FOREACH(items, txt_data, service->txt_data_items)
dns_zone_remove_rr(&l->mdns_ipv4_scope->zone, txt_data->rr);
dns_zone_remove_rr(&(*scope)->zone, txt_data->rr);
}
if (l->mdns_ipv6_scope) {
r = dns_scope_announce(l->mdns_ipv6_scope, /* goodbye= */ true);
if (r < 0)
log_warning_errno(r, "Failed to send goodbye messages in IPv6 scope, ignoring: %m");
dns_zone_remove_rr(&l->mdns_ipv6_scope->zone, service->ptr_rr);
dns_zone_remove_rr(&l->mdns_ipv6_scope->zone, service->sub_ptr_rr);
dns_zone_remove_rr(&l->mdns_ipv6_scope->zone, service->srv_rr);
LIST_FOREACH(items, txt_data, service->txt_data_items)
dns_zone_remove_rr(&l->mdns_ipv6_scope->zone, txt_data->rr);
}
}
/* This drops the service from the manager's hashmap, hence the subsequent refresh will not simply
* add its RRs back. */
dnssd_registered_service_free(service);