resolved: actually unregister DNS-SD services when the D-Bus client vanishes (#43578)
Since the D-Bus DNS-SD API was introduced in c3036641f0ed (v236), `RegisterService()` has created an `sd_bus_track` object to destroy the registered service when the registering client disconnects from the bus. However, the track object is a `_cleanup_(sd_bus_track_unrefp)` local in `bus_method_register_service()` that is never stored anywhere, so it is destroyed again as soon as the method handler returns. The vanish handler (`dnssd_registered_service_on_bus_track()`) has thus been dead code for the past ~8 years. The observable effect: services registered via D-Bus silently persist after the client disconnects — unowned, advertised until resolved exits, and impossible to re-register since the identifier stays taken (`DNSSD_SERVICE_EXISTS`). At the same time, the registration doesn't survive a resolved restart, so the current behavior is neither reliably ephemeral nor reliably persistent. Noticed while reviewing a project that (unknowingly relying on this bug) registers a service with a one-shot `gdbus call` and expects it to persist. This PR: 1. splits the goodbye/zone-removal logic out of `bus_dnssd_method_unregister()` into a helper — the vanish path needs the full teardown, not just `dnssd_registered_service_free()`, which would leave the service's RRs published in the per-link mDNS zones; 2. stores the track object in `DnssdRegisteredService`, making client tracking work as originally intended; 3. documents the lifetime semantics in `org.freedesktop.resolve1(5)` (matching the equivalent Avahi D-Bus API, whose entry groups are likewise bound to the client connection) and points to `*.dnssd` files for registrations independent of a client's lifetime; 4. adds a TEST-75 case covering the connection-bound lifetime. Note this is a behavioral change for fire-and-forget clients (one-shot `busctl`/`gdbus` invocations). Arguably those were never working reliably (registrations silently vanished on any resolved restart, and stale entries blocked re-registration), but if this is deemed too risky, the alternative would be to drop the dead tracking code and codify the persist-until-exit behavior instead — I'd argue tracking as originally intended is the better contract. Verification: code compiles; the new integration test is included.
This commit is contained in:
Yu Watanabe
@@ -232,7 +232,7 @@ manual_testcase_01_resolvectl() {
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ip link add hoge.foo type dummy
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# Cleanup
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# shellcheck disable=SC2317
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# shellcheck disable=SC2317,SC2329
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cleanup() {
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ip link del hoge
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ip link del hoge.foo
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@@ -349,6 +349,7 @@ manual_testcase_02_mdns_llmnr() {
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ip link add hoge.foo type dummy
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# Cleanup
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# shellcheck disable=SC2317,SC2329
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cleanup() {
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rm -f /run/systemd/resolved.conf.d/90-mdns-llmnr.conf
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ip link del hoge
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@@ -436,6 +437,78 @@ manual_testcase_02_mdns_llmnr() {
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assert_in 'no' "$(resolvectl llmnr hoge)"
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}
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# Test for the D-Bus RegisterService()/UnregisterService() API
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manual_testcase_03_register_service() {
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local cursor_file="" invocation_id
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# Cleanup
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# shellcheck disable=SC2317,SC2329
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cleanup() {
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rm -f /run/systemd/resolved.conf.d/90-mdns.conf "${cursor_file:-}"
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ip link del mdns99 2>/dev/null || :
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systemctl reload systemd-resolved.service
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}
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trap cleanup RETURN ERR
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mkdir -p /run/systemd/resolved.conf.d
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{
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echo "[Resolve]"
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echo "MulticastDNS=yes"
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} >/run/systemd/resolved.conf.d/90-mdns.conf
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restart_resolved
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resolvectl log-level debug
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# resolved is restarted automatically if it crashes (Restart=always), which would let the checks below
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# pass for the wrong reason, so remember the invocation and verify it stayed the same at the end.
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invocation_id=$(systemctl show -P InvocationID systemd-resolved.service)
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# Make sure at least one link carries mDNS scopes, so that unregistration actually runs the
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# per-scope goodbye/zone teardown.
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ip link add mdns99 type dummy
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ip link set mdns99 up
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resolvectl mdns mdns99 yes
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cursor_file=$(mktemp)
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journalctl -n 0 --cursor-file="$cursor_file"
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# The lifetime of a registered service is bound to the bus connection of the client that registered
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# it. busctl disconnects right after the call, so the service should be unregistered again shortly
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# after. Wait for the vanish handler log message as proof that the client tracking triggered the
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# unregistration. See testcase_15_wait_online_dns() for why journalctl -f | grep -m1 is not used here.
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assert_in '/org/freedesktop/resolve1/dnssd/testservice' \
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"$(busctl call org.freedesktop.resolve1 /org/freedesktop/resolve1 org.freedesktop.resolve1.Manager \
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RegisterService 'sssqqqaa{say}' testservice '%H' _testservice._tcp 1234 0 0 0)"
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timeout 30 bash -c "until journalctl --after-cursor=\"\$(cat \"$cursor_file\")\" SYSLOG_IDENTIFIER=systemd-resolved --grep \"Client of DNS-SD service 'testservice' vanished, unregistering.\" >/dev/null 2>&1; do sleep .5; done"
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assert_not_in 'dnssd/testservice' "$(busctl tree org.freedesktop.resolve1)"
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# Unregistering it again should fail specifically because the service is gone (busctl prints the
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# D-Bus error message, not the error name), i.e. not because resolved crashed or the bus connection
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# failed.
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assert_in "DNS-SD service 'testservice' not known" \
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"$(busctl call org.freedesktop.resolve1 /org/freedesktop/resolve1 org.freedesktop.resolve1.Manager \
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UnregisterService 'o' /org/freedesktop/resolve1/dnssd/testservice 2>&1 || :)"
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# Re-registering the same identifier must succeed: before client tracking worked, the identifier
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# stayed taken by the vanished client's service and this failed with DNSSD_SERVICE_EXISTS. Take a
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# fresh cursor so the wait below cannot match the first round's identical message.
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rm -f "$cursor_file"
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journalctl -n 0 --cursor-file="$cursor_file"
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assert_in '/org/freedesktop/resolve1/dnssd/testservice' \
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"$(busctl call org.freedesktop.resolve1 /org/freedesktop/resolve1 org.freedesktop.resolve1.Manager \
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RegisterService 'sssqqqaa{say}' testservice '%H' _testservice._tcp 1234 0 0 0)"
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timeout 30 bash -c "until journalctl --after-cursor=\"\$(cat \"$cursor_file\")\" SYSLOG_IDENTIFIER=systemd-resolved --grep \"Client of DNS-SD service 'testservice' vanished, unregistering.\" >/dev/null 2>&1; do sleep .5; done"
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assert_not_in 'dnssd/testservice' "$(busctl tree org.freedesktop.resolve1)"
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# resolved must not have crashed and gotten restarted along the way.
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assert_eq "$(systemctl show -P InvocationID systemd-resolved.service)" "$invocation_id"
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systemctl is-active systemd-resolved.service
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}
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testcase_03_23951() {
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: "--- nss-resolve/nss-myhostname tests"
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@@ -866,7 +939,7 @@ testcase_08_resolved() {
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testcase_09_resolvectl_showcache() {
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# Cleanup
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# shellcheck disable=SC2317
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# shellcheck disable=SC2317,SC2329
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cleanup() {
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rm -f /run/systemd/resolved.conf.d/90-resolved.conf
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rm -f /run/systemd/network/10-dns2.netdev
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@@ -928,7 +1001,7 @@ testcase_10_resolvectl_json() {
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local status_json
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# Cleanup
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# shellcheck disable=SC2317
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# shellcheck disable=SC2317,SC2329
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cleanup() {
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rm -f /run/systemd/resolved.conf.d/90-fallback.conf
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systemctl reload systemd-resolved.service
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@@ -1099,7 +1172,7 @@ testcase_11_nft() {
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# Test resolvectl show-server-state
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testcase_12_resolvectl2() {
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# Cleanup
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# shellcheck disable=SC2317
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# shellcheck disable=SC2317,SC2329
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cleanup() {
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rm -f /run/systemd/resolved.conf.d/90-reload.conf
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systemctl reload systemd-resolved.service
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@@ -1201,7 +1274,7 @@ testcase_13_varlink_subscribe_dns_configuration() {
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fi
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# Cleanup
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# shellcheck disable=SC2317
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# shellcheck disable=SC2317,SC2329
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cleanup() {
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echo "===== io.systemd.Resolve.Monitor.SubscribeDNSConfiguration output: ====="
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cat "$tmpfile"
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@@ -1278,7 +1351,7 @@ testcase_13_varlink_subscribe_dns_configuration() {
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# Test RefuseRecordTypes
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testcase_14_refuse_record_types() {
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# shellcheck disable=SC2317
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# shellcheck disable=SC2317,SC2329
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cleanup() {
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rm -f /run/systemd/resolved.conf.d/90-refuserecords.conf
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restart_resolved
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@@ -1440,7 +1513,7 @@ testcase_14_refuse_record_types() {
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# Test systemd-networkd-wait-online interactions with systemd-resolved
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testcase_15_wait_online_dns() {
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# Cleanup
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# shellcheck disable=SC2317
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# shellcheck disable=SC2317,SC2329
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cleanup() {
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echo "===== journalctl -u $unit ====="
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journalctl -b --no-pager --no-hostname --full -u "$unit"
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@@ -1725,6 +1798,7 @@ systemctl enable --now systemd-resolved.service
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# Need to be run before SETUP, otherwise things will break
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manual_testcase_01_resolvectl
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manual_testcase_02_mdns_llmnr
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manual_testcase_03_register_service
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# Run setup
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setup
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