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Cancel all fetch events in dns_resolver_cancelfetch()

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Although 'dns_fetch_t' fetch can have two associated events, one for
each of 'DNS_EVENT_FETCHDONE' and 'DNS_EVENT_TRYSTALE' types, the
dns_resolver_cancelfetch() function is designed in a way that it
expects only one existing event, which it must cancel, and when it
happens so that 'stale-answer-client-timeout' is enabled and there
are two events, only one of them is canceled, and it results in an
assertion in dns_resolver_destroyfetch(), when it finds a dangling
event.

Change the logic of dns_resolver_cancelfetch() function so that it
cancels both the events (if they exist), and in the right order.

(cherry picked from commit ec2098ca35039e4f81fd0aa7c525eb960b8f47bf)
This commit is contained in:
Aram Sargsyan 2022-11-14 12:18:06 +00:00 committed by Michał Kępień
parent 72db6402f3
commit a4fc5e5158
2 changed files with 40 additions and 9 deletions
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45
lib/dns/resolver.c
View File

@ -10976,6 +10976,8 @@ dns_resolver_cancelfetch(dns_fetch_t *fetch) {
fetchctx_t *fctx = NULL;
dns_resolver_t *res = NULL;
dns_fetchevent_t *event = NULL;
dns_fetchevent_t *event_trystale = NULL;
dns_fetchevent_t *event_fetchdone = NULL;
REQUIRE(DNS_FETCH_VALID(fetch));
fctx = fetch->private;
@ -10987,9 +10989,9 @@ dns_resolver_cancelfetch(dns_fetch_t *fetch) {
LOCK(&res->buckets[fctx->bucketnum].lock);
/*
* Find the completion event for this fetch (as opposed
* Find the events for this fetch (as opposed
* to those for other fetches that have joined the same
* fctx) and send it with result = ISC_R_CANCELED.
* fctx) and send them with result = ISC_R_CANCELED.
*/
if (fctx->state != fetchstate_done) {
dns_fetchevent_t *next_event = NULL;
@ -10999,15 +11001,42 @@ dns_resolver_cancelfetch(dns_fetch_t *fetch) {
next_event = ISC_LIST_NEXT(event, ev_link);
if (event->fetch == fetch) {
ISC_LIST_UNLINK(fctx->events, event, ev_link);
break;
switch (event->ev_type) {
case DNS_EVENT_TRYSTALE:
INSIST(event_trystale == NULL);
event_trystale = event;
break;
case DNS_EVENT_FETCHDONE:
INSIST(event_fetchdone == NULL);
event_fetchdone = event;
break;
default:
UNREACHABLE();
}
if (event_trystale != NULL &&
event_fetchdone != NULL)
{
break;
}
}
}
}
if (event != NULL) {
isc_task_t *etask = event->ev_sender;
event->ev_sender = fctx;
event->result = ISC_R_CANCELED;
isc_task_sendanddetach(&etask, ISC_EVENT_PTR(&event));
/*
* The "trystale" event must be sent before the "fetchdone" event,
* because the latter clears the "recursing" query attribute, which is
* required by both events (handled by the same callback function).
*/
if (event_trystale != NULL) {
isc_task_t *etask = event_trystale->ev_sender;
event_trystale->ev_sender = fctx;
event_trystale->result = ISC_R_CANCELED;
isc_task_sendanddetach(&etask, ISC_EVENT_PTR(&event_trystale));
}
if (event_fetchdone != NULL) {
isc_task_t *etask = event_fetchdone->ev_sender;
event_fetchdone->ev_sender = fctx;
event_fetchdone->result = ISC_R_CANCELED;
isc_task_sendanddetach(&etask, ISC_EVENT_PTR(&event_fetchdone));
}
/*

4
lib/ns/query.c
View File

@ -6236,7 +6236,9 @@ fetch_callback(isc_task_t *task, isc_event_t *event) {
CTRACE(ISC_LOG_DEBUG(3), "fetch_callback");
if (event->ev_type == DNS_EVENT_TRYSTALE) {
query_lookup_stale(client);
if (devent->result != ISC_R_CANCELED) {
query_lookup_stale(client);
}
isc_event_free(ISC_EVENT_PTR(&event));
return;
}