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From 20424b3bfe8d3fae92c11a30e79aeffd26dc2891 Mon Sep 17 00:00:00 2001
From: Aram Sargsyan <aram@isc.org>
Date: Mon, 14 Nov 2022 12:18:06 +0000
Subject: [PATCH] Cancel all fetch events in dns_resolver_cancelfetch()
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)
---
lib/dns/resolver.c | 53 +++++++++++++++++++++++++++++++++++-----------
lib/ns/query.c | 4 +++-
2 files changed, 44 insertions(+), 13 deletions(-)
diff --git a/lib/dns/resolver.c b/lib/dns/resolver.c
index 18585b5..7cbfbb2 100644
--- a/lib/dns/resolver.c
+++ b/lib/dns/resolver.c
@@ -11254,8 +11254,9 @@ void
dns_resolver_cancelfetch(dns_fetch_t *fetch) {
fetchctx_t *fctx;
dns_resolver_t *res;
- dns_fetchevent_t *event, *next_event;
- isc_task_t *etask;
+ 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;
@@ -11267,32 +11268,60 @@ 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.
*/
- event = NULL;
if (fctx->state != fetchstate_done) {
+ dns_fetchevent_t *next_event = NULL;
for (event = ISC_LIST_HEAD(fctx->events); event != NULL;
event = next_event) {
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:
+ ISC_UNREACHABLE();
+ }
+ if (event_trystale != NULL &&
+ event_fetchdone != NULL)
+ {
+ break;
+ }
}
}
}
- if (event != NULL) {
- 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));
+ }
+
/*
* The fctx continues running even if no fetches remain;
* the answer is still cached.
*/
-
UNLOCK(&res->buckets[fctx->bucketnum].lock);
}
diff --git a/lib/ns/query.c b/lib/ns/query.c
index f66bab4..4f61374 100644
--- a/lib/ns/query.c
+++ b/lib/ns/query.c
@@ -6021,7 +6021,9 @@ 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;
}
--
2.39.1
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