fix: Address potential TSAN issue with find->status

find->status is a private field of dns_adbfind_t so it now has an accessor function and has been made atomic.

Closes #4802

Merge branch '4802-address-potential-tsan-issue-with-find-status' into 'main'

Closes #4802

See merge request isc-projects/bind9!9137

lib/dns/adb.c

@@ -935,7 +935,7 @@ clean_finds_at_name(dns_adbname_t *name, dns_adbstatus_t astat,
 
 			INSIST(!FIND_EVENTSENT(find));
 
-			find->status = astat;
+			atomic_store(&find->status, astat);
 
 			DP(DEF_LEVEL, "cfan: sending find %p to caller", find);
 
@@ -2222,7 +2222,7 @@ post_copy:
 	if (want_event) {
 		INSIST((find->flags & DNS_ADBFIND_ADDRESSMASK) != 0);
 		find->loop = loop;
-		find->status = DNS_ADB_UNSET;
+		atomic_store(&find->status, DNS_ADB_UNSET);
 		find->cb = cb;
 		find->cbarg = cbarg;
 	}
@@ -2276,7 +2276,7 @@ dns_adb_destroyfind(dns_adbfind_t **findp) {
 static void
 find_sendevent(dns_adbfind_t *find) {
 	if (!FIND_EVENTSENT(find)) {
-		find->status = DNS_ADB_CANCELED;
+		atomic_store(&find->status, DNS_ADB_CANCELED);
 
 		DP(DEF_LEVEL, "sending find %p to caller", find);
 
@@ -2321,6 +2321,13 @@ dns_adb_cancelfind(dns_adbfind_t *find) {
 	}
 }
 
+unsigned int
+dns_adb_findstatus(dns_adbfind_t *find) {
+	REQUIRE(DNS_ADBFIND_VALID(find));
+
+	return (atomic_load(&find->status));
+}
+
 void
 dns_adb_dump(dns_adb_t *adb, FILE *f) {
 	isc_stdtime_t now = isc_stdtime_now();

lib/dns/include/dns/adb.h

@@ -121,15 +121,15 @@ struct dns_adbfind {
 	ISC_LINK(dns_adbfind_t) publink;      /*%< RW: client use */
 
 	/* Private */
-	isc_mutex_t	lock; /* locks all below */
-	in_port_t	port;
-	unsigned int	flags;
-	dns_adbname_t  *adbname;
-	dns_adb_t      *adb;
-	isc_loop_t     *loop;
-	dns_adbstatus_t status;
-	isc_job_cb	cb;
-	void	       *cbarg;
+	isc_mutex_t		 lock; /* locks all below */
+	in_port_t		 port;
+	unsigned int		 flags;
+	dns_adbname_t		*adbname;
+	dns_adb_t		*adb;
+	isc_loop_t		*loop;
+	_Atomic(dns_adbstatus_t) status;
+	isc_job_cb		 cb;
+	void			*cbarg;
 	ISC_LINK(dns_adbfind_t) plink;
 };
 
@@ -387,6 +387,16 @@ dns_adbfind_done(dns_adbfind_t find);
  *\li	'find' != NULL and *find be valid dns_adbfind_t pointer.
  */
 
+unsigned int
+dns_adb_findstatus(dns_adbfind_t *);
+/*%<
+ * Returns the status field of the find.
+ *
+ * Requires:
+ *
+ *\li	'find' be a valid dns_adbfind_t pointer.
+ */
+
 void
 dns_adb_destroyfind(dns_adbfind_t **find);
 /*%<

lib/dns/resolver.c

@@ -2907,7 +2907,7 @@ fctx_finddone(void *arg) {
 		 * The fetch is waiting for a name to be found.
 		 */
 		INSIST(!SHUTTINGDOWN(fctx));
-		if (find->status == DNS_ADB_MOREADDRESSES) {
+		if (dns_adb_findstatus(find) == DNS_ADB_MOREADDRESSES) {
 			FCTX_ATTR_CLR(fctx, FCTX_ATTR_ADDRWAIT);
 			want_try = true;
 		} else {