From: Mark Andrews <marka@isc.org>
Date: Tue, 22 Sep 2020 06:24:06 +0000 (+1000)
Subject: Address lock-order-inversion
X-Git-Tag: v9.17.6~40^2
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=1090876693470eedf69211d0fe71ba2c88160f45;p=thirdparty%2Fbind9.git

Address lock-order-inversion

    WARNING: ThreadSanitizer: lock-order-inversion (potential deadlock)
    Cycle in lock order graph: M1 (0x000000000001) => M2 (0x000000000002) => M1

    Mutex M2 acquired here while holding mutex M1 in thread T1:
    #0 pthread_rwlock_wrlock <null>
    #1 isc_rwlock_lock lib/isc/rwlock.c:52:4
    #2 zone_postload lib/dns/zone.c:5101:2
    #3 receive_secure_db lib/dns/zone.c:16206:11
    #4 dispatch lib/isc/task.c:1152:7
    #5 run lib/isc/task.c:1344:2

    Mutex M1 previously acquired by the same thread here:
    #0 pthread_mutex_lock <null>
    #1 receive_secure_db lib/dns/zone.c:16204:2
    #2 dispatch lib/isc/task.c:1152:7
    #3 run lib/isc/task.c:1344:2

    Mutex M1 acquired here while holding mutex M2 in thread T1:
    #0 pthread_mutex_lock <null>
    #1 get_raw_serial lib/dns/zone.c:2518:2
    #2 zone_gotwritehandle lib/dns/zone.c:2559:4
    #3 dispatch lib/isc/task.c:1152:7
    #4 run lib/isc/task.c:1344:2

    Mutex M2 previously acquired by the same thread here:
    #0 pthread_rwlock_rdlock <null>
    #1 isc_rwlock_lock lib/isc/rwlock.c:48:3
    #2 zone_gotwritehandle lib/dns/zone.c:2552:2
    #3 dispatch lib/isc/task.c:1152:7
    #4 run lib/isc/task.c:1344:2

    Thread T1 (running) created by main thread at:
    #0 pthread_create <null>
    #1 isc_thread_create lib/isc/pthreads/thread.c:73:8
    #2 isc_taskmgr_create lib/isc/task.c:1434:3
    #3 create_managers bin/named/main.c:915:11
    #4 setup bin/named/main.c:1223:11
    #5 main bin/named/main.c:1523:2

    SUMMARY: ThreadSanitizer: lock-order-inversion (potential deadlock) in pthread_rwlock_wrlock
---

diff --git a/lib/dns/zone.c b/lib/dns/zone.c
index eb300e1bfc3..fc522a90744 100644
--- a/lib/dns/zone.c
+++ b/lib/dns/zone.c
@@ -2534,6 +2534,7 @@ zone_gotwritehandle(isc_task_t *task, isc_event_t *event) {
 	isc_result_t result = ISC_R_SUCCESS;
 	dns_dbversion_t *version = NULL;
 	dns_masterrawheader_t rawdata;
+	dns_db_t *db = NULL;
 
 	REQUIRE(DNS_ZONE_VALID(zone));
 	INSIST(task == zone->task);
@@ -2551,9 +2552,12 @@ zone_gotwritehandle(isc_task_t *task, isc_event_t *event) {
 	INSIST(zone != zone->raw);
 	ZONEDB_LOCK(&zone->dblock, isc_rwlocktype_read);
 	if (zone->db != NULL) {
+		dns_db_attach(zone->db, &db);
+	}
+	ZONEDB_UNLOCK(&zone->dblock, isc_rwlocktype_read);
+	if (db != NULL) {
 		const dns_master_style_t *output_style;
-
-		dns_db_currentversion(zone->db, &version);
+		dns_db_currentversion(db, &version);
 		dns_master_initrawheader(&rawdata);
 		if (inline_secure(zone)) {
 			get_raw_serial(zone->raw, &rawdata);
@@ -2566,14 +2570,16 @@ zone_gotwritehandle(isc_task_t *task, isc_event_t *event) {
 			output_style = &dns_master_style_default;
 		}
 		result = dns_master_dumpinc(
-			zone->mctx, zone->db, version, output_style,
-			zone->masterfile, zone->task, dump_done, zone,
-			&zone->dctx, zone->masterformat, &rawdata);
-		dns_db_closeversion(zone->db, &version, false);
+			zone->mctx, db, version, output_style, zone->masterfile,
+			zone->task, dump_done, zone, &zone->dctx,
+			zone->masterformat, &rawdata);
+		dns_db_closeversion(db, &version, false);
 	} else {
 		result = ISC_R_CANCELED;
 	}
-	ZONEDB_UNLOCK(&zone->dblock, isc_rwlocktype_read);
+	if (db != NULL) {
+		dns_db_detach(&db);
+	}
 	UNLOCK_ZONE(zone);
 	if (result != DNS_R_CONTINUE) {
 		goto fail;