autofs-5.1.8 - fix deadlock in lookups

From: Ian Kent <raven@themaw.net>

After adding locking to fix a crash during lookups we're seeing a
deadlock becuase of recursive calls.

But once the lookup is open we shouldn't need to open it again during
the recursive call, fix it based on that.

Signed-off-by: Ian Kent <raven@themaw.net>
---
 CHANGELOG           |    1 
 daemon/lookup.c     |   62 +++++++++++++++++++++++++++++++++-------------------
 daemon/master.c     |    8 ++++++
 include/master.h    |    1 
 modules/parse_amd.c |    2 -
 5 files changed, 51 insertions(+), 23 deletions(-)

--- autofs-5.1.7.orig/CHANGELOG
+++ autofs-5.1.7/CHANGELOG
@@ -117,6 +117,7 @@
 - don't immediately call function when waiting.
 - fix return status of mount_autofs().
 - don't close lookup at umount.
+- fix deadlock in lookups.
 
 25/01/2021 autofs-5.1.7
 - make bind mounts propagation slave by default.
--- autofs-5.1.7.orig/daemon/lookup.c
+++ autofs-5.1.7/daemon/lookup.c
@@ -318,31 +318,49 @@ static int do_read_map(struct autofs_poi
 	struct lookup_mod *lookup;
 	int status;
 
-	pthread_cleanup_push(map_module_lock_cleanup, map);
-	map_module_writelock(map);
-	if (!map->lookup) {
-		status = open_lookup(map->type, "", map->format,
-				     map->argc, map->argv, &lookup);
-		if (status == NSS_STATUS_SUCCESS)
-			map->lookup = lookup;
-		else
-			debug(ap->logopt,
-			      "lookup module %s open failed", map->type);
-	} else {
-		status = map->lookup->lookup_reinit(map->format,
-						    map->argc, map->argv,
-						    &map->lookup->context);
-		if (status)
-			warn(ap->logopt,
-			     "lookup module %s reinit failed", map->type);
-	}
-	pthread_cleanup_pop(1);
-	if (status != NSS_STATUS_SUCCESS)
-		return status;
-
 	if (!map->stale)
 		return NSS_STATUS_SUCCESS;
 
+	/* If this readmap is the result of trying to mount a submount
+	 * the readlock may already be held if the map is the same as
+	 * that of the caller. In that case the map has already been
+	 * read so just skip the map open/reinit.
+	 */
+	status = map_module_try_writelock(map);
+	if (status) {
+		if (!map->lookup) {
+			error(ap->logopt, "map module lock not held as expected");
+			return NSS_STATUS_UNAVAIL;
+		}
+	} else {
+		if (!map->lookup) {
+			pthread_cleanup_push(map_module_lock_cleanup, map);
+			status = open_lookup(map->type, "", map->format,
+					     map->argc, map->argv, &lookup);
+			pthread_cleanup_pop(0);
+			if (status != NSS_STATUS_SUCCESS) {
+				map_module_unlock(map);
+				debug(ap->logopt,
+				      "lookup module %s open failed", map->type);
+				return status;
+			}
+			map->lookup = lookup;
+		} else {
+			pthread_cleanup_push(map_module_lock_cleanup, map);
+			status = map->lookup->lookup_reinit(map->format,
+							    map->argc, map->argv,
+							    &map->lookup->context);
+			pthread_cleanup_pop(0);
+			if (status) {
+				map_module_unlock(map);
+				warn(ap->logopt,
+				     "lookup module %s reinit failed", map->type);
+				return status;
+			}
+		}
+		map_module_unlock(map);
+	}
+
 	master_source_current_wait(ap->entry);
 	ap->entry->current = map;
 
--- autofs-5.1.7.orig/daemon/master.c
+++ autofs-5.1.7/daemon/master.c
@@ -72,6 +72,14 @@ void map_module_writelock(struct map_sou
 		fatal(status);
 }
 
+int map_module_try_writelock(struct map_source *map)
+{
+	int status = pthread_rwlock_trywrlock(&map->module_lock);
+	if (status && status != EBUSY && status != EDEADLK)
+		fatal(status);
+	return status;
+}
+
 void map_module_readlock(struct map_source *map)
 {
 	int status = pthread_rwlock_rdlock(&map->module_lock);
--- autofs-5.1.7.orig/include/master.h
+++ autofs-5.1.7/include/master.h
@@ -128,6 +128,7 @@ int master_list_empty(struct master *);
 int master_done(struct master *);
 int master_kill(struct master *);
 void map_module_writelock(struct map_source *map);
+int map_module_try_writelock(struct map_source *map);
 void map_module_readlock(struct map_source *map);
 void map_module_unlock(struct map_source *map);
 void map_module_lock_cleanup(void *arg);
--- autofs-5.1.7.orig/modules/parse_amd.c
+++ autofs-5.1.7/modules/parse_amd.c
@@ -1391,7 +1391,7 @@ static int do_host_mount(struct autofs_p
 	cache_unlock(source->mc);
 
 	master_source_current_wait(ap->entry);
-	ap->entry->current = source;
+	ap->entry->current = instance;
 
 	map_module_readlock(instance);
 	lookup = instance->lookup;