repmgrd: improve walsender disable check

Specifically, don't attempt to disable walsenders if "standby_disconnect_on_failover"
is "true", but the repmgr user is not a superuser.

This restriction can be lifted from PostgreSQL 15.

HISTORY

@@ -2,6 +2,7 @@
         standby clone: don't error out if unable to determine cluster size (Ian)
         node check: fix --downstream --nagios output; GitHub #749 (Ian)
         repmgrd: ensure witness node marked active (hslightdb)
+        repmgrd: improve walsender disable check (Ian)
 
 5.3.1   2022-02-15
         repmgrd: fixes for potential connection leaks (hslightdb)

dbutils.c

@@ -1888,6 +1888,42 @@ can_execute_pg_promote(PGconn *conn)
 }
 
 
+/*
+ * Determine if the user associated with the current connection
+ * has sufficient permissions to disable the walsender
+ */
+bool
+can_disable_walsender(PGconn *conn)
+{
+	/*
+	 * Requires PostgreSQL 9.5 or later, because ALTER SYSTEM
+	 */
+	if (PQserverVersion(conn) < 90500)
+	{
+		log_warning(_("\"standby_disconnect_on_failover\" specified, but not available for this PostgreSQL version"));
+		/* TODO: format server version */
+		log_detail(_("available from PostgreSQL 9.5; this PostgreSQL version is %i"), PQserverVersion(conn));
+
+		return false;
+	}
+
+	/*
+	 * Superusers can do anything
+	 */
+	if (is_superuser_connection(conn, NULL) == true)
+		return true;
+
+	/*
+	 * As of PostgreSQL 14, it is not possible for a non-superuser
+	 * to execute ALTER SYSTEM, so further checks are superfluous.
+	 * This will need modifying for PostgreSQL 15.
+	 */
+	log_warning(_("\"standby_disconnect_on_failover\" specified, but repmgr user is not a superuser"));
+	log_detail(_("superuser permission required to disable standbys on failover"));
+
+	return false;
+}
+
 /*
  * Determine if the user associated with the current connection is
  * a member of the "pg_monitor" default role, or optionally one

dbutils.h

@@ -454,6 +454,7 @@ pid_t		get_wal_receiver_pid(PGconn *conn);
 
 /* user/role information functions */
 bool		can_execute_pg_promote(PGconn *conn);
+bool		can_disable_walsender(PGconn *conn);
 bool		connection_has_pg_monitor_role(PGconn *conn, const char *subrole);
 bool		is_replication_role(PGconn *conn, char *rolname);
 bool		is_superuser_connection(PGconn *conn, t_connection_user *userinfo);

doc/appendix-release-notes.xml

@@ -53,6 +53,12 @@
               GitHub #754.
             </para>
           </listitem>
+          <listitem>
+            <para>
+              &repmgrd;: if <varname>standby_disconnect_on_failover</varname> is set, verify
+              &repmgr; is a superuser before attempting to disable the WAL receiver.
+            </para>
+          </listitem>
         </itemizedlist>
       </para>
     </sect2>

repmgrd-physical.c

@@ -2862,6 +2862,7 @@ do_primary_failover(void)
 	bool final_result = false;
 	NodeInfoList sibling_nodes = T_NODE_INFO_LIST_INITIALIZER;
 	int new_primary_id = UNKNOWN_NODE_ID;
+	bool standby_disconnect_on_failover = false;
 
 	/*
 	 * Double-check status of the local connection
@@ -2874,20 +2875,20 @@ do_primary_failover(void)
 	 */
 	if (config_file_options.standby_disconnect_on_failover == true)
 	{
-		NodeInfoListCell *cell = NULL;
-		NodeInfoList check_sibling_nodes = T_NODE_INFO_LIST_INITIALIZER;
-		int i;
+		/*
+		 * Determine whether we can actually disable the walsender; this depends
+		 * on PostgreSQL version and user permissions.
+		 */
+		standby_disconnect_on_failover = can_disable_walsender(local_conn);
 
-		bool sibling_node_wal_receiver_connected = false;
+		if (standby_disconnect_on_failover == true)
+		{
+			NodeInfoListCell *cell = NULL;
+			NodeInfoList check_sibling_nodes = T_NODE_INFO_LIST_INITIALIZER;
+			int i;
+
+			bool sibling_node_wal_receiver_connected = false;
 
-		if (PQserverVersion(local_conn) < 90500)
-		{
-			log_warning(_("\"standby_disconnect_on_failover\" specified, but not available for this PostgreSQL version"));
-			/* TODO: format server version */
-			log_detail(_("available from PostgreSQL 9.5, this PostgreSQL version is %i"), PQserverVersion(local_conn));
-		}
-		else
-		{
 			disable_wal_receiver(local_conn);
 
 			/*
@@ -2971,7 +2972,7 @@ do_primary_failover(void)
 	log_debug("election result: %s", _print_election_result(election_result));
 
 	/* Reenable WAL receiver, if disabled */
-	if (config_file_options.standby_disconnect_on_failover == true)
+	if (standby_disconnect_on_failover == true)
 	{
 		/* adjust "wal_retrieve_retry_interval" but don't wait for WAL receiver to start */
 		enable_wal_receiver(local_conn, false);