Fix MDB-signal process and add TAP test for feature

Author: reshke

src/backend/storage/ipc/signalfuncs.c

@@ -93,8 +93,10 @@ pg_signal_backend(int pid, int sig)
 	 */
 
 	/* We allow to kill queries issued with MDB prefix */
-	if (!superuser() && !OidIsValid(proc->roleId))
+	if (!superuser() && OidIsValid(proc->roleId))
 	{
+		/* Ok, we are not superuser, and we try to kill 
+		* some backend, which can may be a MDB-cancellable query*/
 		LocalPgBackendStatus *local_beentry;
 		char * appname = NULL;
 		local_beentry = pgstat_get_local_beentry_by_proc_number(GetNumberFromPGProc(proc));

src/test/mdb_admin/t/mdb_app_name.pl

@@ -0,0 +1,75 @@
+
+# Copyright (c) 2024-2024, MDB, Mother Russia
+
+# Minimal test testing streaming replication
+use strict;
+use warnings;
+use PostgreSQL::Test::Cluster;
+use PostgreSQL::Test::Utils;
+use Test::More;
+
+# Initialize primary node
+my $node_primary = PostgreSQL::Test::Cluster->new('primary');
+$node_primary->init();
+$node_primary->start;
+
+# Create some content on primary and check its presence in standby nodes
+$node_primary->safe_psql('postgres',
+	"
+    CREATE DATABASE regress;
+    CREATE ROLE mdb_reg_lh_app_name;
+    GRANT pg_signal_backend to mdb_reg_lh_app_name;
+    CREATE TABLE mdb_app_name_t(i int);
+");
+
+my $main_sess = $node_primary->background_psql('postgres');
+
+$main_sess->query_safe(
+	q(
+SET application_name TO 'SU';
+BEGIN;
+INSERT INTO mdb_app_name_t VALUES(0);
+));
+
+
+my $res_pid = $node_primary->safe_psql('regress',
+	"
+    SELECT pid FROM pg_stat_activity WHERE application_name = 'SU';
+");
+
+print "pid is $res_pid\n";
+
+ok(1);
+
+
+my ($res_reg_lh_1, $stdout_reg_lh_1, $stderr_reg_lh_1)  = $node_primary->psql('regress',
+	"
+    SET ROLE mdb_reg_lh_app_name;
+    SELECT pg_terminate_backend($res_pid);
+");
+
+# print ($res_reg_lh_1, $stdout_reg_lh_1, $stderr_reg_lh_1, "\n");
+
+ok($res_reg_lh_1 != 0, "should fail for non-MDB");
+like($stderr_reg_lh_1, qr/Only roles with the SUPERUSER attribute may terminate processes of roles with the SUPERUSER attribute./, "matches");
+
+# should succeed
+$main_sess->query_safe(qq[COMMIT]);
+
+$main_sess->query_safe(
+	q(
+SET application_name TO 'MDB';
+BEGIN;
+INSERT INTO mdb_app_name_t VALUES(1);
+));
+
+
+my ($res_reg_lh_2, $stdout_reg_lh_2, $stderr_reg_lh_2) = $node_primary->psql('regress',
+	"
+    SET ROLE mdb_reg_lh_app_name;
+    SELECT pg_terminate_backend($res_pid);
+");
+
+ok($res_reg_lh_2 == 0, "should success for MDB");
+
+done_testing();