Fix for CONC-627:

Don't substitute parameters in server error messages in
prepeated statement error handler function.

libmariadb/mariadb_stmt.c

@@ -106,6 +106,15 @@ void stmt_set_error(MYSQL_STMT *stmt,
     }
   }
 
+  /* Fix for CONC-627: If this is a server error message, we don't
+     need to substitute and possible variadic arguments will be
+     ignored */
+  if (!IS_MYSQL_ERROR(error_nr) && !IS_MARIADB_ERROR(error_nr))
+  {
+    strncpy(stmt->last_error, format, MYSQL_ERRMSG_SIZE - 1);
+    return;
+  }
+
   va_start(ap, format);
   vsnprintf(stmt->last_error, MYSQL_ERRMSG_SIZE - 1,
             format ? format : errmsg, ap);

unittest/libmariadb/ps_bugs.c

@@ -5487,7 +5487,28 @@ static int test_mdev19838(MYSQL *mysql)
   return OK;
 }
 
+static int test_conc627(MYSQL *mysql)
+{
+  MYSQL_STMT *stmt= mysql_stmt_init(mysql);
+  int rc;
+
+  rc= mysql_stmt_prepare(stmt, SL("show grants for mysqltest_8"));
+  check_stmt_rc(rc, stmt);
+
+  rc= mysql_stmt_execute(stmt);
+  check_stmt_rc(rc, stmt);
+
+  mysql_stmt_store_result(stmt);
+  FAIL_IF(!mysql_stmt_errno(stmt), "Expected error");
+  FAIL_IF(strcmp(mysql_error(mysql), mysql_stmt_error(stmt)), "Error messages differ");
+
+  mysql_stmt_close(stmt);
+
+  return OK;
+}
+
 struct my_tests_st my_tests[] = {
+  {"test_conc627", test_conc627, TEST_CONNECTION_DEFAULT, 0, NULL, NULL},
   {"test_mdev19838", test_mdev19838, TEST_CONNECTION_DEFAULT, 0, NULL, NULL},
   {"test_conc566", test_conc566, TEST_CONNECTION_DEFAULT, 0, NULL, NULL},
   {"test_conc512", test_conc512, TEST_CONNECTION_DEFAULT, 0, NULL, NULL},