Fix for bug #71863 Segfault when EXPLAIN with "Unknown column" error

The reason was that after the big refactoring of mysqlnd at the end of
last year code that is initializing the error_info structure in the
result set was not added. It existed already for connections and PS.
The code that segfaults is hit only with MariaDB because MariaDB sends
full metadata about the EXPLAIN query + EOF packet and only then it sends
an error packet. MySQL doesn't do that but sends directly an error which
is caught (by different code path). As errors during execution (which means
after sending meta) are pretty rare there was no test case of MySQL to
catch it.

NEWS

@@ -14,6 +14,10 @@ PHP                                                                        NEWS
   . Fixed bug #72658 (Locale::lookup() / locale_lookup() hangs if no match
     found). (Anatol)
 
+- Mysqlnd:
+  . Fixed bug #71863 (Segfault when EXPLAIN with "Unknown column" error when
+    using MariaDB). (Andrey)
+
 - Reflection:
   . Fixed bug #72661 (ReflectionType::__toString crashes with iterable).
     (Laruence)

ext/mysqli/tests/bug71863.phpt

@@ -0,0 +1,37 @@
+--TEST--
+Bug #71863 Segfault when EXPLAIN with "Unknown Column" Error
+--SKIPIF--
+<?php
+require_once('skipif.inc');
+require_once('skipifconnectfailure.inc');
+require_once("connect.inc");
+if (!$IS_MYSQLND) {
+	die("skip mysqlnd only test");
+}
+?>
+--FILE--
+<?php
+require_once("connect.inc");
+
+$req = my_mysqli_connect($host, $user, $passwd, $db, $port, $socket);
+
+// create db and table for test
+mysqli_query($req, "DROP TABLE IF EXISTS test_bug_71863") or die(mysqli_error($req));
+mysqli_query($req, "CREATE TABLE test_bug_71863 (id INT UNSIGNED NOT NULL DEFAULT 0)") or die(mysqli_error($req));
+
+// segfault if EXPLAIN + "Unknown column" error
+mysqli_query($req, "EXPLAIN SELECT `id` FROM `test_bug_71863` WHERE `owner_id` = '2' AND `object_id` = '1' AND type = '0'") or die(mysqli_error($req)."\n");
+
+?>
+--CLEAN--
+<?php
+require_once("connect.inc");
+if (!$link = my_mysqli_connect($host, $user, $passwd, $db, $port, $socket))
+    printf("[c001] [%d] %s\n", mysqli_connect_errno(), mysqli_connect_error());
+if (!mysqli_query($link, "DROP TABLE IF EXISTS test_bug_71863"))
+    printf("[c002] Cannot drop table, [%d] %s\n", mysqli_errno($link), mysqli_error($link));
+mysqli_close($link);
+?>
+--EXPECTF--
+Warning: mysqli_query(): (42S22/1054): Unknown column 'owner_id' in 'where clause' in %sbug71863.php on line %d
+Unknown column 'owner_id' in 'where clause'

ext/mysqlnd/mysqlnd_connection.c

@@ -215,11 +215,11 @@ MYSQLND_CLASS_METHODS_START(mysqlnd_connection_state)
 MYSQLND_CLASS_METHODS_END;
 
 
-/* {{{ mysqlnd_upsert_status_init */
+/* {{{ mysqlnd_connection_state_init */
 PHPAPI void
 mysqlnd_connection_state_init(struct st_mysqlnd_connection_state * const state)
 {
-	DBG_ENTER("mysqlnd_error_info_init");
+	DBG_ENTER("mysqlnd_connection_state_init");
 	state->m = &MYSQLND_CLASS_METHOD_TABLE_NAME(mysqlnd_connection_state);
 	state->state = CONN_ALLOCED;
 	DBG_VOID_RETURN;

ext/mysqlnd/mysqlnd_result.c

@@ -259,6 +259,8 @@ MYSQLND_METHOD(mysqlnd_result_buffered, free_result)(MYSQLND_RES_BUFFERED * cons
 	DBG_ENTER("mysqlnd_result_buffered::free_result");
 	DBG_INF_FMT("Freeing "MYSQLND_LLU_SPEC" row(s)", set->row_count);
 
+	mysqlnd_error_info_free_contents(&set->error_info);
+
 	if (set->type == MYSQLND_BUFFERED_TYPE_ZVAL) {
 		MYSQLND_METHOD(mysqlnd_result_buffered_zval, free_result)((MYSQLND_RES_BUFFERED_ZVAL *) set);
 	} if (set->type == MYSQLND_BUFFERED_TYPE_C) {
@@ -1954,7 +1956,6 @@ mysqlnd_result_unbuffered_init(const unsigned int field_count, const zend_bool p
 	if (!ret) {
 		DBG_RETURN(NULL);
 	}
-
 	if (!(ret->lengths = mnd_pecalloc(field_count, sizeof(size_t), persistent))) {
 		mnd_pefree(ret, persistent);
 		DBG_RETURN(NULL);
@@ -1995,6 +1996,10 @@ mysqlnd_result_buffered_zval_init(const unsigned int field_count, const zend_boo
 	if (!ret) {
 		DBG_RETURN(NULL);
 	}
+	if (FAIL == mysqlnd_error_info_init(&ret->error_info, persistent)) {
+		mnd_pefree(ret, persistent);
+		DBG_RETURN(NULL);
+	}
 	if (!(ret->lengths = mnd_pecalloc(field_count, sizeof(size_t), persistent))) {
 		mnd_pefree(ret, persistent);
 		DBG_RETURN(NULL);
@@ -2038,6 +2043,10 @@ mysqlnd_result_buffered_c_init(const unsigned int field_count, const zend_bool p
 	if (!ret) {
 		DBG_RETURN(NULL);
 	}
+	if (FAIL == mysqlnd_error_info_init(&ret->error_info, persistent)) {
+		mnd_pefree(ret, persistent);
+		DBG_RETURN(NULL);
+	}
 	if (!(ret->lengths = mnd_pecalloc(field_count, sizeof(size_t), persistent))) {
 		mnd_pefree(ret, persistent);
 		DBG_RETURN(NULL);