Fix bug #72413: Segfault with get_result and PS cursors

We cannot simply switch to use_result here, because the fetch_row
methods in get_result mode and in use_result/store_result mode
are different: In one case it accepts a statement, in the other
a return value zval. Thus, doing a switch to use_result results
in a segfault when trying to fetch a row.

Actually supporting get_result with cursors would require adding
cursor support in mysqlnd_result, not just mysqlnd_ps. That would
be a significant amount of effort and, given the age of the issue,
does not appear to be particularly likely to happen soon.

As such, we simply generate an error when using get_result()
with cursors, which is much better than causing a segfault.
Instead, parameter binding needs to be used.

NEWS

@@ -31,6 +31,8 @@ PHP                                                                        NEWS
     timeout). (Kamil Tekiela, Nikita)
   . Fixed bug #76525 (mysqli::commit does not throw if MYSQLI_REPORT_ERROR
     enabled and mysqlnd used). (Kamil Tekiela)
+  . Fixed bug #72413 (mysqlnd segfault (fetch_row second parameter
+    typemismatch)). (Kamil Tekiela)
 
 - ODBC:
   . Fixed bug #44618 (Fetching may rely on uninitialized data). (cmb)

ext/mysqli/tests/mysqli_stmt_get_result.phpt

@@ -124,32 +124,77 @@ if (!function_exists('mysqli_stmt_get_result'))
 	if (true !== ($tmp = mysqli_stmt_bind_result($stmt, $id, $label)))
 		printf("[035] Expecting boolean/true, got %s/%s\n", gettype($tmp), var_export($tmp, 1));
 
-	if (!is_object($tmp = $result = mysqli_stmt_get_result($stmt)))
-		printf("[036] Expecting array, got %s/%s, [%d] %s\n",
-			gettype($tmp), var_export($tmp, 1),
-			mysqli_stmt_errno($stmt), mysqli_stmt_error($stmt));
-
-	if (false !== ($tmp = mysqli_stmt_fetch($stmt)))
-		printf("[037] Expecting boolean/false, got %s/%s, [%d] %s\n",
-			gettype($tmp), $tmp, mysqli_stmt_errno($stmt), mysqli_stmt_error($stmt));
-
-	printf("[038] [%d] [%s]\n", mysqli_stmt_errno($stmt), mysqli_stmt_error($stmt));
-	printf("[039] [%d] [%s]\n", mysqli_errno($link), mysqli_error($link));
-	while ($row = mysqli_fetch_assoc($result)) {
-		var_dump($row);
-	}
-	mysqli_free_result($result);
+    // get_result cannot be used in PS cursor mode
+    if (!$stmt = mysqli_stmt_init($link))
+        printf("[030] [%d] %s\n", mysqli_errno($link), mysqli_error($link));
+
+    if (!mysqli_stmt_prepare($stmt, "SELECT id, label FROM test ORDER BY id LIMIT 2"))
+        printf("[031] [%d] %s\n", mysqli_stmt_errno($stmt), mysqli_stmt_error($stmt));
+
+    if (!mysqli_stmt_attr_set($stmt, MYSQLI_STMT_ATTR_CURSOR_TYPE, MYSQLI_CURSOR_TYPE_READ_ONLY))
+        printf("[032] [%d] %s\n", mysqli_stmt_errno($stmt), mysqli_stmt_error($stmt));
+
+    if (!mysqli_stmt_execute($stmt))
+        printf("[033] [%d] %s\n", mysqli_stmt_errno($stmt), mysqli_stmt_error($stmt));
+
+    mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);
+    try {
+        $res = mysqli_stmt_get_result($stmt);
+        // we expect no segfault if we try to fetch a row because get_result should throw an error or return false
+        mysqli_fetch_assoc($res);
+    } catch (\mysqli_sql_exception $e) {
+        echo $e->getMessage() . "\n";
+    }
+
+    try {
+        $res = $stmt->get_result();
+        // we expect no segfault if we try to fetch a row because get_result should throw an error or return false
+        $res->fetch_assoc();
+    } catch (\mysqli_sql_exception $e) {
+        echo $e->getMessage() . "\n";
+    }
+    mysqli_report(MYSQLI_REPORT_OFF);
+
+    if (!$stmt = mysqli_stmt_init($link))
+        printf("[034] [%d] %s\n", mysqli_errno($link), mysqli_error($link));
+
+    if (!mysqli_stmt_prepare($stmt, "SELECT id, label FROM test ORDER BY id LIMIT 2"))
+        printf("[035] [%d] %s\n", mysqli_stmt_errno($stmt), mysqli_stmt_error($stmt));
+
+    if (!mysqli_stmt_execute($stmt))
+        printf("[036] [%d] %s\n", mysqli_stmt_errno($stmt), mysqli_stmt_error($stmt));
+
+    $id = NULL;
+    $label = NULL;
+    if (true !== ($tmp = mysqli_stmt_bind_result($stmt, $id, $label)))
+        printf("[037] Expecting boolean/true, got %s/%s\n", gettype($tmp), var_export($tmp, 1));
+
+    if (!is_object($tmp = $result = mysqli_stmt_get_result($stmt)))
+        printf("[038] Expecting array, got %s/%s, [%d] %s\n",
+            gettype($tmp), var_export($tmp, 1),
+            mysqli_stmt_errno($stmt), mysqli_stmt_error($stmt));
+
+    if (false !== ($tmp = mysqli_stmt_fetch($stmt)))
+        printf("[039] Expecting boolean/false, got %s/%s, [%d] %s\n",
+            gettype($tmp), $tmp, mysqli_stmt_errno($stmt), mysqli_stmt_error($stmt));
+
+    printf("[040] [%d] [%s]\n", mysqli_stmt_errno($stmt), mysqli_stmt_error($stmt));
+    printf("[041] [%d] [%s]\n", mysqli_errno($link), mysqli_error($link));
+    while ($row = mysqli_fetch_assoc($result)) {
+        var_dump($row);
+    }
+    mysqli_free_result($result);
 
 	if (!mysqli_kill($link, mysqli_thread_id($link)))
-		printf("[040] [%d] %s\n", mysqli_errno($link), mysqli_error($link));
+		printf("[042] [%d] %s\n", mysqli_errno($link), mysqli_error($link));
 
 	if (false !== ($tmp = mysqli_stmt_get_result($stmt)))
-		printf("[041] Expecting false, got %s/%s\n", gettype($tmp), var_export($tmp, 1));
+		printf("[043] Expecting false, got %s/%s\n", gettype($tmp), var_export($tmp, 1));
 
 	mysqli_stmt_close($stmt);
 
 	if (false !== ($tmp = mysqli_stmt_fetch($stmt)))
-		printf("[042] Expecting false, got %s/%s\n", gettype($tmp), var_export($tmp, 1));
+		printf("[044] Expecting false, got %s/%s\n", gettype($tmp), var_export($tmp, 1));
 
 	mysqli_close($link);
 
@@ -168,8 +213,10 @@ Warning: mysqli_stmt_fetch(): invalid object or resource mysqli_stmt
 
 Warning: mysqli_stmt_get_result(): invalid object or resource mysqli_stmt
  in %s on line %d
-[038] [2014] [Commands out of sync; you can't run this command now]
-[039] [0] []
+mysqli_stmt_get_result() cannot be used with cursors
+get_result() cannot be used with cursors
+[040] [2014] [Commands out of sync; you can't run this command now]
+[041] [0] []
 array(2) {
   ["id"]=>
   int(1)

ext/mysqlnd/mysqlnd_ps.c

@@ -153,13 +153,19 @@ MYSQLND_METHOD(mysqlnd_stmt, get_result)(MYSQLND_STMT * const s)
 	}
 
 	if (stmt->cursor_exists) {
-		/* Silently convert buffered to unbuffered, for now */
-		DBG_RETURN(s->m->use_result(s));
+		/* Prepared statement cursors are not supported as of yet */
+		char * msg;
+		mnd_sprintf(&msg, 0, "%s() cannot be used with cursors", get_active_function_name());
+		SET_CLIENT_ERROR(stmt->error_info, CR_NOT_IMPLEMENTED, UNKNOWN_SQLSTATE, msg);
+		if (msg) {
+			mnd_sprintf_free(msg);
+		}
+		DBG_RETURN(NULL);
 	}
 
 	/* Nothing to store for UPSERT/LOAD DATA*/
 	if (GET_CONNECTION_STATE(&conn->state) != CONN_FETCHING_DATA || stmt->state != MYSQLND_STMT_WAITING_USE_OR_STORE) {
-		SET_CLIENT_ERROR(conn->error_info, CR_COMMANDS_OUT_OF_SYNC, UNKNOWN_SQLSTATE, mysqlnd_out_of_sync);
+		SET_CLIENT_ERROR(stmt->error_info, CR_COMMANDS_OUT_OF_SYNC, UNKNOWN_SQLSTATE, mysqlnd_out_of_sync);
 		DBG_RETURN(NULL);
 	}