Fix GH-16592 msg_send() crashes when the type does not serialize as expected.

It is assumed that the serialization always had initialised its buffer
zend_string, but in the case of a type not serialising, it is null.

Author: devnexen

ext/sysvmsg/sysvmsg.c

@@ -371,11 +371,15 @@ PHP_FUNCTION(msg_send)
 		php_var_serialize(&msg_var, message, &var_hash);
 		PHP_VAR_SERIALIZE_DESTROY(var_hash);
 
+		message_len = smart_str_get_len(&msg_var);
+		if (!message_len) {
+			RETURN_FALSE;
+		}
+
 		/* NB: php_msgbuf is 1 char bigger than a long, so there is no need to
 		 * allocate the extra byte. */
-		messagebuffer = safe_emalloc(ZSTR_LEN(msg_var.s), 1, sizeof(struct php_msgbuf));
-		memcpy(messagebuffer->mtext, ZSTR_VAL(msg_var.s), ZSTR_LEN(msg_var.s) + 1);
-		message_len = ZSTR_LEN(msg_var.s);
+		messagebuffer = safe_emalloc(message_len, 1, sizeof(struct php_msgbuf));
+		memcpy(messagebuffer->mtext, ZSTR_VAL(msg_var.s), message_len + 1);
 		smart_str_free(&msg_var);
 	} else {
 		char *p;

ext/sysvmsg/tests/gh16592.phpt

@@ -0,0 +1,19 @@
+--TEST--
+msg_send() segfault when the type does not serialize as expected
+--EXTENSIONS--
+sysvmsg
+--FILE--
+<?php
+class Test {
+    function __serialize() {}
+}
+
+$q = msg_get_queue(1);
+try {
+	msg_send($q, 1, new Test, true);
+} catch (\TypeError $e) {
+	echo $e->getMessage();
+}
+?>
+--EXPECT--
+Test::__serialize() must return an array