Fix bug #77371 (heap buffer overflow in mb regex functions - compile_string_node)

ext/mbstring/oniguruma/regcomp.c

@@ -524,6 +524,7 @@ compile_string_node(Node* node, regex_t* reg)
 
   for (; p < end; ) {
     len = enclen(enc, p);
+    if (p + len > end) len = end - p;
     if (len == prev_len) {
       slen++;
     }

ext/mbstring/tests/bug77371.phpt

@@ -0,0 +1,10 @@
+--TEST--
+Bug #77371 (heap buffer overflow in mb regex functions - compile_string_node)
+--SKIPIF--
+<?php extension_loaded('mbstring') or die('skip mbstring not available'); ?>
+--FILE--
+<?php
+var_dump(mb_ereg("()0\xfc00000\xfc00000\xfc00000\xfc",""))
+?>
+--EXPECT--
+bool(false)