Description:
------------
Argument stack reallocations may cause heap corruption or segmentation faults.

Functions that accept arguments through zend_get_parameters (zval ** - pointer to zend_ptr_stack element) and running user callbacks that may need more stack space are affected.

So unserialize (__wakeup), sort functions in 4.4 version, and so on.

Also using complicated user error handler is quite risky.

Reproduce code:
---------------
<?
class test {
        function extend_zend_ptr_stack($count,$a,$b,$c,$d,$e) {
                if ($count>0) $this->extend_zend_ptr_stack($count - 1,$a,$b,$c,$d,$e);
        }

        function __wakeup() {
                $this->extend_zend_ptr_stack(10,'a','b','c','d','e');
        }
}

$str='a:2:{i:0;O:4:"test":0:{}junk';
var_dump(unserialize($str));


Expected result:
----------------
bool(false)


Actual result:
--------------
#0  0x081be837 in zif_unserialize (ht=1, return_value=0x9b97ddc, return_value_ptr=0x0, this_ptr=0x0, return_value_used=1) at /root/cvs/php_5_1/ext/standard/var.c:860
#1  0x08234f10 in zend_do_fcall_common_helper_SPEC (execute_data=0xbfec6c80) at /root/cvs/php_5_1/Zend/zend_vm_execute.h:192
#2  0x082348a1 in execute (op_array=0x9ba611c) at /root/cvs/php_5_1/Zend/zend_vm_execute.h:92
#3  0x0821acb2 in zend_execute_scripts (type=8, retval=0x0, file_count=3) at /root/cvs/php_5_1/Zend/zend.c:1101
#4  0x081e2804 in php_execute_script (primary_file=0xbfec9180) at /root/cvs/php_5_1/main/main.c:1719
#5  0x08285f9e in main (argc=2, argv=0xbfec9254) at /root/cvs/php_5_1/sapi/cli/php_cli.c:1090