有个疑问，看下面

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(gdb) r

Starting program: /home/hackyzh/Desktop/php-7.1.4/sapi/cli/php -n poc.php

[Thread debugging using libthread_db enabled]

Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".

Breakpoint 1, zif_deflate_add (execute_data=<optimized out>, 

    return_value=0x7fffffffadc0)

    at /home/hackyzh/Desktop/php-7.1.4/ext/zlib/zlib.c:1153

1153 if (in_len <= 0 && flush_type != Z_FINISH) {

(gdb) n

1157 out_size = PHP_ZLIB_BUFFER_SIZE_GUESS(in_len);

(gdb) p in_len

$1 = 4231494864

(gdb) p/x in_len

$2 = 0xfc377cd0

(gdb) n

1158 out_size = (out_size < 64) ? 64 : out_size;

(gdb) p out_size

$3 = 4294967309

(gdb) p/x out_size

$4 = 0x10000000d    

(gdb) n

1159 out = zend_string_alloc(out_size, 0);

上面的out_size按说应该溢出了啊，为啥还是这么大，难道是64位系统的缘故么。

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gdb-peda$ print l
$43 = 0x40000000            // 1024mb



5) This length "l" is then passed into zend_string_alloc as "4 * l + 2" which results in an integer overflow:

Temporary breakpoint 3, php_escape_shell_arg (str=0x7fffad000018 'A' <repeats 200 times>...) at /home/elaw/php-7.0.1/ext/standard/exec.c:348
348             cmd = zend_string_alloc(4 * l + 2, 0); /* worst case */


gdb-peda$ print 4* l + 2
$44 = 0x2 				   //Overflow


6) Stepping into zend_string_alloc to verify the integer overflow. Notice len=0x2:
zend_string_alloc (persistent=0x0, len=0x2) at /home/elaw/php-7.0.0/Zend/zend_string.h:121      
121             zend_string *ret = (zend_string *)pemalloc(ZEND_MM_ALIGNED_SIZE(_ZSTR_STRUCT_SIZE(len)), persistent);

这里他使用的也是x64系统，为啥会溢出，而我却没有，很奇怪。

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