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Bug #72040 AddressSanitizer: heap-use-after-free zend_alloc.c:924 zend_mm_del_segment
Submitted: 2016-04-17 06:53 UTC Modified: 2016-07-14 09:32 UTC
From: fernando at null-life dot com Assigned: dmitry (profile)
Status: Closed Package: Reproducible crash
PHP Version: 5.6.20 OS: Linux
Private report: No CVE-ID: None
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 [2016-04-17 06:53 UTC] fernando at null-life dot com 
Description:
------------
1. compile PHP 5.6.20 with ASAN
2. Run attached script on a while loop, sometimes you will get the ASAN crash.

  while true; do /home/fmunozs/phpgit/php56/sapi/cli/php -n jet.php ; done

if php_request_shutdown is called during the fscanf, ASAN reports a heap-use-after-free in some cases.

Test script:
---------------
<?php

set_time_limit(1);
$arr = []; for($i=0;$i<165536; ++$i) { $arr[$i]= "aa"; }
$var1=fopen("/dev/zero", "r");
$var2="AAA";
try{fscanf($var1, $var2);}catch(Exception $a) {}

Expected result:
----------------
No warning

Actual result:
--------------
Fatal error: Maximum execution time of 1 second exceeded in /ramdisk/wtf/wtf/jet.php on line 7
=================================================================
==29856==ERROR: AddressSanitizer: heap-use-after-free on address 0xac533804 at pc 0x0930ffba bp 0xbfdf0358 sp 0xbfdf0348
READ of size 4 at 0xac533804 thread T0
    #0 0x930ffb9 in zend_mm_del_segment /home/fmunozs/phpgit/php56/Zend/zend_alloc.c:924
    #1 0x930ffb9 in _zend_mm_free_int /home/fmunozs/phpgit/php56/Zend/zend_alloc.c:2115
    #2 0x930ffb9 in _efree /home/fmunozs/phpgit/php56/Zend/zend_alloc.c:2440
    #3 0x94d1d4f in zend_hash_destroy /home/fmunozs/phpgit/php56/Zend/zend_hash.c:553
    #4 0x94612d1 in _zval_dtor_func /home/fmunozs/phpgit/php56/Zend/zend_variables.c:45
    #5 0x93d83e8 in _zval_dtor /home/fmunozs/phpgit/php56/Zend/zend_variables.h:35
    #6 0x93d83e8 in i_zval_ptr_dtor /home/fmunozs/phpgit/php56/Zend/zend_execute.h:79
    #7 0x93d83e8 in _zval_ptr_dtor /home/fmunozs/phpgit/php56/Zend/zend_execute_API.c:424
    #8 0x94d3f53 in i_zend_hash_bucket_delete /home/fmunozs/phpgit/php56/Zend/zend_hash.c:182
    #9 0x94d3f53 in zend_hash_bucket_delete /home/fmunozs/phpgit/php56/Zend/zend_hash.c:192
    #10 0x94d3f53 in zend_hash_graceful_reverse_destroy /home/fmunozs/phpgit/php56/Zend/zend_hash.c:613
    #11 0x93daf4d in shutdown_executor /home/fmunozs/phpgit/php56/Zend/zend_execute_API.c:244
    #12 0x9467c8b in zend_deactivate /home/fmunozs/phpgit/php56/Zend/zend.c:960
    #13 0x91a88d0 in php_request_shutdown /home/fmunozs/phpgit/php56/main/main.c:1899
    #14 0x9a83ac3 in do_cli /home/fmunozs/phpgit/php56/sapi/cli/php_cli.c:1177
    #15 0x808a502 in main /home/fmunozs/phpgit/php56/sapi/cli/php_cli.c:1378
    #16 0xb6dcd645 in __libc_start_main (/lib/i386-linux-gnu/libc.so.6+0x18645)
    #17 0x808aaba  (/home/fmunozs/phpgit/php56/sapi/cli/php+0x808aaba)

0xac533804 is located 4 bytes inside of 13369344-byte region [0xac533800,0xad1f3800)
freed by thread T0 here:
    #0 0xb727f06c in __interceptor_realloc (/usr/lib/i386-linux-gnu/libasan.so.2+0x9706c)
    #1 0x92e89cb in zend_mm_mem_malloc_realloc /home/fmunozs/phpgit/php56/Zend/zend_alloc.c:292

previously allocated by thread T0 here:
    #0 0xb727f06c in __interceptor_realloc (/usr/lib/i386-linux-gnu/libasan.so.2+0x9706c)
    #1 0x92e89cb in zend_mm_mem_malloc_realloc /home/fmunozs/phpgit/php56/Zend/zend_alloc.c:292

SUMMARY: AddressSanitizer: heap-use-after-free /home/fmunozs/phpgit/php56/Zend/zend_alloc.c:924 zend_mm_del_segment
Shadow bytes around the buggy address:
  0x358a66b0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x358a66c0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x358a66d0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x358a66e0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x358a66f0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
=>0x358a6700:[fd]fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
  0x358a6710: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
  0x358a6720: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
  0x358a6730: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
  0x358a6740: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
  0x358a6750: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07 
  Heap left redzone:       fa
  Heap right redzone:      fb
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack partial redzone:   f4
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Container overflow:      fc
  Array cookie:            ac
  Intra object redzone:    bb
  ASan internal:           fe
==29856==ABORTING

Patches

Pull Requests

History

AllCommentsChangesGit/SVN commitsRelated reports
 [2016-04-18 00:31 UTC] stas@php.net
-Type: Security +Type: Bug
 [2016-04-18 00:31 UTC] stas@php.net 
Does not look like a security issue - specially crafted code that also makes little sense.
 [2016-04-19 01:45 UTC] fernando at null-life dot com 
I can't ask my fuzzer to make sense :) but please take a look, it keeps appearing on my fuzzing session, seems to happen also if the shutdown occurs during fgetcsv call too.
 [2016-04-19 09:46 UTC] dmitry@php.net 
PHP doesn't handle execution time-out gracefully.
In some cases it may cause crash on request shutdown.

exit_on_timeout=1 in php.ini should minimize the risk.

The only way to fix this properly - is delaying the actual signal handling until the safe place. E.g like PHP on Windows do, setting EG(timed_out) in signal handler, and checking it from time to time in interpreter. However, this approach won't interrupt long running internal functions.
 [2016-07-14 09:32 UTC] dmitry@php.net
-Status: Open +Status: Closed -Assigned To: +Assigned To: dmitry
 [2016-07-14 09:32 UTC] dmitry@php.net 
Graceful execution time-out handling is implemented in PHP-7.1.
 
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