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Bug #43229 array_walk() crashes with a segmentation fault
Submitted: 2007-11-09 20:45 UTC Modified: 2008-08-06 03:55 UTC
Votes:5
Avg. Score:4.2 ± 0.7
Reproduced:5 of 5 (100.0%)
Same Version:2 (40.0%)
Same OS:3 (60.0%)
From: tobsn@php.net Assigned: dmitry (profile)
Status: Wont fix Package: Scripting Engine problem
PHP Version: 5.2CVS-2008-03-25 (CVS) OS: CentOS
Private report: No CVE-ID: None
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 [2007-11-09 20:45 UTC] tobsn@php.net 
Description:
------------
strace doesnt output anything - it just cuts the output with a segfault.

if you change the variable from $thiskeyword to something else without "this" at the start, it works correctly... ;)

Reproduce code:
---------------
<?php

$stopwords = array( 'this', 'a', 'the', 'is' );
$keyword = explode( ' ', 'this is a big problem' );

for( $i = 0; $i < 1000; $i++ ) {
        $thiskeyword = $keyword;
        array_walk( $thiskeyword, create_function('$v,$k','global $thiskeyword,$stopwords;if(in_array($v,$stopwords)){unset($thiskeyword[$k]);}'));
}

?>

Actual result:
--------------
Segmentation Fault

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AllCommentsChangesGit/SVN commitsRelated reports
 [2007-11-09 23:07 UTC] stas@php.net 
Looks like a problem happens because array is modified while array_walk is walking it.
 [2007-11-10 00:05 UTC] tobsn@php.net 
if you use a different var name like $tmpkeyword instead of $thiskeyword - it works... ;)
 [2007-11-12 11:58 UTC] jani@php.net 
I get the same crash regardless what the variable name is:

Program received signal SIGSEGV, Segmentation fault.
0x08305dea in zend_hash_get_current_data_ex (ht=0x928721c, pData=0xbff8e0fc, pos=0xbff8e0e4) at /home/jani/src/php-5.3/Zend/zend_hash.c:1163
1163                    *pData = p->pData;
(gdb) bt
#0  0x08305dea in zend_hash_get_current_data_ex (ht=0x928721c, pData=0xbff8e0fc, pos=0xbff8e0e4) at /home/jani/src/php-5.3/Zend/zend_hash.c:1163
#1  0x082015df in php_array_walk (target_hash=0x928721c, userdata=0x0, recursive=0) at /home/jani/src/php-5.3/ext/standard/array.c:1035
#2  0x08201834 in zif_array_walk (ht=2, return_value=0x9287a18, return_value_ptr=0x0, this_ptr=0x0, return_value_used=0)
    at /home/jani/src/php-5.3/ext/standard/array.c:1126
#3  0x0831f002 in zend_do_fcall_common_helper_SPEC (execute_data=0xbff8e3bc) at /home/jani/src/php-5.3/Zend/zend_vm_execute.h:194
#4  0x08324824 in ZEND_DO_FCALL_SPEC_CONST_HANDLER (execute_data=0xbff8e3bc) at /home/jani/src/php-5.3/Zend/zend_vm_execute.h:1439
#5  0x0831eb06 in execute (op_array=0x9285f10) at /home/jani/src/php-5.3/Zend/zend_vm_execute.h:87
#6  0x082f7a7e in zend_execute_scripts (type=8, retval=0x0, file_count=3) at /home/jani/src/php-5.3/Zend/zend.c:1139
#7  0x0829ff95 in php_execute_script (primary_file=0xbff90740) at /home/jani/src/php-5.3/main/main.c:2007
#8  0x0837f5c4 in main (argc=2, argv=0xbff90894) at /home/jani/src/php-5.3/sapi/cli/php_cli.c:1140
 [2007-12-03 15:13 UTC] david at grant dot org dot uk 
Reproduced on PHP 5.2.5 on RHEL 4.

#0  zend_call_function (fci=0xbff5f4e0, fci_cache=0xbff5f510) at /home/wdierkes/buildroot/BUILD/php-5.2.5/Zend/zend_execute_API.c:911
#1  0x0309aa8b in php_array_walk (target_hash=0xb7aa1208, userdata=0xbff5f578, recursive=0) at /home/wdierkes/buildroot/BUILD/php-5.2.5/ext/standard/array.c:1114
#2  0x0309ae64 in zif_array_walk (ht=3, return_value=0xb7ab3a78, return_value_ptr=0x0, this_ptr=0x0, return_value_used=0)
    at /home/wdierkes/buildroot/BUILD/php-5.2.5/ext/standard/array.c:1171
#3  0x0318a244 in zend_do_fcall_common_helper_SPEC (execute_data=0xbff5f7f0) at /home/wdierkes/buildroot/BUILD/php-5.2.5/Zend/zend_vm_execute.h:200
#4  0x0318971a in execute (op_array=0xb7b8d50c) at /home/wdierkes/buildroot/BUILD/php-5.2.5/Zend/zend_vm_execute.h:92
#5  0x03189a1f in zend_do_fcall_common_helper_SPEC (execute_data=0xbff5ffc0) at /home/wdierkes/buildroot/BUILD/php-5.2.5/Zend/zend_vm_execute.h:234
#6  0x0318971a in execute (op_array=0xb7b8cd50) at /home/wdierkes/buildroot/BUILD/php-5.2.5/Zend/zend_vm_execute.h:92
#7  0x03189a1f in zend_do_fcall_common_helper_SPEC (execute_data=0xbff602f0) at /home/wdierkes/buildroot/BUILD/php-5.2.5/Zend/zend_vm_execute.h:234
#8  0x0318971a in execute (op_array=0xb7b891f8) at /home/wdierkes/buildroot/BUILD/php-5.2.5/Zend/zend_vm_execute.h:92
#9  0x03189a1f in zend_do_fcall_common_helper_SPEC (execute_data=0xbff60650) at /home/wdierkes/buildroot/BUILD/php-5.2.5/Zend/zend_vm_execute.h:234
#10 0x0318971a in execute (op_array=0xb7b37e24) at /home/wdierkes/buildroot/BUILD/php-5.2.5/Zend/zend_vm_execute.h:92
#11 0x03189a1f in zend_do_fcall_common_helper_SPEC (execute_data=0xbff625f0) at /home/wdierkes/buildroot/BUILD/php-5.2.5/Zend/zend_vm_execute.h:234
#12 0x0318971a in execute (op_array=0xb7cd7930) at /home/wdierkes/buildroot/BUILD/php-5.2.5/Zend/zend_vm_execute.h:92
#13 0x03168d4b in zend_execute_scripts (type=8, retval=0x1a4, file_count=3) at /home/wdierkes/buildroot/BUILD/php-5.2.5/Zend/zend.c:1134
#14 0x031214fb in php_execute_script (primary_file=0xbff648e0) at /home/wdierkes/buildroot/BUILD/php-5.2.5/main/main.c:2004
#15 0x0320caee in php_handler (r=0x96a8480) at /home/wdierkes/buildroot/BUILD/php-5.2.5/sapi/apache2handler/sapi_apache2.c:631
 [2008-01-22 13:45 UTC] felipe@php.net 
Works fine to me. 
PHP 5.3.0-dev (cli) (built: Jan 18 2008 12:20:16)
 [2008-02-09 01:10 UTC] stas@php.net 
Still creashes for me in 5.3CVS. Please do not re-close without ensuring a fix - UMRs or memory corruption can be elusive and not show on some environments while existing on others.
 [2008-03-25 13:52 UTC] jani@php.net 
Still crashes using latest 5.2 snapshot.
 [2008-04-12 14:54 UTC] jani@php.net 
Dmitry, can you please check this out? It's pretty bad if just a certain name of variable causes a crash.
 [2008-04-14 11:23 UTC] dmitry@php.net 
The crash is not related to variable name. It occurs because the script unset()s the element of array which is still referenced from the array_walk() function. So later array_walk() tries to access freed memory and may crash.

The array_walk() manual says:
Users may not change the array  itself from the callback function. e.g. Add/delete elements, unset elements, etc. If the array that array_walk() is applied to is changed, the behavior of this function is undefined, and unpredictable.

I think this bug shouldn't be fixed.
 
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