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Bug #32675 mysql_fetch_field() causes segmentation fault
Submitted: 2005-04-11 17:51 UTC Modified: 2005-04-12 08:54 UTC
From: michael at cosby dot dhs dot org Assigned:
Status: Not a bug Package: MySQL related
PHP Version: 5.0.4 OS: Linux 2.6
Private report: No CVE-ID: None
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From: michael at cosby dot dhs dot org
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 [2005-04-11 17:51 UTC] michael at cosby dot dhs dot org 
Description:
------------
environment:

apache 2.0.52 in multi-threaded mode
mysql 4.1.11 (and 4.1.6-gamma)
PHP 5.0.4

php configuration:
./configure --with-apxs2=/usr/sbin/apxs \
--with-zlib --enable-calendar \
--with-gd --with-mhash \
--with-xsl --enable-memory-limit \
--prefix=/home/php --with-mysql \
--with-openssl --with-jpeg-dir=/usr/lib \
--with-gettext \
--with-curl=/usr/local/lib

Notes:
* This bug does not occur if I use PHP 5.0.2 in the same environment instead of PHP 5.0.4. 

* It's possible that the fix for bug #31288 is related to this issue. This code does *not* call the (deprecated) function mysql_list_fields() at all.


Reproduce code:
---------------
The following code snippet (taken from WordPress wp-includes/wp-db.php, a blogging program):

while ($i < mysql_num_fields($this->result)) {                      
  $this->col_info[$i] = mysql_fetch_field($this->result);         
  $i++;                                                           
}

Even a single invocation of mysql_fetch_field() will cause the  seg. fault. Nothing is written to the server's error log from PHP itself.


Expected result:
----------------
Code inside a script should not cause a seg. fault.


Actual result:
--------------
When using the code snippet specified, the apache child running the request seg. faults.

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 [2005-04-11 17:56 UTC] sniper@php.net 
Try configure PHP using the external mysql client libraries:
1. delete config.cache file
2 run your configure with this change:
  --with-mysql=/usr (or whatever the install PREFIX is)

Also note: /usr/local/lib or /usr/lib are NOT correct values for any PHP configure option!! They're /usr/local and /usr
 [2005-04-11 19:54 UTC] georg@php.net 
Does the problem still exist if you disable MySQL's query cache?
 [2005-04-11 20:01 UTC] michael at cosby dot dhs dot org 
It looks like my query cache is already disabled:

mysql> show variables;
+---------------------------------+----------------------------+
| Variable_name                   | Value                      |
+---------------------------------+----------------------------+
...
| query_cache_limit               | 1048576                    |
| query_cache_min_res_unit        | 4096                       |
| query_cache_size                | 0                          |
| query_cache_type                | ON                         |
| query_cache_wlock_invalidate    | OFF                        |
...


From the mysql manual at http://dev.mysql.com/doc/mysql/en/query-cache.html:

"
To disable the query cache at server startup, set the query_cache_size system variable to 0. By disabling the query cache code, there is no noticeable overhead.
"

(I'm not real familiar with the query cache, so I wanted to be 100% sure it was disabled).
 [2005-04-11 20:04 UTC] michael at cosby dot dhs dot org 
For the libraries, it appears that my PHP is *not* compiling with the 4.1.11 client library, but with a 4.0.21 client library. I'm trying to get it to compile with with the 4.1.11 library to see what happens, but I doubt that will fix it since this same 4.0.21 client library works fine with PHP 5.0.2.
 [2005-04-11 22:24 UTC] michael at cosby dot dhs dot org 
It appears that I'm already using the external mysql client library, or I'm reading phpinfo() wrong:

MySQL Support	enabled
Active Persistent Links 	0
Active Links 	0
Client API version 	4.0.21
MYSQL_MODULE_TYPE 	external
MYSQL_SOCKET 	/tmp/mysql.sock
MYSQL_INCLUDE 	-I/usr/include/mysql
MYSQL_LIBS 	-L/usr/lib -lmysqlclient
 [2005-04-11 23:13 UTC] sniper@php.net 
Noticed this: "apache 2.0.52 in multi-threaded mode"..
What if you try with prefork apache2?
 [2005-04-12 08:43 UTC] michael at cosby dot dhs dot org 
Well, that's embarrasing... I was compiling with the mysql 4.1 include files but the 4.0.21 binaries, so of course my pre-compiled 5.0.2 kept working.....
 [2005-04-12 08:54 UTC] tony2001@php.net 
No PHP bug -> bogus.
 
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