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Date: Fri, 17 Mar 2006 07:00:59 -0500
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To: Dmitry Stogov <dmitry@zend.com>
CC: Wez Furlong <kingwez@gmail.com>, internals@lists.php.net
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Subject: Re: [PHP-DEV] Problem with ext/libxml RINIT/RSHUTDOWN
From: rrichards@ctindustries.net (Rob Richards)

Dmitry Stogov wrote:
> Hi Wez,
>
> I found a bad code in ext/libxml.
>
> On each request startup/shutdown it changing some libxml callbacks.
> At first this slowdown each request, at second multi-threaded PHP may fail,
> because different threads may set/clean the same callbacks in the same time.
>
> May be it is possible to setup these callbacks forever in MINIT/MSHUTDOWN,
> set some flag (somthing like LIBXML(in_request)) in RINIT/RSHUTDOWN, and
> check it in callbacks.
>   
Which ones in particular?
Each of the callbacks being utilized are thread safe.
The reason why they need to be set per request is in order to play nice 
with any other modules that might be loaded and use libxml2.

for example: prior to how the current callbacks are implemented it was 
possible to blow away PHP stream usage by any of the xml extensions 
using mod_perl and its xsl module (could do this whether or not PHP was 
running threaded).
There are also many other ways to screw with the libxml2 globals and 
effect PHP extensions based on libxml2 as well using other modules so 
the only way to protect them is on each request. In short putting them 
into the MINIT/MSHUTDOWN will open security holes.

Rob