full-disclosure - Re: {Java,PHP} Server Exploits

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Date: Wed, 09 Feb 2011 15:13:11 -0500
From: Valdis.Kletnieks@...edu
To: Christian Sciberras <uuf6429@...il.com>
Cc: full-disclosure@...ts.grok.org.uk, literalka@...a.eu
Subject: Re: {Java,PHP} Server Exploits

On Wed, 09 Feb 2011 20:54:41 +0100, Christian Sciberras said:

>     $f=floatval("2.2250738585072011e-308");
>     echo 'Try 2 => '.$f.'</br>';

> Plus, I'm a bit amazed such a bug exists in PHP - since converting to
> floating point is a trivial operation, it should have been limited and
> safe-guarded from the start.

Take a careful gander at that number, then go look at the floating point spec -
it's a specific corner case that isn't obviously trivial to get right (doing
floating point *right* is a lot harder than it looks - take a class on
numerical methods sometime, you spend 75% of your time dealing with rounding
errors in the last bit).

Having said that, anybody writing floating point support for a package should
probably google 'floating point paranoia' and learn what sort of things to test
for. :)

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