full-disclosure - Re: Firefox 2.0.0.7 has a very serious calculation bug [FIB FOUND/CONFIRMED]

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Date: Fri, 28 Sep 2007 23:28:32 +0530
From: "Susam Pal" <susam.pal@...il.com>
To: blah <blah@...kogre.com>
Cc: full-disclosure@...ts.grok.org.uk, carl hardwick <hardwick.carl@...il.com>,
	Larry Seltzer <Larry@...ryseltzer.com>
Subject: Re: Firefox 2.0.0.7 has a very serious
	calculation bug [FIB FOUND/CONFIRMED]

Compile and run this.

#include <stdio.h>

int main(int argc, char **argv) {
  float a = 0.7;
  if(a == 0.7) {
    printf("%f is equal to %f\n", a, 0.7);
  } else {
    printf("%f is not equal to %f\n", a, 0.7);
  }
}

On many implementations (not necessarily all implementations) you will
get the output as:-

0.700000 is not equal to 0.700000

For example, on my Debian Etch with gcc 4.1.2, the output is as shown
above. This doesn't mean it is a bug in 'gcc'. It's just a limitation
of floating point math. If someone doesn't take care of the floating
point behavior while writing code in JavaScript, it is a bug in the
JavaScript code and not a bug in Firefox.

Regards,
Susam Pal
http://susam.in/

On 9/28/07, blah <blah@...kogre.com> wrote:
> IE7 was fine for me, showed up in FF 2.0.0.7
>
> However, I think it's much wider-spread than initially thought.  I
> found the same most unsettling results using:
> javascript:4.2-0.1
> javascript:3.2-0.1
> javascript:2.2-0.1
>
> I did not have time to try more, but obviously all of you can see the
> possibilities.  Because it appears this works with any number, I've
> dubbed it the FIB, (Firefox Infinite Bug).
>
> I think this should get its own exploit category, too, since
> assuredly, perhaps one day, this will be exploitable.
>
> On 9/28/07, Steven Adair <steven@...urityzone.org> wrote:
> > So are we dealing with an RDCB (Recently Disclosed Calculation Bug) or was
> > this just a mistake?
> >
> > Steven
> >
> > > Actually, I see 5.1000000000000005 in both browsers.
> > >
> > > Larry Seltzer
> > > eWEEK.com Security Center Editor
>
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