linux-kernel - Re: [PATCH 1/1] FS/OMFS: block number sanity check during fill

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Date:	Thu, 26 Jun 2014 20:44:03 +0200
From:	Fabian Frederick <fabf@...net.be>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Bob Copeland <me@...copeland.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/1] FS/OMFS: block number sanity check during
 fill_super operation

On Thu, 26 Jun 2014 11:35:57 -0700
Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> On Jun 26, 2014 11:28 AM, "Fabian Frederick" <fabf@...net.be> wrote:
> >
> >    Sorry but I don't see a problem with 2^31 value.
> 
> It's not really 2^31.
> 
> It's *negative* 2^31.
> 
> 1 is "int", so it's a signed number. With the shift it ends up being a
> signed number with the high bit set. That's just a bad bad idea.
> 
> Now, it just so happens that if you always compare it with unsigned
> numbers, C promotion rules will end up promoting it to unsigned and it
> happens to *work*, but that is more luck than design.
> 
> So I'd suggest using 0x80000000 (which is unsigned) or use (1ul<<31) or
> similar explicit C typing.

Ok, I understand now. Thanks a lot for taking the time to explain Linus.
It really means a lot to me.

Fabian
> 
>      Linus
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