linux-kernel - Re: file offset corruption on 32-bit machines?

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Message-ID: <20080414194246.GN15824@duck.suse.cz>
Date:	Mon, 14 Apr 2008 21:42:46 +0200
From:	Jan Kara <jack@...e.cz>
To:	Lennart Sorensen <lsorense@...lub.uwaterloo.ca>
Cc:	Bodo Eggert <7eggert@....de>, Diego Calleja <diegocg@...il.com>,
	Jiri Kosina <jkosina@...e.cz>, Michal Hocko <mhocko@...e.cz>,
	Meelis Roos <mroos@...ux.ee>,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org
Subject: Re: file offset corruption on 32-bit machines?

On Mon 14-04-08 15:29:28, Lennart Sorensen wrote:
> On Mon, Apr 14, 2008 at 09:03:09PM +0200, Jan Kara wrote:
> >   Why would it be doing locking? If some nasty user runs the process, he
> > *wants* his two threads to race as much as possible and trigger the race.
> > And then use corrupted f_pos.
> 
> Why would you want to?  You can already set the filepointer explicitly
> to any value you want if you have the filehandle.
> 
> If you had a file with some security checks for whether the user could
> read from it implemented based on locations then you would check it when
> you read/write not when you seek, since after all you could just keep
> reading until you get to the desired position.
  Yes and no - for example if you manage to corrupt f_pos so that it
becomes negative, you have won because it is checked only in seek, pread,
pwrite, but not in read or write which rely on the check in seek...

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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