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

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Message-ID: <20080414165354.GF15824@duck.suse.cz>
Date:	Mon, 14 Apr 2008 18:53:54 +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 12:22:02, Lennart Sorensen wrote:
> On Mon, Apr 14, 2008 at 06:20:31PM +0200, Jan Kara wrote:
> >   Well, as Jiri Kosina wrote, this isn't a problem unless someone finds
> > a way how to use this race for some attack (and for example making f_pos
> > negative compromises security so it is not so far-fetched as it would
> > seem). So proactively fixing this makes some sence.
> 
> But you would have to be part of that process to affect the filehandle
> wouldn't you?  If you are part of the process already wouldn't it be
> easier to manipulate things directly rather than playing with the
> filehandle position?
  Well, but imagine you have a file /proc/my_secret_file from which you
are able to read from position A:a and B:b but not from position
A:b. Concievably, checks for the file position could be bypassed because of
this race... I know this is kind of dumb example but I can imagine someone
can eventually find something like this. So I guess one spin lock/unlock
pair is a price worth paying in the callpath which is quite long anyway.

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