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

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Message-ID: <20080414183434.GB5234@martell.zuzino.mipt.ru>
Date:	Mon, 14 Apr 2008 22:34:34 +0400
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Jan Kara <jack@...e.cz>,
	Lennart Sorensen <lsorense@...lub.uwaterloo.ca>,
	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, Apr 14, 2008 at 05:54:52PM +0100, Alan Cox wrote:
> >   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
> 
> Unlikely as the ppos passed to the driver is a private copy and the user
> could equally use pread/pwrite to specify that offset.

pread is banned on proc files implemented via seq_files.
And in no-seq_file case, there are MAX_NON_LFS checks which fits into
32 bits.

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