Date: Tue, 7 Sep 2004 02:59:21 -0700
From: Andrew Morton <akpm@osdl.org>
To: Jens Axboe <axboe@suse.de>
Cc: paulus@samba.org, juhl-lkml@dif.dk, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] remember to check return value from __copy_to_user() in
 cdrom_read_cdda_old()
Message-Id: <20040907025921.7f6a4139.akpm@osdl.org>
In-Reply-To: <20040907093437.GK6323@suse.de>
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Jens Axboe <axboe@suse.de> wrote:
>
> On Tue, Sep 07 2004, Paul Mackerras wrote:
> > Jens Axboe writes:
> > 
> > > __copy_to_user is the unchecking version of copy_to_user.
> > 
> > It doesn't range-check the address, but it does return non-zero
> > (number of bytes not copied) if it encounters a fault writing to the
> > user buffer.
> 
> but it doesn't matter, if it returns non-zero then something happened
> between the access_ok() and the actual copy because the user app did
> something silly. so I don't care much really, I think the major point is
> the kernel will cope.
> 
> you could remove the access_ok() and change it to a copy_to_user()
> instead, I don't care either way. it's the old and slow interface which
> really never is used unless things have gone wrong anyways.
> 

Sure, but at present if an application tries to read cdrom data to address
0x00000000 (say), the kernel will return "success".  It should return an
error code.  (Actually, it should return a short read if any data was
transferred, but whatever).

Plus the patch will fix a __must_check warning.
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