linux-kernel - Re: [PATCH 49/61] ISDN: fix drivers, by handling errors thrown by ->readstat()

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Date:	Wed, 1 Nov 2006 10:18:22 +0100
From:	Karsten Keil <kkeil@...e.de>
To:	Willy Tarreau <w@....eu>
Cc:	Chris Wright <chrisw@...s-sol.org>, linux-kernel@...r.kernel.org,
	Jeff Garzik <jeff@...zik.org>
Subject: Re: [PATCH 49/61] ISDN: fix drivers, by handling errors thrown by ->readstat()

On Wed, Nov 01, 2006 at 08:49:22AM +0100, Willy Tarreau wrote:
> On Tue, Oct 31, 2006 at 09:34:29PM -0800, Chris Wright wrote:
> > -stable review patch.  If anyone has any objections, please let us know.
> > ------------------
> > 
> > From: Jeff Garzik <jeff@...zik.org>
> > 
> > This is a particularly ugly on-failure bug, possibly security, since the
> > lack of error handling here is covering up another class of bug: failure to
> > handle copy_to_user() return values.
> > 
> > The I4L API function ->readstat() returns an integer, and by looking at
> > several existing driver implementations, it is clear that a negative return
> > value was meant to indicate an error.
> > 
> > Given that several drivers already return a negative value indicating an
> > errno-style error, the current code would blindly accept that [negative]
> > value as a valid amount of bytes read.  Obvious damage ensues.
> > 
> > Correcting ->readstat() handling to properly notice errors fixes the
> > existing code to work correctly on error, and enables future patches to
> > more easily indicate errors during operation.
> > 
> > Signed-off-by: Jeff Garzik <jeff@...zik.org>
> > Cc: Karsten Keil <kkeil@...e.de>
> > Cc: <stable@...nel.org>
> > Signed-off-by: Andrew Morton <akpm@...l.org>
> > Signed-off-by: Linus Torvalds <torvalds@...l.org>
> > Signed-off-by: Chris Wright <chrisw@...s-sol.org>
> > ---
> >  drivers/isdn/i4l/isdn_common.c |    9 ++++++---
> >  1 file changed, 6 insertions(+), 3 deletions(-)
> > 
> > --- linux-2.6.18.1.orig/drivers/isdn/i4l/isdn_common.c
> > +++ linux-2.6.18.1/drivers/isdn/i4l/isdn_common.c
> > @@ -1134,9 +1134,12 @@ isdn_read(struct file *file, char __user
> >  		if (dev->drv[drvidx]->interface->readstat) {
> >  			if (count > dev->drv[drvidx]->stavail)
> >  				count = dev->drv[drvidx]->stavail;
> > -			len = dev->drv[drvidx]->interface->
> > -				readstat(buf, count, drvidx,
> > -					 isdn_minor2chan(minor));
> > +			len = dev->drv[drvidx]->interface->readstat(buf, count,
> > +						drvidx, isdn_minor2chan(minor));
> > +			if (len < 0) {
> > +				retval = len;
> > +				goto out;
> > +			}
> >  		} else {
> >  			len = 0;
> >  		}
> 
> Seems appropriate for 2.4 too. Jeff, Karsten, no objection ?
> 

Yes, OK for me.

-- 
Karsten Keil
SuSE Labs
ISDN development
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