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

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Date:	Wed, 1 Nov 2006 08:49:22 +0100
From:	Willy Tarreau <w@....eu>
To:	Chris Wright <chrisw@...s-sol.org>
Cc:	linux-kernel@...r.kernel.org, Jeff Garzik <jeff@...zik.org>,
	Karsten Keil <kkeil@...e.de>
Subject: Re: [PATCH 49/61] ISDN: fix drivers, by handling errors thrown by ->readstat()

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 ?

Willy

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