linux-kernel - Re: [PATCH] drivers/media/video: avoid NULL dereference

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Message-Id: <20100322231441.b7e33bf9.akpm@linux-foundation.org>
Date:	Mon, 22 Mar 2010 23:14:41 -0400
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Julia Lawall <julia@...u.dk>
Cc:	Mark McClelland <mmcclell@...foot.com>,
	Mauro Carvalho Chehab <mchehab@...radead.org>,
	linux-usb@...r.kernel.org, linux-media@...r.kernel.org,
	linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] drivers/media/video: avoid NULL dereference

On Sun, 21 Mar 2010 22:31:06 +0100 (CET) Julia Lawall <julia@...u.dk> wrote:

> From: Julia Lawall <julia@...u.dk>
> 
> If ov is NULL, it will not be possible to take the lock in the first place,
> so move the test up earlier.
> 
> ...
>
> --- a/drivers/media/video/ov511.c
> +++ b/drivers/media/video/ov511.c
> @@ -5913,14 +5913,12 @@ ov51x_disconnect(struct usb_interface *intf)
>  
>  	PDEBUG(3, "");
>  
> +	if (!ov)
> +		return;
> +
>  	mutex_lock(&ov->lock);
>  	usb_set_intfdata (intf, NULL);
>  
> -	if (!ov) {
> -		mutex_unlock(&ov->lock);
> -		return;
> -	}
> -
>  	/* Free device number */
>  	ov511_devused &= ~(1 << ov->nr);

I think we can pretty safely assume that we never get here with ov==NULL.

Oh well, I'll leave the test there for others to ponder.
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