linux-kernel - Re: [PATCH 3/5 v2] drivers/hid/hid-roccat.c: eliminate a null pointer dereference

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Message-ID: <alpine.LNX.2.00.1110291857310.3541@pobox.suse.cz>
Date:	Sat, 29 Oct 2011 19:00:24 +0200 (CEST)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Julia Lawall <julia@...u.dk>
Cc:	David Herrmann <dh.herrmann@...glemail.com>,
	Arend van Spriel <arend@...adcom.com>,
	Dan Carpenter <dan.carpenter@...cle.com>,
	"kernel-janitors@...r.kernel.org" <kernel-janitors@...r.kernel.org>,
	"linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/5 v2] drivers/hid/hid-roccat.c: eliminate a null pointer
 dereference

On Sat, 29 Oct 2011, Julia Lawall wrote:

> From: Julia Lawall <julia@...u.dk>
> 
> It is not possible to take the lock in device if device is NULL.
> The mutex_lock is thus moved after the NULL test, and the relevant part of
> the shared error handling code is moved up.
> 
> The semantic match that finds this problem is as follows:
> (http://coccinelle.lip6.fr/)
> 
> // <smpl>
> @r@
> expression E, E1;
> identifier f;
> statement S1,S2,S3;
> @@
> 
> if (E == NULL)
> {
>   ... when != if (E == NULL || ...) S1 else S2
>       when != E = E1
> *E->f
>   ... when any
>   return ...;
> }
> else S3
> // </smpl>
> 
> Signed-off-by: Julia Lawall <julia@...u.dk>
> 
> ---
> mutex_lock changed to mutex_unlock in error handling code
> 
>  drivers/hid/hid-roccat.c |    9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/hid/hid-roccat.c b/drivers/hid/hid-roccat.c
> index 2596321..36a28b8 100644
> --- a/drivers/hid/hid-roccat.c
> +++ b/drivers/hid/hid-roccat.c
> @@ -163,14 +163,15 @@ static int roccat_open(struct inode *inode, struct file *file)
>  
>  	device = devices[minor];
>  
> -	mutex_lock(&device->readers_lock);
> -
>  	if (!device) {
>  		pr_emerg("roccat device with minor %d doesn't exist\n", minor);
> -		error = -ENODEV;
> -		goto exit_err;
> +		kfree(reader);
> +		mutex_unlock(&devices_lock);
> +		return -ENODEV;
>  	}
>  
> +	mutex_lock(&device->readers_lock);
> +
>  	if (!device->open++) {
>  		/* power on device on adding first reader */
>  		error = hid_hw_power(device->hid, PM_HINT_FULLON);

Julia,

thanks a lot for fixing this.

Could you please redo the patch in a way that it adds second 
'exit_unlock1' label (and renames 'exit_unlock' to 'exit_unlock2') (or 
any appropriate variation of the names) and preserve error path using goto 
instead of mixture of returns and gotos that this patch would introduce?

Thanks,

-- 
Jiri Kosina
SUSE Labs
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