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

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Message-ID: <Pine.LNX.4.64.1110292016290.10808@ask.diku.dk>
Date:	Sat, 29 Oct 2011 20:18:26 +0200 (CEST)
From:	Julia Lawall <julia@...u.dk>
To:	Jiri Kosina <jkosina@...e.cz>
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, Jiri Kosina wrote:

> 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?

OK.  At first I couldn't see how to do this without duplicating the 
unlocks in the success and failure cases, but perhaps there is a solution 
by adding more gotos.  I'll try for that.

julia
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