Subject: Re: [PATCH] ibmasm driver: don't use previously freed pointer
From: Max Asbock <masbock@us.ibm.com>
To: Greg KH <greg@kroah.com>
Cc: linux-kernel@vger.kernel.org
In-Reply-To: <20060204060254.GA4454@kroah.com>
References: <1139005598.7521.68.camel@w-amax>
	 <20060204060254.GA4454@kroah.com>
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Date: Tue, 07 Feb 2006 09:29:17 -0800
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On Fri, 2006-02-03 at 22:02, Greg KH wrote:
> On Fri, Feb 03, 2006 at 02:26:38PM -0800, Max Asbock wrote:
> > ibmasm driver:
> > Fix the command_put() function which uses a pointer for a spinlock that
> > can be freed before dereferencing it.
> > 
> > Signed-off-by: Max Asbock masbock@us.ibm.com
> > 
> > ---
> > 
> > diff -burpN linux-2.6.16-rc1/drivers/misc/ibmasm/ibmasm.h linux-2.6.16-rc1.ibmasm/drivers/misc/ibmasm/ibmasm.h
> > --- linux-2.6.16-rc1/drivers/misc/ibmasm/ibmasm.h	2006-02-01 11:50:01.000000000 -0800
> > +++ linux-2.6.16-rc1.ibmasm/drivers/misc/ibmasm/ibmasm.h	2006-02-03 13:57:42.000000000 -0800
> > @@ -101,10 +101,11 @@ struct command {
> >  static inline void command_put(struct command *cmd)
> >  {
> >  	unsigned long flags;
> > +	spinlock_t *lock = cmd->lock;
> >  
> > -	spin_lock_irqsave(cmd->lock, flags);
> > +	spin_lock_irqsave(lock, flags);
> >          kobject_put(&cmd->kobj);
> > -	spin_unlock_irqrestore(cmd->lock, flags);
> > +	spin_unlock_irqrestore(lock, flags);
> >  }
> 
> If this patch is true, doesn't the spinlock the pointer is pointing out
> still get deleted?
> 
> Yes you save a pointer off, but it looks like the problem is still
> present.
> 
> Or am I missing something?
> 

The lock pointer in struct command points to a spinlock outside the
structure that doesn't get deleted.

max

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