linux-kernel - Re: [PATCH] tm6000: Don't use pointer after freeing it in tm6000_ir

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Date:	Fri, 10 Feb 2012 00:55:07 +0100 (CET)
From:	Jesper Juhl <jj@...osbits.net>
To:	Thierry Reding <thierry.reding@...onic-design.de>
cc:	Mauro Carvalho Chehab <mchehab@...radead.org>,
	Dan Carpenter <dan.carpenter@...cle.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Curtis McEnroe <programble@...il.com>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tm6000: Don't use pointer after freeing it in
 tm6000_ir_fini()

On Mon, 6 Feb 2012, Thierry Reding wrote:

> * Jesper Juhl wrote:
> > In tm6000_ir_fini() there seems to be a problem. 
> > rc_unregister_device(ir->rc); calls rc_free_device() on the pointer it is 
> > given, which frees it.
> > 
> > Subsequently the function does:
> > 
> >   if (!ir->polling)
> >     __tm6000_ir_int_stop(ir->rc);
> > 
> > and __tm6000_ir_int_stop() dereferences the pointer it is given, which
> > has already been freed.
> > 
> > and it also does:
> > 
> >   tm6000_ir_stop(ir->rc);
> > 
> > which also dereferences the (already freed) pointer.
> > 
> > So, it seems that the call to rc_unregister_device() should be move
> > below the calls to __tm6000_ir_int_stop() and tm6000_ir_stop(), so
> > those don't operate on a already freed pointer.
> > 
> > But, I must admit that I don't know this code *at all*, so someone who
> > knows the code should take a careful look before applying this
> > patch. It is based purely on inspection of facts of what is beeing
> > freed where and not at all on understanding what the code does or why.
> > I don't even have a means to test it, so beyond testing that the
> > change compiles it has seen no testing what-so-ever.
> > 
> > Anyway, here's a proposed patch.
> > 
> > Signed-off-by: Jesper Juhl <jj@...osbits.net>
> > ---
> >  drivers/media/video/tm6000/tm6000-input.c |    3 +--
> >  1 files changed, 1 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/media/video/tm6000/tm6000-input.c b/drivers/media/video/tm6000/tm6000-input.c
> > index 7844607..859eb90 100644
> > --- a/drivers/media/video/tm6000/tm6000-input.c
> > +++ b/drivers/media/video/tm6000/tm6000-input.c
> > @@ -481,8 +481,6 @@ int tm6000_ir_fini(struct tm6000_core *dev)
> >  
> >  	dprintk(2, "%s\n",__func__);
> >  
> > -	rc_unregister_device(ir->rc);
> > -
> >  	if (!ir->polling)
> >  		__tm6000_ir_int_stop(ir->rc);
> >  
> > @@ -492,6 +490,7 @@ int tm6000_ir_fini(struct tm6000_core *dev)
> >  	tm6000_flash_led(dev, 0);
> >  	ir->pwled = 0;
> >  
> > +	rc_unregister_device(ir->rc);
> >  
> >  	kfree(ir);
> >  	dev->ir = NULL;
> > -- 
> > 1.7.8.4
> 
> Reviewed-by: Thierry Reding <thierry.reding@...onic-design.de>
> 
Thanks :-)

-- 
Jesper Juhl <jj@...osbits.net>       http://www.chaosbits.net/
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