linux-kernel - Re: [PATVH] media, dvb, IX2505V: Remember to free allocated memory in failure path (ix2505v

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Date:	Fri, 31 Dec 2010 18:33:55 +0000
From:	Malcolm Priestley <tvboxspy@...il.com>
To:	Jesper Juhl <jj@...osbits.net>
Cc:	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
	Mauro Carvalho Chehab <mchehab@...radead.org>
Subject: Re: [PATVH] media, dvb, IX2505V: Remember to free allocated memory
 in failure path (ix2505v_attach()).

On Fri, 2010-12-31 at 15:51 +0100, Jesper Juhl wrote:
> On Fri, 31 Dec 2010, Malcolm Priestley wrote:
> 
> > On Fri, 2010-12-31 at 00:11 +0100, Jesper Juhl wrote:
> > > Hi,
> > > 
> > > We may leak the storage allocated to 'state' in 
> > > drivers/media/dvb/frontends/ix2505v.c::ix2505v_attach() on error.
> > > This patch makes sure we free the allocated memory in the failure case.
> > > 
> > > 
> > > Signed-off-by: Jesper Juhl <jj@...osbits.net>
> > > ---
> > >  ix2505v.c |    1 +
> > >  1 file changed, 1 insertion(+)
> > > 
> > >   Compile tested only.
> > > 
> > > diff --git a/drivers/media/dvb/frontends/ix2505v.c b/drivers/media/dvb/frontends/ix2505v.c
> > > index 55f2eba..fcb173d 100644
> > > --- a/drivers/media/dvb/frontends/ix2505v.c
> > > +++ b/drivers/media/dvb/frontends/ix2505v.c
> > > @@ -293,6 +293,7 @@ struct dvb_frontend *ix2505v_attach(struct dvb_frontend *fe,
> > >  		ret = ix2505v_read_status_reg(state);
> > >  
> > >  		if (ret & 0x80) {
> > > +			kfree(state);
> > >  			deb_i2c("%s: No IX2505V found\n", __func__);
> > >  			goto error;
> > >  		}
> > > 
> > Memory is freed in... 
> > 
> > error:
> > 	ix2505v_release(fe);
> > 	return NULL;
> > 
> > via...
> > 
> > static int ix2505v_release(struct dvb_frontend *fe)
> > {
> > 	struct ix2505v_state *state = fe->tuner_priv;
> > 
> > 	fe->tuner_priv = NULL;
> > 	kfree(state);
> > 
> > 	return 0;
> > }
> > 
> 
> Except that 'state' has not been assigned to fe->tuner_priv at this 
> point, so ix2505v_release() cannot free the memory that was just 
> allocated with kzalloc().
> 
> 
>   state is a local variable:
>   		struct ix2505v_state *state = NULL;
> 		...
> 
>   we allocate memory and assign it to 'state' here:
>   		state = kzalloc(sizeof(struct ix2505v_state), GFP_KERNEL);
>   		if (NULL == state)
>   			return NULL;
>   	
>   		state->config = config;
>   		state->i2c = i2c;
>   	
>   here 'state' is used, but not in a way that saves it anywhere:
>   		if (state->config->tuner_write_only) {
>   			if (fe->ops.i2c_gate_ctrl)
>   				fe->ops.i2c_gate_ctrl(fe, 1);
>   	
>   this function call involves 'state' but it does not save it anywhere
>   either:
>   			ret = ix2505v_read_status_reg(state);
>   	
>   			if (ret & 0x80) {
>   				deb_i2c("%s: No IX2505V found\n", __func__);
>   so when we jump to error here 'state' still exists only as the local
>   variable, it has not been assigned to anything else.
>   				goto error;
>   			}
>   		...
>   	error:
>   there is no way this function call can free 'state' on this path since
>   it has not been assigned to fe->tuner_priv. 
>   		ix2505v_release(fe);
>   The local variable state goes out of scope here and leaks the memory it
>   points to:
>   		return NULL;
>   	}
> 
> Am I missing something?

Oh, Sorry, I see it now.

Now there is two options.

Either;

1) Move fe->tuner_priv = state to below line 287, so it can be released
by ix2505v_release and fe->tuner_priv returned to NULL;

2) or not calling ix2505v_release changing line 314 to kfree(state).
fe->tuner_priv will remain NULL through out.

Currently, tuner_write_only is not implemented in the dvb-usb-lmedm04
driver, as sometimes it returned unpredictable results, and wrongly
failed to attach the tuner. Although, I will test it again.

Regards


Malcolm

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