Re: [PATVH] media, dvb, IX2505V: Remember to free allocated memoryin failure path (ix2505v_attach()).

[Jesper Juhl]

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@xxxxxxxxxxxxx>
> > ---
> >  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?


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