Re: [PATCH] staging: bcm2835-audio: Fix memory corruption

[Dan Carpenter]

On Thu, Aug 10, 2017 at 11:52:42AM +0100, Phil Elwell wrote:
> On 10/08/2017 11:21, Dan Carpenter wrote:
> > The original patch did not go through the normal review process...
> > 
> > On Tue, Aug 08, 2017 at 01:05:02PM +0100, Phil Elwell wrote:
> >> I'm all for fixing memory leaks, but freeing a block while it is still
> >> being used is a recipe for hard-to-debug kernel exceptions.
> >>
> > 
> > This bug completely breaks the driver doesn't it?  It's not very subtle
> > so it should be easy to diagnose with git bisect.
> 
> It's more subtle than that - the failure isn't consistent, sometimes crashing
> and sometimes not depending on how and when memory is reused.
> 
> >> 1) There is already a vchi method for freeing the instance, so use it.
> >> 2) Only call it on error, and then only before initted is false.
> >>
> >> Signed-off-by: Phil Elwell <phil@xxxxxxxxxxxxxxx>
> >> Fixes: 0adbfd4694c2 ("staging: bcm2835-audio: fix memory leak in bcm2835_audio_open_connection()")
> >> ---
> >>  drivers/staging/vc04_services/bcm2835-audio/bcm2835-vchiq.c | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/staging/vc04_services/bcm2835-audio/bcm2835-vchiq.c b/drivers/staging/vc04_services/bcm2835-audio/bcm2835-vchiq.c
> >> index 5f3d8f2..89f96f3 100644
> >> --- a/drivers/staging/vc04_services/bcm2835-audio/bcm2835-vchiq.c
> >> +++ b/drivers/staging/vc04_services/bcm2835-audio/bcm2835-vchiq.c
> >> @@ -409,6 +409,7 @@ static int bcm2835_audio_open_connection(struct bcm2835_alsa_stream *alsa_stream
> >>  			LOG_ERR("%s: failed to connect VCHI instance (ret=%d)\n",
> >>  				__func__, ret);
> >>  
> >> +			vchi_disconnect(vchi_instance);
> > 
> > This is ugly because why are we calling disconnect() if connect() fails?
> > These functions should be symetric so disconnect only disconnects and
> > we call a different function to undo vchi_initialise().
> 
> Agreed - I'm not going to change the API, but I can add a comment.
> 

Nah...  Please don't do that.  Just create a function:

static void vchiq_free(VCHIQ_INSTANCE_T *vchi_instance)
{
	kfree(vchi_instance);
}

Really vchi_initialise() is badly named and it's just a wrapper around
vchiq_initialise().  It should be deleted and vchiq_initialise() should
be renamed to allocate instead of initialize...  But that's for a
separate patch.

And also we should move the kfree() out of disconnect() like I said
and instead call vchiq_free().  But again, that's for a separate patch.

Change the goto to "return -EIO."  Leave the last error path as-is.
Eventually we will want to break this into two functions, one that
allocates the first vchi_instance and one that calls vc_vchi_audio_init().
But again, there are many patches needed to fix this code.

regards,
dan carpenter