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

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Date:   Thu, 10 Aug 2017 13:21:55 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Phil Elwell <phil@...pberrypi.org>
Cc:     Eric Anholt <eric@...olt.net>,
        Stefan Wahren <stefan.wahren@...e.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Aishwarya Pant <aishpant@...il.com>,
        linux-rpi-kernel@...ts.infradead.org, devel@...verdev.osuosl.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] staging: bcm2835-audio: Fix memory corruption

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.

> 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@...pberrypi.org>
> 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().

>  			ret = -EIO;
>  			goto err_free_mem;

This label name is out of date.  There is a later error path where
vc_vchi_audio_init() fails and we leak on that path.  Also why is
vchi_instance a static variable?  Arglebargleblargleblah...

regards,
dan carpenter