[PATCH] ALSA: bebob: potential info leak in hwdep_read()

[Takashi Sakamoto]

Oops, I forgot to add my tag to the former message.

Acked-by: Takashi Sakamoto <o-takashi at sakamocchi.jp>

On Wed, Oct 07, 2020 at 10:04:37PM +0900, Takashi Sakamoto wrote:
> Hi,
> 
> Thanks for the patch.
> 
> On Wed, Oct 07, 2020 at 10:49:28AM +0300, Dan Carpenter wrote:
> > The "count" variable needs to be capped on every path so that we don't
> > copy too much information to the user.
> > 
> > Fixes: 618eabeae711 ("ALSA: bebob: Add hwdep interface")
> > Signed-off-by: Dan Carpenter <dan.carpenter at oracle.com>
> > ---
> >  sound/firewire/bebob/bebob_hwdep.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> > 
> > diff --git a/sound/firewire/bebob/bebob_hwdep.c b/sound/firewire/bebob/bebob_hwdep.c
> > index 45b740f44c45..c362eb38ab90 100644
> > --- a/sound/firewire/bebob/bebob_hwdep.c
> > +++ b/sound/firewire/bebob/bebob_hwdep.c
> > @@ -36,12 +36,11 @@ hwdep_read(struct snd_hwdep *hwdep, char __user *buf,  long count,
> >  	}
> >  
> >  	memset(&event, 0, sizeof(event));
> > +	count = min_t(long, count, sizeof(event.lock_status));
> >  	if (bebob->dev_lock_changed) {
> >  		event.lock_status.type = SNDRV_FIREWIRE_EVENT_LOCK_STATUS;
> >  		event.lock_status.status = (bebob->dev_lock_count > 0);
> >  		bebob->dev_lock_changed = false;
> > -
> > -		count = min_t(long, count, sizeof(event.lock_status));
> >  	}
> >  
> >  	spin_unlock_irq(&bebob->lock);
> > -- 
> > 2.28.0
> 
> Indeed, the bug can leak the contents of kernel memory into user space
> unintentionally for the size indicated by ALSA HwDep application...
> 
> I will check the other drivers in ALSA firewire stack later for safe.
> 
> 
> Thanks
> 
> Takashi Sakamoto