linux-kernel - Re: [PATCH] media: dvb-usb: Fix unexpected infinite loop in dvb_usb_read_remote

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Date: Tue, 30 Apr 2024 09:04:07 +0100
From: Sean Young <sean@...s.org>
To: Zheng Yejian <zhengyejian1@...wei.com>
Cc: mchehab@...nel.org, linux-media@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: dvb-usb: Fix unexpected infinite loop in
 dvb_usb_read_remote_control()

On Mon, Apr 29, 2024 at 07:24:21PM +0800, Zheng Yejian wrote:
> On 2024/4/12 21:52, Zheng Yejian wrote:
> > Infinite log printing occurs during fuzz test:
> > 
> >    rc rc1: DViCO FusionHDTV DVB-T USB (LGZ201) as ...
> >    ...
> >    dvb-usb: schedule remote query interval to 100 msecs.
> >    dvb-usb: DViCO FusionHDTV DVB-T USB (LGZ201) successfully initialized ...
> >    dvb-usb: bulk message failed: -22 (1/0)
> >    dvb-usb: bulk message failed: -22 (1/0)
> >    dvb-usb: bulk message failed: -22 (1/0)
> >    ...
> >    dvb-usb: bulk message failed: -22 (1/0)
> > 
> > Looking into the codes, there is a loop in dvb_usb_read_remote_control(),
> > that is in rc_core_dvb_usb_remote_init() create a work that will call
> > dvb_usb_read_remote_control(), and this work will reschedule itself at
> > 'rc_interval' intervals to recursively call dvb_usb_read_remote_control(),
> > see following code snippet:
> > 
> >    rc_core_dvb_usb_remote_init() {
> >      ...
> >      INIT_DELAYED_WORK(&d->rc_query_work, dvb_usb_read_remote_control);
> >      schedule_delayed_work(&d->rc_query_work,
> >                            msecs_to_jiffies(rc_interval));
> >      ...
> >    }
> > 
> >    dvb_usb_read_remote_control() {
> >      ...
> >      err = d->props.rc.core.rc_query(d);
> >      if (err)
> >        err(...)  // Did not return even if query failed
> >      schedule_delayed_work(&d->rc_query_work,
> >                            msecs_to_jiffies(rc_interval));
> >    }
> > 
> > When the infinite log printing occurs, the query callback
> > 'd->props.rc.core.rc_query' is cxusb_rc_query(). And the log is due to
> > the failure of finding a valid 'generic_bulk_ctrl_endpoint'
> > in usb_bulk_msg(), see following code snippet:
> > 
> >    cxusb_rc_query() {
> >      cxusb_ctrl_msg() {
> >        dvb_usb_generic_rw() {
> >          ret = usb_bulk_msg(d->udev, usb_sndbulkpipe(d->udev,
> >                             d->props.generic_bulk_ctrl_endpoint),...);
> >          if (ret)
> >            err("bulk message failed: %d (%d/%d)",ret,wlen,actlen);
> >            ...
> >        }
> >    ...
> >    }
> > 
> > By analyzing the corresponding USB descriptor, it shows that the
> > bNumEndpoints is 0 in its interface descriptor, but
> > the 'generic_bulk_ctrl_endpoint' is 1, that means user don't configure
> > a valid endpoint for 'generic_bulk_ctrl_endpoint', therefore this
> > 'invalid' USB device should be rejected before it calls into
> > dvb_usb_read_remote_control().
> > 
> > To fix it, iiuc, we can add endpoint check in dvb_usb_adapter_init().
> > 
> > Signed-off-by: Zheng Yejian <zhengyejian1@...wei.com>
> > ---
> >   drivers/media/usb/dvb-usb/dvb-usb-init.c | 8 ++++++++
> >   1 file changed, 8 insertions(+)
> > 
> > Hi, I'm not very familiar with USB driver, and I'm not sure the
> > type check is appropriate or not here. Would be any device properties
> > that allow 'generic_bulk_ctrl_endpoint' not being configured, or would
> > it be configured late after init ? :)
> > 
> 
> Kindly ping :)
> Hi, Mauro, would you mind taking a look at this code ?
> 
> --
> Thanks,
> Zheng Yejian
> 
> > diff --git a/drivers/media/usb/dvb-usb/dvb-usb-init.c b/drivers/media/usb/dvb-usb/dvb-usb-init.c
> > index fbf58012becd..48e7b9fb93dd 100644
> > --- a/drivers/media/usb/dvb-usb/dvb-usb-init.c
> > +++ b/drivers/media/usb/dvb-usb/dvb-usb-init.c
> > @@ -104,6 +104,14 @@ static int dvb_usb_adapter_init(struct dvb_usb_device *d, short *adapter_nrs)
> >   	 * sometimes a timeout occurs, this helps
> >   	 */
> >   	if (d->props.generic_bulk_ctrl_endpoint != 0) {
> > +		ret = usb_pipe_type_check(d->udev, usb_sndbulkpipe(d->udev,
> > +					  d->props.generic_bulk_ctrl_endpoint));
> > +		if (ret)
> > +			goto frontend_init_err;
> > +		ret = usb_pipe_type_check(d->udev, usb_rcvbulkpipe(d->udev,
> > +					  d->props.generic_bulk_ctrl_endpoint));
> > +		if (ret)
> > +			goto frontend_init_err;
> >   		usb_clear_halt(d->udev, usb_sndbulkpipe(d->udev, d->props.generic_bulk_ctrl_endpoint));
> >   		usb_clear_halt(d->udev, usb_rcvbulkpipe(d->udev, d->props.generic_bulk_ctrl_endpoint));
> >   	}
> 

Thank you for your patch.

I think your change looks good. The only comment I have is that the same
check should be done for generic_bulk_ctrl_endpoint_response as well; the
usb_clear_halt() should be done as well, I think.

Thanks

Sean