Re: [PATCH v2] media: dvb-usb: Fix unexpected infinite loop in dvb_usb_read_remote_control()

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On 2024/5/3 19:51, Sean Young wrote:
On Tue, Apr 30, 2024 at 06:41:37PM +0800, 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);

   dvb_usb_read_remote_control() {
     err = d->props.rc.core.rc_query(d);
     if (err)
       err(...)  // Did not return even if query failed

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,
         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

To fix it, we need to add endpoint check for 'generic_bulk_ctrl_endpoint'.
And as Sean suggested, the same check and clear halts should be done for
'generic_bulk_ctrl_endpoint_response'. So introduce
dvb_usb_check_bulk_endpoint() to do it for both of them.

Fixes: 4d43e13f723e ("V4L/DVB (4643): Multi-input patch for DVB-USB device")
Signed-off-by: Zheng Yejian <zhengyejian1@xxxxxxxxxx>
  drivers/media/usb/dvb-usb/dvb-usb-init.c | 27 ++++++++++++++++++++----
  1 file changed, 23 insertions(+), 4 deletions(-)

  - As Sean suggested, check endpoint and clear halt for both
    'generic_bulk_ctrl_endpoint' and 'generic_bulk_ctrl_endpoint_response'
    with the new introduced dvb_usb_check_bulk_endpoint();

  - Add Fixes tag.

  - Link:

diff --git a/drivers/media/usb/dvb-usb/dvb-usb-init.c b/drivers/media/usb/dvb-usb/dvb-usb-init.c
index fbf58012becd..7eb321bab84f 100644
--- a/drivers/media/usb/dvb-usb/dvb-usb-init.c
+++ b/drivers/media/usb/dvb-usb/dvb-usb-init.c
@@ -23,6 +23,23 @@ static int dvb_usb_force_pid_filter_usage;
  module_param_named(force_pid_filter_usage, dvb_usb_force_pid_filter_usage, int, 0444);
  MODULE_PARM_DESC(force_pid_filter_usage, "force all dvb-usb-devices to use a PID filter, if any (default: 0).");
+static int dvb_usb_check_bulk_endpoint(struct dvb_usb_device *d, u8 endpoint)
+	if (endpoint) {
+		int ret;
+		ret = usb_pipe_type_check(d->udev, usb_sndbulkpipe(d->udev, endpoint));
+		if (ret)
+			return ret;
+		ret = usb_pipe_type_check(d->udev, usb_rcvbulkpipe(d->udev, endpoint));
+		if (ret)
+			return ret;
+		usb_clear_halt(d->udev, usb_sndbulkpipe(d->udev, endpoint));
+		usb_clear_halt(d->udev, usb_rcvbulkpipe(d->udev, endpoint));
+	}
+	return 0;
  static int dvb_usb_adapter_init(struct dvb_usb_device *d, short *adapter_nrs)
  	struct dvb_usb_adapter *adap;
@@ -103,10 +120,12 @@ static int dvb_usb_adapter_init(struct dvb_usb_device *d, short *adapter_nrs)
  	 * when reloading the driver w/o replugging the device
  	 * sometimes a timeout occurs, this helps
-	if (d->props.generic_bulk_ctrl_endpoint != 0) {
-		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));
-	}
+	ret = dvb_usb_check_bulk_endpoint(d, d->props.generic_bulk_ctrl_endpoint);
+	if (ret)
+		goto frontend_init_err;
+	ret = dvb_usb_check_bulk_endpoint(d, d->props.generic_bulk_ctrl_endpoint_response);
+	if (ret)
+		goto frontend_init_err;
return 0;

This results in the following warning:

drivers/media/usb/dvb-usb/dvb-usb-init.c:133:9: warning: 'adap' may be used uninitialized [-Wmaybe-uninitialized]

I think these tests should be moved to the top of the function, so no cleanup
is required.

Hi, Sean,

I have fixed the warning in v3:,
would you mind taking a look at it ?
I introduce a new funciton dvb_usb_clear_halt() to clear sndbulkpipe and rcvbulkpipe,
dvb_usb_check_bulk_endpoint() only do pipe type check and is moved to the top of
the function.

Zheng Yejian


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