media: dib0700: fix undefined behavior in tuner shutdown

This fixes a problem where closing the tuner would leave it in a state where it would not tune to any channel when reopened. This problem was discovered as part of https://github.com/hselasky/webcamd/issues/16.

Since adap->id is 0 or 1, this bit-shift overflows, which is undefined behavior. The driver still worked in practice as the overflow would in most environments result in 0, which rendered the line a no-op. When running the driver as part of webcamd however, the overflow could lead to 0xff due to optimizations by the compiler, which would, in the end, improperly shut down the tuner.

The bug is a regression introduced in the commit referenced below. The present patch causes identical behavior to before that commit for adap->id equal to 0 or 1. The driver does not contain support for dib0700 devices with more adapters, assuming such even exist.

Tests have been performed with the Xbox One Digital TV Tuner on amd64. Not all dib0700 devices are expected to be affected by the regression; this code path is only taken by those with incorrect endpoint numbers.

---
 drivers/media/usb/dvb-usb/dib0700_core.c | 2 --
 1 file changed, 2 deletions(-)

index 70219b3e8566..7ea8f68b0f45 100644
@@ -618,8 +618,6 @@ int dib0700_streaming_ctrl(struct dvb_usb_adapter *adap, int onoff)
 		deb_info("the endpoint number (%i) is not correct, use the adapter id instead", adap->fe_adap[0].stream.props.endpoint);
 		if (onoff)
 			st->channel_state |=	1 << (adap->id);
-		else
-			st->channel_state |=	1 << ~(adap->id);
 	} else {
 		if (onoff)
 			st->channel_state |=	1 << (adap->fe_adap[0].stream.props.endpoint-2);

2.30.1 (Apple Git-130)