media: gspca/sunplus: fix zero-length control requests

The direction of the pipe argument must match the request-type direction
bit or control requests may fail depending on the host-controller-driver
implementation.

Control transfers without a data stage are treated as OUT requests by
the USB stack and should be using usb_sndctrlpipe(). Failing to do so
will now trigger a warning.

Fix the single zero-length control request which was using the
read-register helper, and update the helper so that zero-length reads
fail with an error message instead.

Fixes: 6a7eba2 ("V4L/DVB (8157): gspca: all subdrivers")
Cc: stable@vger.kernel.org      # 2.6.27
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/media/usb/gspca/sunplus.c

@@ -242,6 +242,10 @@ static void reg_r(struct gspca_dev *gspca_dev,
 		gspca_err(gspca_dev, "reg_r: buffer overflow\n");
 		return;
 	}
+	if (len == 0) {
+		gspca_err(gspca_dev, "reg_r: zero-length read\n");
+		return;
+	}
 	if (gspca_dev->usb_err < 0)
 		return;
 	ret = usb_control_msg(gspca_dev->dev,
@@ -250,7 +254,7 @@ static void reg_r(struct gspca_dev *gspca_dev,
 			USB_DIR_IN | USB_TYPE_VENDOR | USB_RECIP_DEVICE,
 			0,		/* value */
 			index,
-			len ? gspca_dev->usb_buf : NULL, len,
+			gspca_dev->usb_buf, len,
 			500);
 	if (ret < 0) {
 		pr_err("reg_r err %d\n", ret);
@@ -727,7 +731,7 @@ static int sd_start(struct gspca_dev *gspca_dev)
 		case MegaImageVI:
 			reg_w_riv(gspca_dev, 0xf0, 0, 0);
 			spca504B_WaitCmdStatus(gspca_dev);
-			reg_r(gspca_dev, 0xf0, 4, 0);
+			reg_w_riv(gspca_dev, 0xf0, 4, 0);
 			spca504B_WaitCmdStatus(gspca_dev);
 			break;
 		default: