[media] VIDIOC_ENUM_FREQ_BANDS fix

When VIDIOC_ENUM_FREQ_BANDS is called for a driver that doesn't supply an
enum_freq_bands op, then it will fall back to reporting a single freq band
based on information from g_tuner or g_modulator.

Due to a bug this is an infinite list since the index field wasn't tested.

This patch fixes this and returns -EINVAL if index != 0.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/v4l2-ioctl.c

@@ -1853,6 +1853,8 @@ static int v4l_enum_freq_bands(const struct v4l2_ioctl_ops *ops,
 			.type = type,
 		};
 
+		if (p->index)
+			return -EINVAL;
 		err = ops->vidioc_g_tuner(file, fh, &t);
 		if (err)
 			return err;
@@ -1870,6 +1872,8 @@ static int v4l_enum_freq_bands(const struct v4l2_ioctl_ops *ops,
 
 		if (type != V4L2_TUNER_RADIO)
 			return -EINVAL;
+		if (p->index)
+			return -EINVAL;
 		err = ops->vidioc_g_modulator(file, fh, &m);
 		if (err)
 			return err;