[PATCH] media: v4l2-ioctl: prevent underflow in v4l_enumoutput()

[Dan Carpenter <dan.carpenter@xxxxxxxxxx>]

My Smatch allmodconfig build only detects one function implementing
vpbe_device_ops->enum_outputs and that's vpbe_enum_outputs().  The
problem really happens in that function when we do:

	int temp_index = output->index;

	if (temp_index >= cfg->num_outputs)
		return -EINVAL;

Unfortunately, both temp_index and cfg->num_outputs are type int so we
have a potential read before the start of the array if "temp_index" is
negative.

I could have fixed the bug in that function but it's more secure and
future proof to block that bug earlier in a central place.  There is no
one who need p->index to be more than INT_MAX.

Fixes: 66715cdc3224 ("[media] davinci vpbe: VPBE display driver")
Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>

diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
index a40dbec271f1..115757ab8bc0 100644
--- a/drivers/media/v4l2-core/v4l2-ioctl.c
+++ b/drivers/media/v4l2-core/v4l2-ioctl.c
@@ -1099,6 +1099,9 @@ static int v4l_enumoutput(const struct v4l2_ioctl_ops *ops,
 	if (is_valid_ioctl(vfd, VIDIOC_S_STD))
 		p->capabilities |= V4L2_OUT_CAP_STD;
 
+	if (p->index > INT_MAX)
+		return -EINVAL;
+
 	return ops->vidioc_enum_output(file, fh, p);
 }