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

Dan Carpenter
2018-05-17T09:05:51Z

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@oracle.com>

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);
}