Re: [PATCH 1/1] v4l: ioctl: Validate num_planes before using it

[Hans Verkuil <hverkuil@xs4all.nl>]

On 01/10/19 14:41, Sakari Ailus wrote:
> On Thu, Jan 10, 2019 at 02:02:14PM +0100, Hans Verkuil wrote:
>> On 01/10/19 13:43, Sakari Ailus wrote:
>>> The for loop to reset the memory of the plane reserved fields runs over
>>> num_planes provided by the user without validating it. Ensure num_planes
>>> is no more than VIDEO_MAX_PLANES before the loop.
>>>
>>> Fixes: 4e1e0eb0e074 ("media: v4l2-ioctl: Zero v4l2_plane_pix_format reserved fields")
>>> Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
>>> ---
>>> Hi folks,
>>>
>>> This patch goes on top of Thierry's patch "media: v4l2-ioctl: Clear only
>>> per-plane reserved fields".
>>>
>>>  drivers/media/v4l2-core/v4l2-ioctl.c | 8 ++++++++
>>>  1 file changed, 8 insertions(+)
>>>
>>> diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
>>> index 392f1228af7b5..9e68a608ac6d3 100644
>>> --- a/drivers/media/v4l2-core/v4l2-ioctl.c
>>> +++ b/drivers/media/v4l2-core/v4l2-ioctl.c
>>> @@ -1551,6 +1551,8 @@ static int v4l_s_fmt(const struct v4l2_ioctl_ops *ops,
>>>  		if (unlikely(!ops->vidioc_s_fmt_vid_cap_mplane))
>>>  			break;
>>>  		CLEAR_AFTER_FIELD(p, fmt.pix_mp.xfer_func);
>>> +		if (p->fmt.pix_mp.num_planes > VIDEO_MAX_PLANES)
>>> +			break;
>>
>> I would check this not here but in check_fmt: all *_FMT ioctls call that function
>> first, so it makes sense to do the check there.
> 
> Even G_FMT? I'm not saying no though. There's just a slight chance of
> breaking something as it hasn't been a problem to call G_FMT with incorrect
> number of planes in the mplane format; the number would be overwritten
> anyway.

Not G_FMT since everything after the type field is zeroed.

> Apart from that, this leaves just the four locations --- putting this to a
> separate function will reduce the calls to that function to just two.

I was a bit too quick with my comment about check_fmt. Your original patch
is fine.

I'll Ack your patch.

Regards,

	Hans

> 
>>
>> v4l_print_format should also be adjusted (take the minimum of num_planes and
>> VIDEO_MAX_PLANES), since it can still be called even if check_fmt returns an
>> error if num_planes is too large.
>>
>> In fact, the change to v4l_print_format should be a separate patch since that
>> should be backported. It can leak memory in the kernel log if num_planes is
>> too large.
>>
>> Regards,
>>
>> 	Hans
>>
>>>  		for (i = 0; i < p->fmt.pix_mp.num_planes; i++)
>>>  			CLEAR_AFTER_FIELD(&p->fmt.pix_mp.plane_fmt[i], bytesperline);
>>>  		return ops->vidioc_s_fmt_vid_cap_mplane(file, fh, arg);
>>> @@ -1581,6 +1583,8 @@ static int v4l_s_fmt(const struct v4l2_ioctl_ops *ops,
>>>  		if (unlikely(!ops->vidioc_s_fmt_vid_out_mplane))
>>>  			break;
>>>  		CLEAR_AFTER_FIELD(p, fmt.pix_mp.xfer_func);
>>> +		if (p->fmt.pix_mp.num_planes > VIDEO_MAX_PLANES)
>>> +			break;
>>>  		for (i = 0; i < p->fmt.pix_mp.num_planes; i++)
>>>  			CLEAR_AFTER_FIELD(&p->fmt.pix_mp.plane_fmt[i], bytesperline);
>>>  		return ops->vidioc_s_fmt_vid_out_mplane(file, fh, arg);
>>> @@ -1648,6 +1652,8 @@ static int v4l_try_fmt(const struct v4l2_ioctl_ops *ops,
>>>  		if (unlikely(!ops->vidioc_try_fmt_vid_cap_mplane))
>>>  			break;
>>>  		CLEAR_AFTER_FIELD(p, fmt.pix_mp.xfer_func);
>>> +		if (p->fmt.pix_mp.num_planes > VIDEO_MAX_PLANES)
>>> +			break;
>>>  		for (i = 0; i < p->fmt.pix_mp.num_planes; i++)
>>>  			CLEAR_AFTER_FIELD(&p->fmt.pix_mp.plane_fmt[i], bytesperline);
>>>  		return ops->vidioc_try_fmt_vid_cap_mplane(file, fh, arg);
>>> @@ -1678,6 +1684,8 @@ static int v4l_try_fmt(const struct v4l2_ioctl_ops *ops,
>>>  		if (unlikely(!ops->vidioc_try_fmt_vid_out_mplane))
>>>  			break;
>>>  		CLEAR_AFTER_FIELD(p, fmt.pix_mp.xfer_func);
>>> +		if (p->fmt.pix_mp.num_planes > VIDEO_MAX_PLANES)
>>> +			break;
>>>  		for (i = 0; i < p->fmt.pix_mp.num_planes; i++)
>>>  			CLEAR_AFTER_FIELD(&p->fmt.pix_mp.plane_fmt[i], bytesperline);
>>>  		return ops->vidioc_try_fmt_vid_out_mplane(file, fh, arg);
>>>
>>
>