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

[Ezequiel Garcia <ezequiel@collabora.com>]

On Fri, 2019-02-15 at 17:05 +0100, Hans Verkuil wrote:
> On 2/15/19 4:52 PM, Ezequiel Garcia wrote:
> > On Thu, 2019-01-10 at 14:43 +0200, 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;
> > >  		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);
> > 
> > I'm under the impression this commit is causing the following v4l2-compliance warning:
> > 
> > TRY_FMT cannot handle an invalid pixelformat.
> > This may or may not be a problem. For more information see:
> > http://www.mail-archive.com/linux-media@vger.kernel.org/msg56550.html
> > 
> > This applies to try_fmt and s_fmt.
> > 
> > After checking the v4l2 spec, it seems we can only error on a bad type field [1]:
> > 
> > "Drivers should not return an error code unless the type field is invalid".
> > 
> > Perhaps we can clamp num_planes to VIDEO_MAX_PLANES, instead of erroring out?
> 
> Yes, that would be the right approach.
> 
> Ezequiel, can you clamp num_planes and test the patch? And post it if it fixes the
> warning?
> 

I can try :-)

> This really should have been caught by testing with e.g. vivid and v4l2-compliance.
> 

We need a CI!

> Regards,
> 
> 	Hans
> 
> > [1] https://www.kernel.org/doc/html/latest/media/uapi/v4l/vidioc-g-fmt.html
> > 
> > Regards,
> > Eze
> >