Re: [PATCH] uvcvideo: uvc_ctrl_is_accessible: check for INACTIVE

[Ricardo Ribalda <ribalda@chromium.org>]

Hi Hans

On Thu, Mar 25, 2021 at 1:27 PM Hans Verkuil <hverkuil@xs4all.nl> wrote:
>
> On 23/03/2021 16:29, Ricardo Ribalda Delgado wrote:
> > Hi Hans
> >
> > On Mon, Mar 22, 2021 at 1:06 PM Hans Verkuil <hverkuil@xs4all.nl> wrote:
> >>
> >> Check for inactive controls in uvc_ctrl_is_accessible().
> >> Use the new value for the master_id controls if present,
> >> otherwise use the existing value to determine if it is OK
> >> to set the control. Doing this here avoids attempting to
> >> set an inactive control, which will return an error from the
> >> USB device.
> >
> > Dont you think that this patch is not needed if this is used:
> > https://patchwork.linuxtv.org/project/linux-media/patch/20210319170906.278238-17-ribalda@chromium.org/
> > ?
>
> That might well be the case :-)
>
> I haven't really looked at that.

They overlap a bit. Not sure if we can remove one of them. Lets see
what Laurent thinks.

Thanks!

>
> >
> >
> > Also Maybe it is wrong. (Maybe it is the keyword here ;).
> > I think the initial assumption was that uvc_ctrl_is_accessible shall
> > not access the hardware, but with this patch it is accessing it.
>
> It's only accessing it if master_ctrl->loaded is 0 (see __uvc_ctrl_get()).
> If loaded is 0, and __uvc_ctrl_get() returns an error, then that error is
> ignored and the code will assume that the control is accessible.
>
> Note that what we try to avoid is *setting* an inactive control. In this
> case we're reading the master control, which should be safe except for
> USB hardware problems that can return an error.
>
> Regards,
>
>         Hans
>
> >>
> >> Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
> >> ---
> >> Ricardo: this can be added to your uvc series. It avoids attempts to set
> >> inactive controls.
> >> ---
> >>  drivers/media/usb/uvc/uvc_ctrl.c | 28 +++++++++++++++++++++++++++-
> >>  drivers/media/usb/uvc/uvc_v4l2.c |  4 ++--
> >>  drivers/media/usb/uvc/uvcvideo.h |  3 ++-
> >>  3 files changed, 31 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
> >> index d9d4add1e813..6e7b904bc33d 100644
> >> --- a/drivers/media/usb/uvc/uvc_ctrl.c
> >> +++ b/drivers/media/usb/uvc/uvc_ctrl.c
> >> @@ -1047,10 +1047,18 @@ static int uvc_query_v4l2_class(struct uvc_video_chain *chain, u32 req_id,
> >>  }
> >>
> >>  int uvc_ctrl_is_accessible(struct uvc_video_chain *chain, u32 v4l2_id,
> >> -                          bool read)
> >> +                          const struct v4l2_ext_controls *ctrls,
> >> +                          unsigned long ioctl)
> >>  {
> >> +       struct uvc_control_mapping *master_map = NULL;
> >> +       struct uvc_control *master_ctrl = NULL;
> >>         struct uvc_control_mapping *mapping;
> >>         struct uvc_control *ctrl;
> >> +       bool read = ioctl == VIDIOC_G_EXT_CTRLS;
> >> +       bool try = ioctl == VIDIOC_TRY_EXT_CTRLS;
> >> +       s32 val;
> >> +       int ret;
> >> +       int i;
> >>
> >>         if (__uvc_query_v4l2_class(chain, v4l2_id, 0) >= 0)
> >>                 return -EACCES;
> >> @@ -1065,6 +1073,24 @@ int uvc_ctrl_is_accessible(struct uvc_video_chain *chain, u32 v4l2_id,
> >>         if (!(ctrl->info.flags & UVC_CTRL_FLAG_SET_CUR) && !read)
> >>                 return -EACCES;
> >>
> >> +       if (read || try || !mapping->master_id)
> >> +               return 0;
> >> +
> >> +       for (i = ctrls->count - 1; i >= 0; i--)
> >> +               if (ctrls->controls[i].id == mapping->master_id)
> >> +                       return ctrls->controls[i].value ==
> >> +                                       mapping->master_manual ? 0 : -EACCES;
> >> +
> >> +       __uvc_find_control(ctrl->entity, mapping->master_id, &master_map,
> >> +                          &master_ctrl, 0);
> >> +
> >> +       if (!master_ctrl || !(master_ctrl->info.flags & UVC_CTRL_FLAG_GET_CUR))
> >> +               return 0;
> >> +
> >> +       ret = __uvc_ctrl_get(chain, master_ctrl, master_map, &val);
> >> +       if (ret >= 0 && val != mapping->master_manual)
> >> +               return -EACCES;
> >> +
> >>         return 0;
> >>  }
> >>
> >> diff --git a/drivers/media/usb/uvc/uvc_v4l2.c b/drivers/media/usb/uvc/uvc_v4l2.c
> >> index 12362e0f9870..e40db7ae18b1 100644
> >> --- a/drivers/media/usb/uvc/uvc_v4l2.c
> >> +++ b/drivers/media/usb/uvc/uvc_v4l2.c
> >> @@ -803,8 +803,8 @@ static int uvc_ctrl_check_access(struct uvc_video_chain *chain,
> >>         int ret = 0;
> >>
> >>         for (i = 0; i < ctrls->count; ++ctrl, ++i) {
> >> -               ret = uvc_ctrl_is_accessible(chain, ctrl->id,
> >> -                                           ioctl == VIDIOC_G_EXT_CTRLS);
> >> +               ret = uvc_ctrl_is_accessible(chain, ctrl->id, ctrls,
> >> +                                           ioctl);
> >>                 if (ret)
> >>                         break;
> >>         }
> >> diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
> >> index aedb4d3d4db9..8849d7953767 100644
> >> --- a/drivers/media/usb/uvc/uvcvideo.h
> >> +++ b/drivers/media/usb/uvc/uvcvideo.h
> >> @@ -869,7 +869,8 @@ static inline int uvc_ctrl_rollback(struct uvc_fh *handle)
> >>  int uvc_ctrl_get(struct uvc_video_chain *chain, struct v4l2_ext_control *xctrl);
> >>  int uvc_ctrl_set(struct uvc_fh *handle, struct v4l2_ext_control *xctrl);
> >>  int uvc_ctrl_is_accessible(struct uvc_video_chain *chain, u32 v4l2_id,
> >> -                          bool read);
> >> +                          const struct v4l2_ext_controls *ctrls,
> >> +                          unsigned long ioctl);
> >>
> >>  int uvc_xu_ctrl_query(struct uvc_video_chain *chain,
> >>                       struct uvc_xu_control_query *xqry);
> >> --
> >> 2.30.0
> >>
> >>
> >
> >
>


--
Ricardo Ribalda