linux-kernel - Re: [PATCH 1/2] media: uvcvideo: Avoid invalid memory access

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Date:   Wed, 1 Dec 2021 06:41:29 +0100
From:   Ricardo Ribalda <ribalda@...omium.org>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] media: uvcvideo: Avoid invalid memory access

Hi Laurent

Thanks for the prompt reply :)

On Wed, 1 Dec 2021 at 03:37, Laurent Pinchart
<laurent.pinchart@...asonboard.com> wrote:
>
> Hi Ricardo,
>
> Thank you for the patch.
>
> On Tue, Nov 30, 2021 at 03:50:25PM +0000, Ricardo Ribalda wrote:
> > If mappings points to an invalid memory, we will be invalid accessing
> > it.
> > Solve it by initializing the value of the variable mapping and by
> > changing the order in the conditional statement (to avoid accessing
> > mapping->id if not needed).
> >
> > Fix:
> > kasan: GPF could be caused by NULL-ptr deref or user memory access
> > general protection fault: 0000 [#1] PREEMPT SMP KASAN NOPTI
> >
> > Fixes: 6350d6a4ed487 ("media: uvcvideo: Set error_idx during ctrl_commit errors")
> > Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> > ---
> >  drivers/media/usb/uvc/uvc_ctrl.c | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
> > index 30bfe9069a1fb..f7b7add3cfa59 100644
> > --- a/drivers/media/usb/uvc/uvc_ctrl.c
> > +++ b/drivers/media/usb/uvc/uvc_ctrl.c
> > @@ -852,8 +852,8 @@ static void __uvc_find_control(struct uvc_entity *entity, u32 v4l2_id,
> >                               return;
> >                       }
> >
> > -                     if ((*mapping == NULL || (*mapping)->id > map->id) &&
> > -                         (map->id > v4l2_id) && next) {
> > +                     if (next && (map->id > v4l2_id) &&
> > +                         (*mapping == NULL || (*mapping)->id > map->id)) {
> >                               *control = ctrl;
> >                               *mapping = map;
> >                       }
> > @@ -1638,7 +1638,7 @@ static int uvc_ctrl_find_ctrl_idx(struct uvc_entity *entity,
> >                                 struct v4l2_ext_controls *ctrls,
> >                                 struct uvc_control *uvc_control)
> >  {
> > -     struct uvc_control_mapping *mapping;
> > +     struct uvc_control_mapping *mapping = NULL;
>
> It seems to me that either change will fix the bug, we don't need both,
> is that right ? If so I'd drop the change to __uvc_find_control(), as it
> seems quite fragile to allow mapping to be uninitialized.

Just wanted to be extra paranoid. I have just sent a v2 of the patch.

Thanks!

>
> >       struct uvc_control *ctrl_found;
> >       unsigned int i;
> >
>
> --
> Regards,
>
> Laurent Pinchart



-- 
Ricardo Ribalda