[libcamera-devel] [PATCH] v4l2: Accept read-only buffers mappings and require MAP_SHARED

[Nejc Galof]

Hello.
Tomorrow I will test and send you an answer.

Thank you
Nejc Galof

V V pet., 28. jan. 2022 ob 23:00 je oseba Laurent Pinchart <
laurent.pinchart at ideasonboard.com> napisala:

> V4L2 is happy to map buffers read-only for capture devices (but rejects
> write-only mappings). We can support this as the dmabuf mmap()
> implementation supports it. This change fixes usage of the V4L2
> compatibility layer with OpenCV.
>
> While at it, attempt to validate the other flags. videobuf2 requires
> MAP_SHARED and doesn't check other flags, so mimic the same behaviour.
> While unlikly, other flags could get rejected by other kernel layers for
> V4L2 buffers but not for dmabuf. This can be handled later if the need
> arises.
>
> Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> ---
>  src/v4l2/v4l2_camera_proxy.cpp | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
>
> Nejc, could you please test this patch ? It's slightly different than
> the one I've shared on the IRC channel. If you don't mind appearing in
> the git development history, you can reply with
>
> Tested-by: Name <email at address>
>
> and I'll add that (as well as a corresponding Reported-by tag) to the
> commit before pushing it.
>
> diff --git a/src/v4l2/v4l2_camera_proxy.cpp
> b/src/v4l2/v4l2_camera_proxy.cpp
> index f3470a6d312a..ebe7601a4ba6 100644
> --- a/src/v4l2/v4l2_camera_proxy.cpp
> +++ b/src/v4l2/v4l2_camera_proxy.cpp
> @@ -104,8 +104,17 @@ void *V4L2CameraProxy::mmap(V4L2CameraFile *file,
> void *addr, size_t length,
>
>         MutexLocker locker(proxyMutex_);
>
> -       /* \todo Validate prot and flags properly. */
> -       if (prot != (PROT_READ | PROT_WRITE)) {
> +       /*
> +        * Mimic the videobuf2 behaviour, which requires PROT_READ. Reject
> +        * PROT_EXEC as it makes no sense.
> +        */
> +       if (!(prot & PROT_READ) || prot & PROT_EXEC) {
> +               errno = EINVAL;
> +               return MAP_FAILED;
> +       }
> +
> +       /* videobuf2 also requires MAP_SHARED. */
> +       if (!(flags & MAP_SHARED)) {
>                 errno = EINVAL;
>                 return MAP_FAILED;
>         }
>
> base-commit: 7ea52d2b586144fdc033a3ffc1c4a4bbb99b5440
> --
> Regards,
>
> Laurent Pinchart
>
>
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