[libcamera-devel] [PATCH] v4l2: v4l2_camera_proxy: Detect ioctl sign-extensions
Paul Elder
paul.elder at ideasonboard.com
Tue Feb 28 07:46:03 CET 2023
On Mon, Feb 27, 2023 at 08:39:47PM +0000, Kieran Bingham via libcamera-devel wrote:
> Handling ioctl's within applications is often wrapped with a helper such
> as xioctl. Unfortunately, there are many instances of xioctl which
> incorrectly handle the correct size of the ioctl request.
>
> This leads to incorrect sign-extension of ioctl's which have bit-31 set,
> and can cause values to be passed into the libcamera's v4l2 adaptation
> layer which no longer represent the true IOCTL code.
>
> We can easily identify if an application has mistakenly sign-extended an
> ioctl command request and mask out those bits.
>
> Do so and report the error loudly, but only once that the application
> should be fixed.
>
> Signed-off-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
> ---
>
> This is a pain. It's not 'libcamera's' fault. But we can do something
> about it.
Welp :/
Yeah we can do something about it. I see a future where the error gets
ignored because it "still works" though.
Reviewed-by: Paul Elder <paul.elder at ideasonboard.com>
>
> See
> - https://github.com/kbingham/libcamera/issues/69
> and
> - https://github.com/Motion-Project/motion/discussions/1636
>
>
>
> src/v4l2/v4l2_camera_proxy.cpp | 18 ++++++++++++++++++
> 1 file changed, 18 insertions(+)
>
> diff --git a/src/v4l2/v4l2_camera_proxy.cpp b/src/v4l2/v4l2_camera_proxy.cpp
> index 55ff62cdb430..75c53aedf2fa 100644
> --- a/src/v4l2/v4l2_camera_proxy.cpp
> +++ b/src/v4l2/v4l2_camera_proxy.cpp
> @@ -782,6 +782,24 @@ int V4L2CameraProxy::ioctl(V4L2CameraFile *file, unsigned long request, void *ar
> {
> MutexLocker locker(proxyMutex_);
>
> + /*
> + * Applications may easily find themselves incorrectly sign-extending
> + * ioctls on 64-bit systems which can cause hard to diagnose failures
> + * with the v4l2-adatation layer. Identify this failure, and work
> + * around it - but report the issue as it should be fixed in the
> + * application.
> + */
> + if (request & 0xffffffff00000000) {
> + static bool warnOnce = true;
> +
> + if (warnOnce) {
> + LOG(V4L2Compat, Error) << "ioctl sign extension detected.";
> + LOG(V4L2Compat, Error) << "Please fix your application.";
> + warnOnce = false;
> + }
> + request &= 0xffffffff;
> + }
> +
> if (!arg && (_IOC_DIR(request) & _IOC_WRITE)) {
> errno = EFAULT;
> return -1;
> --
> 2.34.1
>
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