[libcamera-devel] [PATCH] android: Protect against null callbacks

[Umang Jain]

Hi Laurent,

On 9/8/20 1:24 PM, Laurent Pinchart wrote:
> According to the Android camera HAL C interface documentation, the
> camera service is supposed to set callbacks after initializing the HAL
> and calling get_number_of_cameras(), before any other calls to the
> module. We rely on this behaviour and use callbacks unconditionally,
> which would lead to a crash if the camera service behaved incorrectly.
>
> While the camera service isn't supposed to behave incorrectly,
> gracefully handling the error when opening cameras isn't costly, and
> provides better diagnostic than a crash.
>
> While at it, removed an unneeded [[maybe_unused]] attribute.
>
> Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
First of all,

Reviewed-by: Umang Jain <email at uajain.com>
> ---
>   src/android/camera3_hal.cpp        | 2 +-
>   src/android/camera_hal_manager.cpp | 7 ++++++-
>   2 files changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/src/android/camera3_hal.cpp b/src/android/camera3_hal.cpp
> index 67a497b8c829..d6e04af21470 100644
> --- a/src/android/camera3_hal.cpp
> +++ b/src/android/camera3_hal.cpp
> @@ -32,7 +32,7 @@ static int hal_get_camera_info(int id, struct camera_info *info)
>   	return cameraManager.getCameraInfo(id, info);
>   }
>   
> -static int hal_set_callbacks([[maybe_unused]] const camera_module_callbacks_t *callbacks)
> +static int hal_set_callbacks(const camera_module_callbacks_t *callbacks)
>   {
>   	cameraManager.setCallbacks(callbacks);
>   
> diff --git a/src/android/camera_hal_manager.cpp b/src/android/camera_hal_manager.cpp
> index a1805ebccf24..05b474010b1d 100644
> --- a/src/android/camera_hal_manager.cpp
> +++ b/src/android/camera_hal_manager.cpp
> @@ -29,7 +29,7 @@ LOG_DECLARE_CATEGORY(HAL);
>    */
>   
>   CameraHalManager::CameraHalManager()
> -	: cameraManager_(nullptr), numInternalCameras_(0),
> +	: cameraManager_(nullptr), callbacks_(nullptr), numInternalCameras_(0),
>   	  nextExternalCameraId_(firstExternalCameraId_)
>   {
>   }
> @@ -70,6 +70,11 @@ CameraDevice *CameraHalManager::open(unsigned int id,
>   {
>   	MutexLocker locker(mutex_);
>   
> +	if (!callbacks_) {
> +		LOG(HAL, Error) << "Can't open camera before callbacks are set";
> +		return nullptr;
> +	}
> +
At any point in time, were you able to trigger a crash to which, as a 
result, is this patch came into existence? Just curious.
>   	CameraDevice *camera = cameraDeviceFromHalId(id);
>   	if (!camera) {
>   		LOG(HAL, Error) << "Invalid camera id '" << id << "'";