Unable to open HID device in android (SELinux prevents it)

[tpkarras]

Hi. I'm new to hidapi so please forgive me.

I'm trying to open an input device in hidapi so I can change a setting that goes 1 or 0. I got it to attempt to open a device but pesky SELinux is preventing the device from being opened.

2022-10-09 13:14:38.030 29678-29678/com.openrearultra I/m.openrearultra: type=1400 audit(0.0:2672): avc: denied { read } for name="usb" dev="tmpfs" ino=17549 scontext=u:r:untrusted_app:s0:c146,c257,c512,c768 tcontext=u:object_r:usb_device:s0 tclass=dir permissive=1 app=com.openrearultra 2022-10-09 13:14:38.030 29678-29678/com.openrearultra I/m.openrearultra: type=1400 audit(0.0:2673): avc: denied { open } for path="/dev/bus/usb" dev="tmpfs" ino=17549 scontext=u:r:untrusted_app:s0:c146,c257,c512,c768 tcontext=u:object_r:usb_device:s0 tclass=dir permissive=1 app=com.openrearultra 2022-10-09 13:14:38.030 29678-29678/com.openrearultra I/m.openrearultra: type=1400 audit(0.0:2674): avc: denied { read } for name="devices" dev="sysfs" ino=56340 scontext=u:r:untrusted_app:s0:c146,c257,c512,c768 tcontext=u:object_r:sysfs:s0 tclass=dir permissive=1 app=com.openrearultra 2022-10-09 13:14:38.030 29678-29678/com.openrearultra I/m.openrearultra: type=1400 audit(0.0:2675): avc: denied { open } for path="/sys/bus/usb/devices" dev="sysfs" ino=56340 scontext=u:r:untrusted_app:s0:c146,c257,c512,c768 tcontext=u:object_r:sysfs:s0 tclass=dir permissive=1 app=com.openrearultra 2022-10-09 13:14:38.030 29678-29678/com.openrearultra I/m.openrearultra: type=1400 audit(0.0:2676): avc: denied { read } for name="busnum" dev="sysfs" ino=70076 scontext=u:r:untrusted_app:s0:c146,c257,c512,c768 tcontext=u:object_r:sysfs:s0 tclass=file permissive=1 app=com.openrearultra

yes... I'm using SELinux in permissive mode and got ro.debuggable set to 1.

is there anyway through the HID or I2C interface that I can access and change this setting. right now this is frustrating.

[Youw]

is there anyway through the HID or I2C interface...

Interesting why you've mentioned I2C. Your device is a USB device, and HIDAPI only supports LIBUSB on Android.

Accessing a USB devices on Android is a known generic "issue". LIBUSB cannot access those directly like on other *nix platforms.
Take a look in details here: https://github.com/libusb/libusb/wiki/Android

TL;DR

Try android/UsbManager + hid_libusb_wrap_sys_device.

[tpkarras]

It's an internal input device though. I'm trying to change a touchscreen device wake setting that's not visible through UsbManager and only visible through InputManager.

the touchscreen has an I2C driver but I don't know where to look.

if InputManager has a way of getting the file descriptor it'd be easy but alas. I'm stuck.

any ideas?

[Youw]

not visible through UsbManager

So your device is not visible over android/UsbManager, but visible over HIDAPI?

[tpkarras]

I'm using the vendor and product IDs provided by InputDevice

[tpkarras]

update: rebuilt the library the proper way. still no luck. SELinux enforcement is disabled but when trying to open it, there's no pointer referring to the USB object, it's just a null reference.

Any advice would be appreciated in proper operation of HIDAPI.

[Youw]

Share the sample of C and Java code related to your HID device handling, if you want more detailed advice.

[tpkarras]

Okay. Here's some Java code (since I'm not using any C code).

I'm using JNA to reflect from the hidapi shared object, this is what I have for the function in my interface according to what HIDAPI's guide gives me.

Pointer hid_open (short VID, short PID, Character serial);

hid_open works (cause I can see the SELinux messages about accessing USB devices) but I don't know if it's a permission issue or something else entirely that's causing it to return null.

this is the code I have that takes an InputDevice's Product ID and Vendor ID and uses it to open an hidapi instance to the device. (in this case, an internal Cypress touch controller)

short vid = (short)inputDevice.getVendorId(); short pid = (short)inputDevice.getProductId(); Pointer HIDDevice = HIDInterface.INSTANCE.hid_open(vid, pid, null);

Thanks for taking the time to help out, any solution provided would be helpful.

[Youw]

That's what I was trying to say in my first answer: hid_open will not work on Android.

What you need to do:

1. Get Android permission to open your USB device of interest:

    usbManager = (UsbManager) getSystemService(Context.USB_SERVICE);
    HashMap<String, UsbDevice> deviceList = usbManager.getDeviceList();
    for (UsbDevice usbDevice : deviceList.values()) {
        usbManager.requestPermission(usbDevice, mPermissionIntent);
    }

2. Open that device (if user has granted the permission):

    UsbDeviceConnection usbDeviceConnection = usbManager.openDevice(camDevice);
    int fileDescriptor = usbDeviceConnection.getFileDescriptor();

3. Open the device using hid_libusb_wrap_sys_device:

    Pointer HIDDevice = HIDInterface.INSTANCE.hid_libusb_wrap_sys_device(fileDescriptor, -1);

[Youw]

P.S.: (modified) sample is taken from here: https://github.com/libusb/libusb/blob/master/android/README