Allow access to sysfs usb nodes.

Some legitimate functionality currently requires direct sysfs access
that is not otherwise possible via the android APIs.  Specifically,
isochronous USB transfers require this direct access, without which USB
audio applications would noticibly suffer.

Grant read access to the usb files under /sys/devices to prevent this
regression.

Bug: 28417852
Change-Id: I3424bf3498ffa0eb647a54cc962ab8c54f291728

domain.te

@@ -110,6 +110,8 @@ r_dir_file(domain, zoneinfo_data_file)
 # Lots of processes access current CPU information
 r_dir_file(domain, sysfs_devices_system_cpu)
 
+r_dir_file(domain, sysfs_usb);
+
 # files under /data.
 allow domain system_data_file:dir { search getattr };
 allow domain system_data_file:lnk_file read;

file.te

@@ -30,6 +30,7 @@ type sysfs_hwrandom, fs_type, sysfs_type;
 type sysfs_nfc_power_writable, fs_type, sysfs_type, mlstrustedobject;
 type sysfs_wake_lock, fs_type, sysfs_type;
 type sysfs_mac_address, fs_type, sysfs_type;
+type sysfs_usb, sysfs_type, file_type, mlstrustedobject;
 type configfs, fs_type;
 # /sys/devices/system/cpu
 type sysfs_devices_system_cpu, fs_type, sysfs_type;