Add sysfs_batteryinfo label.

Shell user needs to be able to get current device battery_level via
/sys/class/power_supply/battery/capacity.  Create a global label and
corresponding policy for accessing this.  Rely on each device to label
the appropriate sysfs entry.

Bug: 26219114
Change-Id: I2c5ef489a9db2fdf7bbd5afd04278214b814351c

file.te

@@ -22,6 +22,7 @@ type selinuxfs, fs_type, mlstrustedobject;
 type cgroup, fs_type, mlstrustedobject;
 type sysfs, fs_type, sysfs_type, mlstrustedobject;
 type sysfs_writable, fs_type, sysfs_type, mlstrustedobject;
+type sysfs_batteryinfo, fs_type, sysfs_type;
 type sysfs_bluetooth_writable, fs_type, sysfs_type, mlstrustedobject;
 type sysfs_nfc_power_writable, fs_type, sysfs_type, mlstrustedobject;
 type sysfs_wake_lock, fs_type, sysfs_type;

healthd.te

@@ -16,6 +16,8 @@ binder_call(healthd, system_server)
 # TODO:  Split into a separate type?
 allow healthd sysfs:file write;
 
+allow healthd sysfs_batteryinfo:file r_file_perms;
+
 ###
 ### healthd: charger mode
 ###

shell.te

@@ -119,6 +119,8 @@ allow shell bootchart_data_file:file create_file_perms;
 # Make sure strace works for the non-privileged shell user
 allow shell self:process ptrace;
 
+# allow shell to get battery info
+allow shell sysfs_batteryinfo:file r_file_perms;
 
 # Allow access to ion memory allocation device.
 allow shell ion_device:chr_file rw_file_perms;