allow init and system_server access to tracing

Revise policy, to allow init and system_server to configure,
clear, and read kernel trace events. This will enable us to
debug certain WiFi failures.

Note that system_server is restricted to only accessing
a wifi-specific trace instance. (Hence, system_server is
not allowed to interfere with atrace.) Moreover, even for
the wifi trace instance, system_server is granted limited
permissions. (system_server can not, e.g., change which
events are traced.)

Note also that init and system_server are only granted these
powers on userdebug or eng builds.

The init.te and system_server.te changes resolve the
following denials:

// Denials when wifi-events.rc configures tracing
{ write } for pid=1 comm="init" name="instances" dev="debugfs" ino=755 scontext=u:r:init:s0 tcontext=u:object_r:debugfs_tracing_instances:s0 tclass=dir permissive=1
{ add_name } for pid=1 comm="init" name="wifi" scontext=u:r:init:s0 tcontext=u:object_r:debugfs_tracing_instances:s0 tclass=dir permissive=1
{ create } for pid=1 comm="init" name="wifi" scontext=u:r:init:s0 tcontext=u:object_r:debugfs_tracing_instances:s0 tclass=dir permissive=1
{ write } for pid=1 comm="init" name="tracing_on" dev="debugfs" ino=18067 scontext=u:r:init:s0 tcontext=u:object_r:debugfs_wifi_tracing:s0 tclass=file permissive=1
{ write } for pid=1 comm="init" name="buffer_size_kb" dev="debugfs" ino=18061 scontext=u:r:init:s0 tcontext=u:object_r:debugfs_tracing_instances:s0 tclass=file permissive=1

// Denials when system_server sets up fail-safe
// (auto-terminate tracing if system_server dies)
{ search } for pid=882 comm="system_server" name="instances" dev="debugfs" ino=755 scontext=u:r:system_server:s0 tcontext=u:object_r:debugfs_tracing_instances:s0 tclass=dir permissive=1
{ read } for pid=882 comm="system_server" name="free_buffer" dev="debugfs" ino=18063 scontext=u:r:system_server:s0 tcontext=u:object_r:debugfs_wifi_tracing:s0 tclass=file permissive=1
{ open } for pid=882 comm="system_server" path="/sys/kernel/debug/tracing/instances/wifi/free_buffer" dev="debugfs" ino=18063 scontext=u:r:system_server:s0 tcontext=u:object_r:debugfs_wifi_tracing:s0 tclass=file permissive=1
{ getattr } for pid=882 comm="system_server" path="/sys/kernel/debug/tracing/instances/wifi/free_buffer" dev="debugfs" ino=18063 scontext=u:r:system_server:s0 tcontext=u:object_r:debugfs_wifi_tracing:s0 tclass=file permissive=1

// Denials when system_server toggles tracing on or off
// (WifiStateMachine is a thread in system_server)
{ search } for pid=989 comm="WifiStateMachin" name="instances" dev="debugfs" ino=755 scontext=u:r:system_server:s0 tcontext=u:object_r:debugfs_tracing_instances:s0 tclass=dir permissive=1
{ write } for pid=989 comm="WifiStateMachin" name="tracing_on" dev="debugfs" ino=18067 scontext=u:r:system_server:s0 tcontext=u:object_r:debugfs_wifi_tracing:s0 tclass=file permissive=1
{ open } for pid=989 comm="WifiStateMachin" path="/sys/kernel/debug/tracing/instances/wifi/tracing_on" dev="debugfs" ino=18067 scontext=u:r:system_server:s0 tcontext=u:object_r:debugfs_wifi_tracing:s0 tclass=file permissive=1
{ getattr } for pid=989 comm="WifiStateMachin" path="/sys/kernel/debug/tracing/instances/wifi/tracing_on" dev="debugfs" ino=18067 scontext=u:r:system_server:s0 tcontext=u:object_r:debugfs_wifi_tracing:s0 tclass=file permissive=1
{ write } for pid=989 comm="WifiStateMachin" name="tracing_on" dev="debugfs" ino=18067 scontext=u:r:system_server:s0 tcontext=u:object_r:debugfs_wifi_tracing:s0 tclass=file permissive=1
{ open } for pid=989 comm="WifiStateMachin" path="/sys/kernel/debug/tracing/instances/wifi/tracing_on" dev="debugfs" ino=18067 scontext=u:r:system_server:s0 tcontext=u:object_r:debugfs_wifi_tracing:s0 tclass=file permissive=1
{ getattr } for pid=989 comm="WifiStateMachin" path="/sys/kernel/debug/tracing/instances/wifi/tracing_on" dev="debugfs" ino=18067 scontext=u:r:system_server:s0 tcontext=u:object_r:debugfs_wifi_tracing:s0 tclass=file permissive=1

// Denials when system_server reads the event trace
// (This happens in response to a dumpsys request)
{ search } for pid=3537 comm="Binder:882_B" name="instances" dev="debugfs" ino=755 scontext=u:r:system_server:s0 tcontext=u:object_r:debugfs_tracing_instances:s0 tclass=dir permissive=1
{ read } for pid=3537 comm="Binder:882_B" name="trace" dev="debugfs" ino=18059 scontext=u:r:system_server:s0 tcontext=u:object_r:debugfs_wifi_tracing:s0 tclass=file permissive=1
{ open } for pid=3537 comm="Binder:882_B" path="/sys/kernel/debug/tracing/instances/wifi/trace" dev="debugfs" ino=18059 scontext=u:r:system_server:s0 tcontext=u:object_r:debugfs_wifi_tracing:s0 tclass=file permissive=1
{ getattr } for pid=3537 comm="Binder:882_B" path="/sys/kernel/debug/tracing/instances/wifi/trace" dev="debugfs" ino=18059 scontext=u:r:system_server:s0 tcontext=u:object_r:debugfs_wifi_tracing:s0 tclass=file permissive=1
{ write } for pid=3537 comm="Binder:882_B" name="trace" dev="debugfs" ino=18059 scontext=u:r:system_server:s0 tcontext=u:object_r:debugfs_wifi_tracing:s0 tclass=file permissive=1

Bug: 27254565
Test: manual
Manual test:
- Build this CL along with CL:322337
- Verify that system boots, and that we can connect to GoogleGuest.
  (Testing of actual trace functionality with require some more
  patches in frameworks/opt/net/wifi.)
$ adb root && adb shell dmesg | egrep 'avc: denied.+debugfs'

Change-Id: Ib6eb4116549277f85bd510d25fb30200f1752f4d

private/file_contexts

@@ -434,9 +434,13 @@
 #############################
 # debugfs files
 #
-/sys/kernel/debug/mmc0(/.*)?             u:object_r:debugfs_mmc:s0
-/sys/kernel/debug/tracing(/.*)?          u:object_r:debugfs_tracing:s0
-/sys/kernel/debug/tracing/trace_marker   u:object_r:debugfs_trace_marker:s0
+/sys/kernel/debug/mmc0(/.*)?                            u:object_r:debugfs_mmc:s0
+/sys/kernel/debug/tracing(/.*)?				u:object_r:debugfs_tracing:s0
+/sys/kernel/debug/tracing/trace_marker			u:object_r:debugfs_trace_marker:s0
+/sys/kernel/debug/tracing/instances(/.*)?		u:object_r:debugfs_tracing_instances:s0
+/sys/kernel/debug/tracing/instances/wifi/free_buffer	u:object_r:debugfs_wifi_tracing:s0
+/sys/kernel/debug/tracing/instances/wifi/trace		u:object_r:debugfs_wifi_tracing:s0
+/sys/kernel/debug/tracing/instances/wifi/tracing_on	u:object_r:debugfs_wifi_tracing:s0
 
 #############################
 # asec containers

public/file.te

@@ -62,6 +62,8 @@ type debugfs, fs_type;
 type debugfs_mmc, fs_type, debugfs_type;
 type debugfs_trace_marker, fs_type, debugfs_type, mlstrustedobject;
 type debugfs_tracing, fs_type, debugfs_type;
+type debugfs_tracing_instances, fs_type, debugfs_type;
+type debugfs_wifi_tracing, fs_type, debugfs_type;
 type pstorefs, fs_type;
 type functionfs, fs_type, mlstrustedobject;
 type oemfs, fs_type, contextmount_type;

public/init.te

@@ -180,6 +180,13 @@ allow init dev_type:lnk_file create;
 # Disable tracing by writing to /sys/kernel/debug/tracing/tracing_on
 allow init debugfs_tracing:file w_file_perms;
 
+userdebug_or_eng(`
+  # Setup and control wifi event tracing (see wifi-events.rc)
+  allow init debugfs_tracing_instances:dir create_dir_perms;
+  allow init debugfs_tracing_instances:file w_file_perms;
+  allow init debugfs_wifi_tracing:file w_file_perms;
+')
+
 # chown/chmod on pseudo files.
 allow init { fs_type -contextmount_type -sdcard_type -rootfs }:file { open read setattr };
 allow init { fs_type -contextmount_type -sdcard_type -rootfs }:dir  { open read setattr search };

public/system_server.te

@@ -603,6 +603,12 @@ r_dir_file(system_server, sysfs_type)
 # Allow system_server to make binder calls to hwservicemanager
 binder_call(system_server, hwservicemanager)
 
+userdebug_or_eng(`
+  # Allow WifiService to start, stop, and read wifi-specific trace events.
+  allow system_server debugfs_tracing_instances:dir search;
+  allow system_server debugfs_wifi_tracing:file rw_file_perms;
+')
+
 ###
 ### Neverallow rules
 ###