enabled /sbin/modprobe for recovery mode

This change defines new policy for modprobe (/sbin/modprobe) that should
be used in both recovery and android mode.

Denials:
[   16.986440] c0    437 audit: type=1400 audit(6138546.943:5): avc:
denied  { read } for  pid=437 comm="modprobe" name="modules" dev="proc"
ino=4026532405 scontext=u:object_r:modprobe:s0
tcontext=u:object_r:proc:s0 tclass=file permissive=1
[   16.986521] c0    437 audit: type=1400 audit(6138546.943:6): avc:
denied  { open } for  pid=437 comm="modprobe" path="/proc/modules"
dev="proc" ino=4026532405 scontext=u:object_r:modprobe:s0
tcontext=u:object_r:proc:s0 tclass=file permissive=1
[   16.986544] c0    437 audit: type=1400 audit(6138546.943:7): avc:
denied  { getattr } for  pid=437 comm="modprobe" path="/proc/modules"
dev="proc" ino=4026532405 scontext=u:object_r:modprobe:s0
tcontext=u:object_r:proc:s0 tclass=file permissive=1

Bug: 35633646
Test: Build and tested it works in sailfish recovery. The modprobe is
invoked in init.rc (at the end of 'on init') with following command line

    exec u:r:modprobe:s0 -- /sbin/modprobe -a nilfs2 ftl

Change-Id: Ie70be6f918bea6059f806e2eb38cd48229facafa

private/file_contexts

@@ -18,6 +18,9 @@
 /init               u:object_r:init_exec:s0
 /sbin(/.*)?         u:object_r:rootfs:s0
 
+# For kernel modules
+/lib(/.*)?          u:object_r:rootfs:s0
+
 # Empty directories
 /lost\+found        u:object_r:rootfs:s0
 /acct               u:object_r:cgroup:s0

private/genfs_contexts

@@ -7,6 +7,7 @@ genfscon proc /interrupts u:object_r:proc_interrupts:s0
 genfscon proc /iomem u:object_r:proc_iomem:s0
 genfscon proc /meminfo u:object_r:proc_meminfo:s0
 genfscon proc /misc u:object_r:proc_misc:s0
+genfscon proc /modules u:object_r:proc_modules:s0
 genfscon proc /net u:object_r:proc_net:s0
 genfscon proc /net/xt_qtaguid/ctrl u:object_r:qtaguid_proc:s0
 genfscon proc /cpuinfo u:object_r:proc_cpuinfo:s0

private/init.te

@@ -13,6 +13,7 @@ recovery_only(`
 domain_trans(init, shell_exec, shell)
 domain_trans(init, init_exec, ueventd)
 domain_trans(init, init_exec, watchdogd)
+domain_trans(init, rootfs, modprobe)
 # case where logpersistd is actually logcat -f in logd context (nee: logcatd)
 userdebug_or_eng(`
   domain_auto_trans(init, logcat_exec, logpersist)

public/file.te

@@ -17,6 +17,7 @@ type proc_interrupts, fs_type;
 type proc_iomem, fs_type;
 type proc_meminfo, fs_type;
 type proc_misc, fs_type;
+type proc_modules, fs_type;
 type proc_net, fs_type;
 type proc_perf, fs_type;
 type proc_stat, fs_type;

public/modprobe.te

+type modprobe, domain;
+
+allow modprobe proc_modules:file r_file_perms;
+allow modprobe self:capability sys_module;
+recovery_only(`
+  allow modprobe rootfs:system module_load;
+  allow modprobe rootfs:file r_file_perms;
+')