Add a new context for property ota.warm_reset

The property is set to inform kernel to do a warm_reset on the next
reboot. This is useful to persist the logs to debug device boot
failures. More details in http://go/rvc-ota-persist-logs.

The property is set to 1 by update_engine after an OTA. And it's set to
0 by update_verifier or vold after we mark the current slot boot
successful.
The property is read by vendor_init. And according to its value,
vendor_init writes a particular sysfs file to schedule a warm reset
on the following reboot.

Without the new context, the denial message says:
[   13.423163] audit: type=1107 audit(1746393.166:8): pid=1 uid=0 auid=4294967295 ses=4294967295 subj=u:r:init:s0 msg='avc:  denied  { read } for property=ota.warm_reset pid=0 uid=0 gid=0 scontext=u:r:vendor_init:s0 tcontext=u:object_r:default_prop:s0 tclass=file permissive=0'
[   23.096497] init: Unable to set property 'OTA.warm_reset' from uid:0 gid:2001 pid:841: SELinux permission check failed
[   23.096574] type=1107 audit(1573768000.668:42): uid=0 auid=4294967295 ses=4294967295 subj=u:r:init:s0 msg='avc: denied { set } for property=OTA.warm_reset pid=841 uid=0 gid=2001 scontext=u:r:update_verifier:s0 tcontext=u:object_r:default_prop:s0 tclass=property_service permissive=0'
[   23.108430] update_verifier: Failed to reset the warm reset flag

Bug: 143489994
Test: check the property can be set by update_engine, and read by vendor_init
Change-Id: I87c12a53a138b72ecfed3ab6a4d846c20f5a8484
7 files changed