system_writes_mnt_vendor_violators for device launched before P.

In cases when a device upgrades to system-as-root from O to P, it needs a mount
point for an already existing partition that is accessed by both system and
vendor.

Devices launching with P must not have /mnt/vendor accessible to system.

Bug: 78598545
Test: m selinx_policy
Change-Id: Ia7bcde44e2b8657a7ad9e0d9bae7a7259f40936f

public/attributes

@@ -184,6 +184,11 @@ expandattribute system_executes_vendor_violators false;
 attribute system_writes_vendor_properties_violators;
 expandattribute system_writes_vendor_properties_violators false;
 
+# All system domains which violate the requirement of not writing to
+# /mnt/vendor/*. Must not be used on devices launched with P or later.
+attribute system_writes_mnt_vendor_violators;
+expandattribute system_writes_mnt_vendor_violators false;
+
 # hwservices that are accessible from untrusted applications
 # WARNING: Use of this attribute should be avoided unless
 # absolutely necessary.  It is a temporary allowance to aid the

public/domain.te

@@ -1434,6 +1434,7 @@ neverallow {
   -init
   -ueventd
   -vold
+  -system_writes_mnt_vendor_violators
 } mnt_vendor_file:dir *;
 
 # Only apps are allowed access to vendor public libraries.