Ensure correct monolithic binary policy is loaded

When building a monolithic policy with 'make load', the
selinux_config(5) file 'SELINUXTYPE' entry determines what policy
is loaded as load_policy(8) does not take a path value (it always loads
the active system policy as defined by /etc/selinux/config).

Currently it is possible to load the wrong binary policy, for example if
the Reference Policy source is located at:
/etc/selinux/refpolicy
and the /etc/selinux/config file has the following entry:
SELINUXTYPE=targeted
Then the /etc/selinux/targeted/policy/policy.<ver> is loaded when
'make load' is executed.
Resolve this by using selinux_binary_policy_path(3) to determine the
current configured policy name and its location.

Another example is that if the Reference Policy source is located at:
/tmp/custom-rootfs/etc/selinux/refpolicy
and the /etc/selinux/config file has the following entry:
SELINUXTYPE=refpolicy
Then the /etc/selinux/refpolicy/policy/policy.<ver> is loaded when
'make DESTDIR=/tmp/custom-rootfs load' is executed (not the
/tmp/custom-rootfs/etc/selinux/refpolicy/policy/policy.<ver> that the
developer thought would be loaded).
Resolve this by checking if DESTDIR has been set.

Remove the '@touch $(tmpdir)/load' line as the file is never referenced.

Signed-off-by: Richard Haines <richard_c_haines@btinternet.com>

Makefile

@@ -97,6 +97,7 @@ genxml := $(PYTHON) $(support)/segenxml.py
 gendoc := $(PYTHON) $(support)/sedoctool.py
 genperm := $(PYTHON) $(support)/genclassperms.py
 policyvers := $(PYTHON) $(support)/policyvers.py
+binary_policy_path := $(PYTHON) $(support)/selinux_binary_policy_path.py
 fcsort := $(PYTHON) $(support)/fc_sort.py
 setbools := $(AWK) -f $(support)/set_bools_tuns.awk
 get_type_attr_decl := $(SED) -r -f $(support)/get_type_attr_decl.sed

Rules.monolithic

@@ -13,6 +13,12 @@ ifeq "$(kv)" ""
 	kv := $(pv)
 endif
 
+# load_policy(8) loads policy from /etc/selinux/<SELINUXTYPE>/policy/policy.$(pv)
+# It does this by reading the /etc/selinux/config file SELINUXTYPE entry to
+# form the full path. $(polbinpath) will contain this evaluated path for use as
+# a validation check.
+polbinpath := $(shell $(binary_policy_path))
+
 policy_conf = $(builddir)policy.conf
 fc = $(builddir)file_contexts
 polver = $(builddir)policy.$(pv)
@@ -91,9 +97,16 @@ endif
 # Load the binary policy
 #
 reload $(tmpdir)/load: $(loadpath) $(fcpath) $(appfiles)
+ifneq ($(DESTDIR),)
+	$(error Cannot load policy as '$$DESTDIR' is set to $(DESTDIR), \
+		creating an invalid policy load path)
+endif
+ifneq ($(polbinpath).$(pv),$(loadpath))
+	$(error Cannot load policy as invalid policy path: $(polbinpath).$(pv) - \
+		Check $(topdir)/config file entry is: "SELINUXTYPE=$(NAME)")
+endif
 	@echo "Loading $(NAME) $(loadpath)"
 	$(verbose) $(LOADPOLICY) -q $(loadpath)
-	@touch $(tmpdir)/load
 
 ########################################
 #

support/selinux_binary_policy_path.py

@@ -0,0 +1,12 @@
+#!/usr/bin/env python3
+
+try:
+    import warnings
+    with warnings.catch_warnings():
+        warnings.filterwarnings("ignore", category=PendingDeprecationWarning)
+        import selinux
+
+    if selinux.is_selinux_enabled():
+        print(selinux.selinux_binary_policy_path())
+except ImportError:
+    exit(0)