SELinux: allow default source/target selectors for user/role/range

When new objects are created we have great and flexible rules to
determine the type of the new object.  We aren't quite as flexible or
mature when it comes to determining the user, role, and range.  This
patch adds a new ability to specify the place a new objects user, role,
and range should come from.  For users and roles it can come from either
the source or the target of the operation.  aka for files the user can
either come from the source (the running process and todays default) or
it can come from the target (aka the parent directory of the new file)

examples always are done with
directory context: system_u:object_r:mnt_t:s0-s0:c0.c512
process context: unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023

[no rule]
	unconfined_u:object_r:mnt_t:s0   test_none
[default user source]
	unconfined_u:object_r:mnt_t:s0   test_user_source
[default user target]
	system_u:object_r:mnt_t:s0       test_user_target
[default role source]
	unconfined_u:unconfined_r:mnt_t:s0 test_role_source
[default role target]
	unconfined_u:object_r:mnt_t:s0   test_role_target
[default range source low]
	unconfined_u:object_r:mnt_t:s0 test_range_source_low
[default range source high]
	unconfined_u:object_r:mnt_t:s0:c0.c1023 test_range_source_high
[default range source low-high]
	unconfined_u:object_r:mnt_t:s0-s0:c0.c1023 test_range_source_low-high
[default range target low]
	unconfined_u:object_r:mnt_t:s0 test_range_target_low
[default range target high]
	unconfined_u:object_r:mnt_t:s0:c0.c512 test_range_target_high
[default range target low-high]
	unconfined_u:object_r:mnt_t:s0-s0:c0.c512 test_range_target_low-high

Signed-off-by: Eric Paris <eparis@redhat.com>

1 files changed, 24 insertions, 0 deletions

diff --git a/security/selinux/ss/mls.c b/security/selinux/ss/mls.c
index fbf9c5816c71..40de8d3f208e 100644
--- a/security/selinux/ss/mls.c
+++ b/security/selinux/ss/mls.c
@@ -517,6 +517,8 @@ int mls_compute_sid(struct context *scontext,
 {
 	struct range_trans rtr;
 	struct mls_range *r;
+	struct class_datum *cladatum;
+	int default_range = 0;
 
 	if (!policydb.mls_enabled)
 		return 0;
@@ -530,6 +532,28 @@ int mls_compute_sid(struct context *scontext,
 		r = hashtab_search(policydb.range_tr, &rtr);
 		if (r)
 			return mls_range_set(newcontext, r);
+
+		if (tclass && tclass <= policydb.p_classes.nprim) {
+			cladatum = policydb.class_val_to_struct[tclass - 1];
+			if (cladatum)
+				default_range = cladatum->default_range;
+		}
+
+		switch (default_range) {
+		case DEFAULT_SOURCE_LOW:
+			return mls_context_cpy_low(newcontext, scontext);
+		case DEFAULT_SOURCE_HIGH:
+			return mls_context_cpy_high(newcontext, scontext);
+		case DEFAULT_SOURCE_LOW_HIGH:
+			return mls_context_cpy(newcontext, scontext);
+		case DEFAULT_TARGET_LOW:
+			return mls_context_cpy_low(newcontext, tcontext);
+		case DEFAULT_TARGET_HIGH:
+			return mls_context_cpy_high(newcontext, tcontext);
+		case DEFAULT_TARGET_LOW_HIGH:
+			return mls_context_cpy(newcontext, tcontext);
+		}
+
 		/* Fallthrough */
 	case AVTAB_CHANGE:
 		if ((tclass == policydb.process_class) || (sock == true))