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, 25 insertions, 7 deletions

diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
index 185f849..2ea108c 100644
--- a/security/selinux/ss/services.c
+++ b/security/selinux/ss/services.c
@@ -1389,6 +1389,7 @@ static int security_compute_sid(u32 ssid,
 				u32 *out_sid,
 				bool kern)
 {
+	struct class_datum *cladatum = NULL;
 	struct context *scontext = NULL, *tcontext = NULL, newcontext;
 	struct role_trans *roletr = NULL;
 	struct avtab_key avkey;
@@ -1437,12 +1438,20 @@ static int security_compute_sid(u32 ssid,
 		goto out_unlock;
 	}
 
+	if (tclass && tclass <= policydb.p_classes.nprim)
+		cladatum = policydb.class_val_to_struct[tclass - 1];
+
 	/* Set the user identity. */
 	switch (specified) {
 	case AVTAB_TRANSITION:
 	case AVTAB_CHANGE:
-		/* Use the process user identity. */
-		newcontext.user = scontext->user;
+		if (cladatum && cladatum->default_user == DEFAULT_TARGET) {
+			newcontext.user = tcontext->user;
+		} else {
+			/* notice this gets both DEFAULT_SOURCE and unset */
+			/* Use the process user identity. */
+			newcontext.user = scontext->user;
+		}
 		break;
 	case AVTAB_MEMBER:
 		/* Use the related object owner. */
@@ -1450,14 +1459,23 @@ static int security_compute_sid(u32 ssid,
 		break;
 	}
 
-	/* Set the role and type to default values. */
-	if ((tclass == policydb.process_class) || (sock == true)) {
-		/* Use the current role and type of process. */
+	/* Set the role to default values. */
+	if (cladatum && cladatum->default_role == DEFAULT_SOURCE) {
 		newcontext.role = scontext->role;
+	} else if (cladatum && cladatum->default_role == DEFAULT_TARGET) {
+		newcontext.role = tcontext->role;
+	} else {
+		if ((tclass == policydb.process_class) || (sock == true))
+			newcontext.role = scontext->role;
+		else
+			newcontext.role = OBJECT_R_VAL;
+	}
+
+	/* Set the type to default values. */
+	if ((tclass == policydb.process_class) || (sock == true)) {
+		/* Use the type of process. */
 		newcontext.type = scontext->type;
 	} else {
-		/* Use the well-defined object role. */
-		newcontext.role = OBJECT_R_VAL;
 		/* Use the type of the related object. */
 		newcontext.type = tcontext->type;
 	}