selinux: change the handling of unknown classes

If allow_unknown==deny, SELinux treats an undefined kernel security
class as an error condition rather than as a typical permission denial
and thus does not allow permissions on undefined classes even when in
permissive mode.  Change the SELinux logic so that this case is handled
as a typical permission denial, subject to the usual permissive mode and
permissive domain handling.

Also drop the 'requested' argument from security_compute_av() and
helpers as it is a legacy of the original security server interface and
is unused.

Changes:
- Handle permissive domains consistently by moving up the test for a
permissive domain.
- Make security_compute_av_user() consistent with security_compute_av();
the only difference now is that security_compute_av() performs mapping
between the kernel-private class and permission indices and the policy
values.  In the userspace case, this mapping is handled by libselinux.
- Moved avd_init inside the policy lock.

Based in part on a patch by Paul Moore <paul.moore@hp.com>.

Reported-by: Andrew Worsley <amworsley@gmail.com>
Signed-off-by:  Stephen D. Smalley <sds@tycho.nsa.gov>
Reviewed-by: Paul Moore <paul.moore@hp.com>
Signed-off-by: James Morris <jmorris@namei.org>

security/selinux/include/security.h

@@ -96,13 +96,11 @@ struct av_decision {
 /* definitions of av_decision.flags */
 #define AVD_FLAGS_PERMISSIVE	0x0001
 
-int security_compute_av(u32 ssid, u32 tsid,
-			u16 tclass, u32 requested,
-			struct av_decision *avd);
+void security_compute_av(u32 ssid, u32 tsid,
+			 u16 tclass, struct av_decision *avd);
 
-int security_compute_av_user(u32 ssid, u32 tsid,
-			     u16 tclass, u32 requested,
-			     struct av_decision *avd);
+void security_compute_av_user(u32 ssid, u32 tsid,
+			     u16 tclass, struct av_decision *avd);
 
 int security_transition_sid(u32 ssid, u32 tsid,
 			    u16 tclass, u32 *out_sid);