KEYS: Add a new keyctl op to reject a key with a specified error code

Add a new keyctl op to reject a key with a specified error code.  This works
much the same as negating a key, and so keyctl_negate_key() is made a special
case of keyctl_reject_key().  The difference is that keyctl_negate_key()
selects ENOKEY as the error to be reported.

Typically the key would be rejected with EKEYEXPIRED, EKEYREVOKED or
EKEYREJECTED, but this is not mandatory.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: James Morris <jmorris@namei.org>
diff --git a/security/keys/internal.h b/security/keys/internal.h
index a52aa7c..286c095 100644
--- a/security/keys/internal.h
+++ b/security/keys/internal.h
@@ -214,6 +214,7 @@
 extern long keyctl_get_security(key_serial_t keyid, char __user *buffer,
 				size_t buflen);
 extern long keyctl_session_to_parent(void);
+extern long keyctl_reject_key(key_serial_t, unsigned, unsigned, key_serial_t);
 
 /*
  * Debugging key validation