rxrpc: Fix missing security check on incoming calls

Fix rxrpc_new_incoming_call() to check that we have a suitable service key
available for the combination of service ID and security class of a new
incoming call - and to reject calls for which we don't.

This causes an assertion like the following to appear:

	rxrpc: Assertion failed - 6(0x6) == 12(0xc) is false
	kernel BUG at net/rxrpc/call_object.c:456!

Where call->state is RXRPC_CALL_SERVER_SECURING (6) rather than
RXRPC_CALL_COMPLETE (12).

Fixes: 248f219cb8bc ("rxrpc: Rewrite the data and ack handling code")
Reported-by: Marc Dionne <marc.dionne@auristor.com>
Signed-off-by: David Howells <dhowells@redhat.com>
diff --git a/net/rxrpc/rxkad.c b/net/rxrpc/rxkad.c
index 8d8aa3c..098f1f9 100644
--- a/net/rxrpc/rxkad.c
+++ b/net/rxrpc/rxkad.c
@@ -648,9 +648,9 @@ static int rxkad_issue_challenge(struct rxrpc_connection *conn)
 	u32 serial;
 	int ret;
 
-	_enter("{%d,%x}", conn->debug_id, key_serial(conn->params.key));
+	_enter("{%d,%x}", conn->debug_id, key_serial(conn->server_key));
 
-	ret = key_validate(conn->params.key);
+	ret = key_validate(conn->server_key);
 	if (ret < 0)
 		return ret;
 
@@ -1293,6 +1293,7 @@ static void rxkad_exit(void)
 const struct rxrpc_security rxkad = {
 	.name				= "rxkad",
 	.security_index			= RXRPC_SECURITY_RXKAD,
+	.no_key_abort			= RXKADUNKNOWNKEY,
 	.init				= rxkad_init,
 	.exit				= rxkad_exit,
 	.init_connection_security	= rxkad_init_connection_security,