af_rxrpc: Fix XDR length check in rxrpc key demarshalling.

There may be padding on the ticket contained in the key payload, so just ensure
that the claimed token length is large enough, rather than exactly the right
size.
Signed-off-by: NNathaniel Wesley Filardo <nwf@cs.jhu.edu>
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/rxrpc/ar-key.c

@@ -99,7 +99,7 @@ static int rxrpc_instantiate_xdr_rxkad(struct key *key, const __be32 *xdr,
 	_debug("tktlen: %x", tktlen);
 	if (tktlen > AFSTOKEN_RK_TIX_MAX)
 		return -EKEYREJECTED;
-	if (8 * 4 + tktlen != toklen)
+	if (toklen < 8 * 4 + tktlen)
 		return -EKEYREJECTED;
 
 	plen = sizeof(*token) + sizeof(*token->kad) + tktlen;