dtls-window.c

/*
 * DTLS sliding window handling
 */
#define DTLS_EPOCH_SHIFT		(6 * CHAR_BIT)
#define DTLS_SEQ_NUM_MASK		0x0000FFFFFFFFFFFFL

#define DTLS_WINDOW_INIT(W)		((W).bits = (W.start) = 0)

#define DTLS_SAME_EPOCH(S1, S2)		(((S1) >> DTLS_EPOCH_SHIFT) \
					== ((S2) >> DTLS_EPOCH_SHIFT))

/* This check cannot handle the case of a freshly initialized sliding
 * window, and a packet with sequence nr of 0 being received. However,
 * since in TLS the first encrypted packet sent, is the Finished one,
 * we never trigger that issue.
*/
#define DTLS_WINDOW_INSIDE(W, S) ((((S) & DTLS_SEQ_NUM_MASK) > (W).start) && \
					(((S)  & DTLS_SEQ_NUM_MASK) - \
						(W).start <= \
						(sizeof((W).bits) * CHAR_BIT)))

#define DTLS_WINDOW_OFFSET(W, S)  ((((S) & DTLS_SEQ_NUM_MASK) - (W).start) - 1)

#define DTLS_WINDOW_RECEIVED(W, S) (((W).bits & ((u64)1 << \
				     DTLS_WINDOW_OFFSET(W, S))) != 0)

#define DTLS_WINDOW_MARK(W, S) ((W).bits |= ((u64)1 << \
					     DTLS_WINDOW_OFFSET(W, S)))

#define DTLS_WINDOW_UPDATE(W)		\
					if (((W).bits & 0xffffffffffff0000LL) != 0) { \
						(W).bits = (W).bits >> 1; \
						(W).start++; \
					} \
					while ((W).bits & (u64)1) {	\
						(W).bits = (W).bits >> 1; \
						(W).start++; \
					}

/* Handle DTLS sliding window
 * rv: rv < 0  drop packet
 *     rv == 0 OK
 */
static int dtls_window(struct tls_sock *tsk, const char *sn)
{
	__be64 *seq_num_ptr, *seq_num_last_ptr;
	u64 seq_num, seq_num_last;

	seq_num_ptr = (__be64 *)sn;
	seq_num_last_ptr = (__be64 *)tsk->iv_recv;

	seq_num = be64_to_cpu(*seq_num_ptr);
	seq_num_last = be64_to_cpu(*seq_num_last_ptr);

	if (!DTLS_SAME_EPOCH(seq_num_last, seq_num))
		return -1;

	/* are we inside sliding window? */
	if (!DTLS_WINDOW_INSIDE(tsk->dtls_window, seq_num))
		return -2;

	/* already received? */
	if (DTLS_WINDOW_RECEIVED(tsk->dtls_window, seq_num))
		return -3;

	DTLS_WINDOW_MARK(tsk->dtls_window, seq_num);
	DTLS_WINDOW_UPDATE(tsk->dtls_window);

	return 0;
}