Bluetooth: Add streaming mode receive and incoming packet classifier

Streaming mode reception is fairly simple, with in-sequence frames
being reassembled as they arrive.  Out-of-sequence frames are dropped,
and also clear any partially-assembled SDUs that may exist.

The packet classifier determines if the txseq value of the incoming
packet is expected, invalid (resulting in a disconnection), invalid
(ignorable), duplicate, or having to do with an SREJ request that was
previously sent.  The rules for each classification are defined in the
ERTM specification, and consolidating these rules in one place helps
clarify the receive state machine.
Signed-off-by: Mat Martineau <mathewm@codeaurora.org>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>

net/bluetooth/l2cap_core.c

@@ -2420,6 +2420,13 @@ static int l2cap_tx(struct l2cap_chan *chan, struct l2cap_ctrl *control,
 	return err;
 }
 
+static void l2cap_pass_to_tx(struct l2cap_chan *chan,
+			     struct l2cap_ctrl *control)
+{
+	BT_DBG("chan %p, control %p", chan, control);
+	l2cap_tx(chan, control, 0, L2CAP_EV_RECV_REQSEQ_AND_FBIT);
+}
+
 /* Copy frame to all raw sockets on that connection */
 static void l2cap_raw_recv(struct l2cap_conn *conn, struct sk_buff *skb)
 {
@@ -4324,11 +4331,12 @@ static void append_skb_frag(struct sk_buff *skb,
 	skb->truesize += new_frag->truesize;
 }
 
-static int l2cap_reassemble_sdu(struct l2cap_chan *chan, struct sk_buff *skb, u32 control)
+static int l2cap_reassemble_sdu(struct l2cap_chan *chan, struct sk_buff *skb,
+				struct l2cap_ctrl *control)
 {
 	int err = -EINVAL;
 
-	switch (__get_ctrl_sar(chan, control)) {
+	switch (control->sar) {
 	case L2CAP_SAR_UNSEGMENTED:
 		if (chan->sdu)
 			break;
@@ -4463,7 +4471,6 @@ static void l2cap_check_srej_gap(struct l2cap_chan *chan, u16 tx_seq)
 
 		skb = skb_dequeue(&chan->srej_q);
 		control = __set_ctrl_sar(chan, bt_cb(skb)->control.sar);
-		err = l2cap_reassemble_sdu(chan, skb, control);
 
 		if (err < 0) {
 			l2cap_send_disconn_req(chan->conn, chan, ECONNRESET);
@@ -4637,7 +4644,6 @@ static inline int l2cap_data_channel_iframe(struct l2cap_chan *chan, u32 rx_cont
 		return 0;
 	}
 
-	err = l2cap_reassemble_sdu(chan, skb, rx_control);
 	chan->buffer_seq = __next_seq(chan, chan->buffer_seq);
 
 	if (err < 0) {
@@ -4822,6 +4828,93 @@ static inline int l2cap_data_channel_sframe(struct l2cap_chan *chan, u32 rx_cont
 	return 0;
 }
 
+static u8 l2cap_classify_txseq(struct l2cap_chan *chan, u16 txseq)
+{
+	BT_DBG("chan %p, txseq %d", chan, txseq);
+
+	BT_DBG("last_acked_seq %d, expected_tx_seq %d", chan->last_acked_seq,
+	       chan->expected_tx_seq);
+
+	if (chan->rx_state == L2CAP_RX_STATE_SREJ_SENT) {
+		if (__seq_offset(chan, txseq, chan->last_acked_seq) >=
+								chan->tx_win) {
+			/* See notes below regarding "double poll" and
+			 * invalid packets.
+			 */
+			if (chan->tx_win <= ((chan->tx_win_max + 1) >> 1)) {
+				BT_DBG("Invalid/Ignore - after SREJ");
+				return L2CAP_TXSEQ_INVALID_IGNORE;
+			} else {
+				BT_DBG("Invalid - in window after SREJ sent");
+				return L2CAP_TXSEQ_INVALID;
+			}
+		}
+
+		if (chan->srej_list.head == txseq) {
+			BT_DBG("Expected SREJ");
+			return L2CAP_TXSEQ_EXPECTED_SREJ;
+		}
+
+		if (l2cap_ertm_seq_in_queue(&chan->srej_q, txseq)) {
+			BT_DBG("Duplicate SREJ - txseq already stored");
+			return L2CAP_TXSEQ_DUPLICATE_SREJ;
+		}
+
+		if (l2cap_seq_list_contains(&chan->srej_list, txseq)) {
+			BT_DBG("Unexpected SREJ - not requested");
+			return L2CAP_TXSEQ_UNEXPECTED_SREJ;
+		}
+	}
+
+	if (chan->expected_tx_seq == txseq) {
+		if (__seq_offset(chan, txseq, chan->last_acked_seq) >=
+		    chan->tx_win) {
+			BT_DBG("Invalid - txseq outside tx window");
+			return L2CAP_TXSEQ_INVALID;
+		} else {
+			BT_DBG("Expected");
+			return L2CAP_TXSEQ_EXPECTED;
+		}
+	}
+
+	if (__seq_offset(chan, txseq, chan->last_acked_seq) <
+		__seq_offset(chan, chan->expected_tx_seq,
+			     chan->last_acked_seq)){
+		BT_DBG("Duplicate - expected_tx_seq later than txseq");
+		return L2CAP_TXSEQ_DUPLICATE;
+	}
+
+	if (__seq_offset(chan, txseq, chan->last_acked_seq) >= chan->tx_win) {
+		/* A source of invalid packets is a "double poll" condition,
+		 * where delays cause us to send multiple poll packets.  If
+		 * the remote stack receives and processes both polls,
+		 * sequence numbers can wrap around in such a way that a
+		 * resent frame has a sequence number that looks like new data
+		 * with a sequence gap.  This would trigger an erroneous SREJ
+		 * request.
+		 *
+		 * Fortunately, this is impossible with a tx window that's
+		 * less than half of the maximum sequence number, which allows
+		 * invalid frames to be safely ignored.
+		 *
+		 * With tx window sizes greater than half of the tx window
+		 * maximum, the frame is invalid and cannot be ignored.  This
+		 * causes a disconnect.
+		 */
+
+		if (chan->tx_win <= ((chan->tx_win_max + 1) >> 1)) {
+			BT_DBG("Invalid/Ignore - txseq outside tx window");
+			return L2CAP_TXSEQ_INVALID_IGNORE;
+		} else {
+			BT_DBG("Invalid - txseq outside tx window");
+			return L2CAP_TXSEQ_INVALID;
+		}
+	} else {
+		BT_DBG("Unexpected - txseq indicates missing frames");
+		return L2CAP_TXSEQ_UNEXPECTED;
+	}
+}
+
 static int l2cap_rx(struct l2cap_chan *chan, struct l2cap_ctrl *control,
 		    struct sk_buff *skb, u8 event)
 {
@@ -4832,8 +4925,39 @@ static int l2cap_rx(struct l2cap_chan *chan, struct l2cap_ctrl *control,
 static int l2cap_stream_rx(struct l2cap_chan *chan, struct l2cap_ctrl *control,
 			   struct sk_buff *skb)
 {
-	/* Placeholder */
-	return -ENOTSUPP;
+	int err = 0;
+
+	BT_DBG("chan %p, control %p, skb %p, state %d", chan, control, skb,
+	       chan->rx_state);
+
+	if (l2cap_classify_txseq(chan, control->txseq) ==
+	    L2CAP_TXSEQ_EXPECTED) {
+		l2cap_pass_to_tx(chan, control);
+
+		BT_DBG("buffer_seq %d->%d", chan->buffer_seq,
+		       __next_seq(chan, chan->buffer_seq));
+
+		chan->buffer_seq = __next_seq(chan, chan->buffer_seq);
+
+		l2cap_reassemble_sdu(chan, skb, control);
+	} else {
+		if (chan->sdu) {
+			kfree_skb(chan->sdu);
+			chan->sdu = NULL;
+		}
+		chan->sdu_last_frag = NULL;
+		chan->sdu_len = 0;
+
+		if (skb) {
+			BT_DBG("Freeing %p", skb);
+			kfree_skb(skb);
+		}
+	}
+
+	chan->last_acked_seq = control->txseq;
+	chan->expected_tx_seq = __next_seq(chan, control->txseq);
+
+	return err;
 }
 
 static int l2cap_data_rcv(struct l2cap_chan *chan, struct sk_buff *skb)