Bluetooth: Add backlog queue to ERTM code

backlog queue is the canonical mechanism to avoid race conditions due
interrupts in bottom half context. After the socket lock is released the
net core take care of push all skb in its backlog queue.

Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

net/bluetooth/l2cap.c

@@ -77,6 +77,8 @@ static void l2cap_sock_kill(struct sock *sk);
 static struct sk_buff *l2cap_build_cmd(struct l2cap_conn *conn,
 				u8 code, u8 ident, u16 dlen, void *data);
 
+static int l2cap_ertm_data_rcv(struct sock *sk, struct sk_buff *skb);
+
 /* ---- L2CAP timers ---- */
 static void l2cap_sock_timeout(unsigned long arg)
 {
@@ -2447,6 +2449,8 @@ static inline void l2cap_ertm_init(struct sock *sk)
 	__skb_queue_head_init(BUSY_QUEUE(sk));
 
 	INIT_WORK(&l2cap_pi(sk)->busy_work, l2cap_busy_work);
+
+	sk->sk_backlog_rcv = l2cap_ertm_data_rcv;
 }
 
 static inline __u8 l2cap_select_mode(__u8 mode, __u16 remote_feat_mask)
@@ -4171,13 +4175,83 @@ static inline int l2cap_data_channel_sframe(struct sock *sk, u16 rx_control, str
 	return 0;
 }
 
+static int l2cap_ertm_data_rcv(struct sock *sk, struct sk_buff *skb)
+{
+	struct l2cap_pinfo *pi = l2cap_pi(sk);
+	u16 control;
+	u8 req_seq;
+	int len, next_tx_seq_offset, req_seq_offset;
+
+	control = get_unaligned_le16(skb->data);
+	skb_pull(skb, 2);
+	len = skb->len;
+
+	/*
+	 * We can just drop the corrupted I-frame here.
+	 * Receiver will miss it and start proper recovery
+	 * procedures and ask retransmission.
+	 */
+	if (l2cap_check_fcs(pi, skb))
+		goto drop;
+
+	if (__is_sar_start(control) && __is_iframe(control))
+		len -= 2;
+
+	if (pi->fcs == L2CAP_FCS_CRC16)
+		len -= 2;
+
+	if (len > pi->mps) {
+		l2cap_send_disconn_req(pi->conn, sk, ECONNRESET);
+		goto drop;
+	}
+
+	req_seq = __get_reqseq(control);
+	req_seq_offset = (req_seq - pi->expected_ack_seq) % 64;
+	if (req_seq_offset < 0)
+		req_seq_offset += 64;
+
+	next_tx_seq_offset =
+		(pi->next_tx_seq - pi->expected_ack_seq) % 64;
+	if (next_tx_seq_offset < 0)
+		next_tx_seq_offset += 64;
+
+	/* check for invalid req-seq */
+	if (req_seq_offset > next_tx_seq_offset) {
+		l2cap_send_disconn_req(pi->conn, sk, ECONNRESET);
+		goto drop;
+	}
+
+	if (__is_iframe(control)) {
+		if (len < 0) {
+			l2cap_send_disconn_req(pi->conn, sk, ECONNRESET);
+			goto drop;
+		}
+
+		l2cap_data_channel_iframe(sk, control, skb);
+	} else {
+		if (len != 0) {
+			BT_ERR("%d", len);
+			l2cap_send_disconn_req(pi->conn, sk, ECONNRESET);
+			goto drop;
+		}
+
+		l2cap_data_channel_sframe(sk, control, skb);
+	}
+
+	return 0;
+
+drop:
+	kfree_skb(skb);
+	return 0;
+}
+
 static inline int l2cap_data_channel(struct l2cap_conn *conn, u16 cid, struct sk_buff *skb)
 {
 	struct sock *sk;
 	struct l2cap_pinfo *pi;
 	u16 control;
-	u8 tx_seq, req_seq;
-	int len, next_tx_seq_offset, req_seq_offset;
+	u8 tx_seq;
+	int len;
 
 	sk = l2cap_get_chan_by_scid(&conn->chan_list, cid);
 	if (!sk) {
@@ -4207,59 +4281,11 @@ static inline int l2cap_data_channel(struct l2cap_conn *conn, u16 cid, struct sk
 		break;
 
 	case L2CAP_MODE_ERTM:
-		control = get_unaligned_le16(skb->data);
-		skb_pull(skb, 2);
-		len = skb->len;
-
-		/*
-		 * We can just drop the corrupted I-frame here.
-		 * Receiver will miss it and start proper recovery
-		 * procedures and ask retransmission.
-		 */
-		if (l2cap_check_fcs(pi, skb))
-			goto drop;
-
-		if (__is_sar_start(control) && __is_iframe(control))
-			len -= 2;
-
-		if (pi->fcs == L2CAP_FCS_CRC16)
-			len -= 2;
-
-		if (len > pi->mps) {
-			l2cap_send_disconn_req(pi->conn, sk, ECONNRESET);
-			goto drop;
-		}
-
-		req_seq = __get_reqseq(control);
-		req_seq_offset = (req_seq - pi->expected_ack_seq) % 64;
-		if (req_seq_offset < 0)
-			req_seq_offset += 64;
-
-		next_tx_seq_offset =
-			(pi->next_tx_seq - pi->expected_ack_seq) % 64;
-		if (next_tx_seq_offset < 0)
-			next_tx_seq_offset += 64;
-
-		/* check for invalid req-seq */
-		if (req_seq_offset > next_tx_seq_offset) {
-			l2cap_send_disconn_req(pi->conn, sk, ECONNRESET);
-			goto drop;
-		}
-
-		if (__is_iframe(control)) {
-			if (len < 0) {
-				l2cap_send_disconn_req(pi->conn, sk, ECONNRESET);
-				goto drop;
-			}
-
-			l2cap_data_channel_iframe(sk, control, skb);
+		if (!sock_owned_by_user(sk)) {
+			l2cap_ertm_data_rcv(sk, skb);
 		} else {
-			if (len != 0) {
-				l2cap_send_disconn_req(pi->conn, sk, ECONNRESET);
+			if (sk_add_backlog(sk, skb))
 				goto drop;
-			}
-
-			l2cap_data_channel_sframe(sk, control, skb);
 		}
 
 		goto done;