Bluetooth: Implement LE L2CAP reassembly

When receiving fragments over an LE Connection oriented Channel they
need to be collected up and eventually merged into a single SDU. This
patch adds the necessary code for collecting up the fragment skbs to the
channel context and passing them to the recv() callback when the entire
SDU has been received.
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

net/bluetooth/l2cap_core.c

@@ -6818,18 +6818,91 @@ static void l2cap_chan_le_send_credits(struct l2cap_chan *chan)
 
 static int l2cap_le_data_rcv(struct l2cap_chan *chan, struct sk_buff *skb)
 {
-	if (!chan->rx_credits)
+	int err;
+
+	if (!chan->rx_credits) {
+		BT_ERR("No credits to receive LE L2CAP data");
 		return -ENOBUFS;
+	}
 
-	if (chan->imtu < skb->len)
+	if (chan->imtu < skb->len) {
+		BT_ERR("Too big LE L2CAP PDU");
 		return -ENOBUFS;
+	}
 
 	chan->rx_credits--;
 	BT_DBG("rx_credits %u -> %u", chan->rx_credits + 1, chan->rx_credits);
 
 	l2cap_chan_le_send_credits(chan);
 
+	err = 0;
+
+	if (!chan->sdu) {
+		u16 sdu_len;
+
+		sdu_len = get_unaligned_le16(skb->data);
+		skb_pull(skb, L2CAP_SDULEN_SIZE);
+
+		BT_DBG("Start of new SDU. sdu_len %u skb->len %u imtu %u",
+		       sdu_len, skb->len, chan->imtu);
+
+		if (sdu_len > chan->imtu) {
+			BT_ERR("Too big LE L2CAP SDU length received");
+			err = -EMSGSIZE;
+			goto failed;
+		}
+
+		if (skb->len > sdu_len) {
+			BT_ERR("Too much LE L2CAP data received");
+			err = -EINVAL;
+			goto failed;
+		}
+
+		if (skb->len == sdu_len)
 			return chan->ops->recv(chan, skb);
+
+		chan->sdu = skb;
+		chan->sdu_len = sdu_len;
+		chan->sdu_last_frag = skb;
+
+		return 0;
+	}
+
+	BT_DBG("SDU fragment. chan->sdu->len %u skb->len %u chan->sdu_len %u",
+	       chan->sdu->len, skb->len, chan->sdu_len);
+
+	if (chan->sdu->len + skb->len > chan->sdu_len) {
+		BT_ERR("Too much LE L2CAP data received");
+		err = -EINVAL;
+		goto failed;
+	}
+
+	append_skb_frag(chan->sdu, skb, &chan->sdu_last_frag);
+	skb = NULL;
+
+	if (chan->sdu->len == chan->sdu_len) {
+		err = chan->ops->recv(chan, chan->sdu);
+		if (!err) {
+			chan->sdu = NULL;
+			chan->sdu_last_frag = NULL;
+			chan->sdu_len = 0;
+		}
+	}
+
+failed:
+	if (err) {
+		kfree_skb(skb);
+		kfree_skb(chan->sdu);
+		chan->sdu = NULL;
+		chan->sdu_last_frag = NULL;
+		chan->sdu_len = 0;
+	}
+
+	/* We can't return an error here since we took care of the skb
+	 * freeing internally. An error return would cause the caller to
+	 * do a double-free of the skb.
+	 */
+	return 0;
 }
 
 static void l2cap_data_channel(struct l2cap_conn *conn, u16 cid,