mac802154: add comments for llsec issues

While doing a little test with the llsec implementation I saw these
issues. We should move decryption and encruption somewhere else,
otherwise while capturing with wireshark the mac header shows secuirty
fields but the payload is plaintext.

A complete other issue is what doing with HardMAC drivers where the
payload is always plaintext. I think we need a special handling then in
userspace. We currently doesn't support any HardMAC transceivers, so we
should fix the first issue for SoftMAC transceivers.
Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

net/mac802154/rx.c

@@ -87,6 +87,10 @@ ieee802154_subif_frame(struct ieee802154_sub_if_data *sdata,
 
 	skb->dev = sdata->dev;
 
+	/* TODO this should be moved after netif_receive_skb call, otherwise
+	 * wireshark will show a mac header with security fields and the
+	 * payload is already decrypted.
+	 */
 	rc = mac802154_llsec_decrypt(&sdata->sec, skb);
 	if (rc) {
 		pr_debug("decryption failed: %i\n", rc);

net/mac802154/tx.c

@@ -129,6 +129,10 @@ ieee802154_subif_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	struct ieee802154_sub_if_data *sdata = IEEE802154_DEV_TO_SUB_IF(dev);
 	int rc;
 
+	/* TODO we should move it to wpan_dev_hard_header and dev_hard_header
+	 * functions. The reason is wireshark will show a mac header which is
+	 * with security fields but the payload is not encrypted.
+	 */
 	rc = mac802154_llsec_encrypt(&sdata->sec, skb);
 	if (rc) {
 		netdev_warn(dev, "encryption failed: %i\n", rc);