net: macsec: fix the length used to copy the key for offloading

The key length used when offloading macsec to Ethernet or PHY drivers
was set to MACSEC_KEYID_LEN (16), which is an issue as:
- This was never meant to be the key length.
- The key length can be > 16.

Fix this by using MACSEC_MAX_KEY_LEN to store the key (the max length
accepted in uAPI) and secy->key_len to copy it.

Fixes: 3cf3227a ("net: macsec: hardware offloading infrastructure")
Reported-by: Lior Nahmanson <liorna@nvidia.com>
Signed-off-by: Antoine Tenart <atenart@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/macsec.c

@@ -1819,7 +1819,7 @@ static int macsec_add_rxsa(struct sk_buff *skb, struct genl_info *info)
 		ctx.sa.rx_sa = rx_sa;
 		ctx.secy = secy;
 		memcpy(ctx.sa.key, nla_data(tb_sa[MACSEC_SA_ATTR_KEY]),
-		       MACSEC_KEYID_LEN);
+		       secy->key_len);
 
 		err = macsec_offload(ops->mdo_add_rxsa, &ctx);
 		if (err)
@@ -2061,7 +2061,7 @@ static int macsec_add_txsa(struct sk_buff *skb, struct genl_info *info)
 		ctx.sa.tx_sa = tx_sa;
 		ctx.secy = secy;
 		memcpy(ctx.sa.key, nla_data(tb_sa[MACSEC_SA_ATTR_KEY]),
-		       MACSEC_KEYID_LEN);
+		       secy->key_len);
 
 		err = macsec_offload(ops->mdo_add_txsa, &ctx);
 		if (err)

include/net/macsec.h

@@ -241,7 +241,7 @@ struct macsec_context {
 	struct macsec_rx_sc *rx_sc;
 	struct {
 		unsigned char assoc_num;
-		u8 key[MACSEC_KEYID_LEN];
+		u8 key[MACSEC_MAX_KEY_LEN];
 		union {
 			struct macsec_rx_sa *rx_sa;
 			struct macsec_tx_sa *tx_sa;