net/mlx5e/core/en_fs: fix pointer dereference after free in mlx5e_execute_l2_action

hn is being kfree'd in mlx5e_del_l2_from_hash and then dereferenced
by accessing hn->ai.addr

Fix this by copying the MAC address into a local variable for its safe use
in all possible execution paths within function mlx5e_execute_l2_action.

Addresses-Coverity-ID: 1417789
Fixes: eeb66cdb6826 ("net/mlx5: Separate between E-Switch and MPFS")
Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com>
Acked-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlx5/core/en_fs.c

@@ -365,21 +365,24 @@ static void mlx5e_execute_l2_action(struct mlx5e_priv *priv,
 				    struct mlx5e_l2_hash_node *hn)
 {
 	u8 action = hn->action;
+	u8 mac_addr[ETH_ALEN];
 	int l2_err = 0;
 
+	ether_addr_copy(mac_addr, hn->ai.addr);
+
 	switch (action) {
 	case MLX5E_ACTION_ADD:
 		mlx5e_add_l2_flow_rule(priv, &hn->ai, MLX5E_FULLMATCH);
-		if (!is_multicast_ether_addr(hn->ai.addr)) {
-			l2_err = mlx5_mpfs_add_mac(priv->mdev, hn->ai.addr);
+		if (!is_multicast_ether_addr(mac_addr)) {
+			l2_err = mlx5_mpfs_add_mac(priv->mdev, mac_addr);
 			hn->mpfs = !l2_err;
 		}
 		hn->action = MLX5E_ACTION_NONE;
 		break;
 
 	case MLX5E_ACTION_DEL:
-		if (!is_multicast_ether_addr(hn->ai.addr) && hn->mpfs)
-			l2_err = mlx5_mpfs_del_mac(priv->mdev, hn->ai.addr);
+		if (!is_multicast_ether_addr(mac_addr) && hn->mpfs)
+			l2_err = mlx5_mpfs_del_mac(priv->mdev, mac_addr);
 		mlx5e_del_l2_flow_rule(priv, &hn->ai);
 		mlx5e_del_l2_from_hash(hn);
 		break;
@@ -387,7 +390,7 @@ static void mlx5e_execute_l2_action(struct mlx5e_priv *priv,
 
 	if (l2_err)
 		netdev_warn(priv->netdev, "MPFS, failed to %s mac %pM, err(%d)\n",
-			    action == MLX5E_ACTION_ADD ? "add" : "del", hn->ai.addr, l2_err);
+			    action == MLX5E_ACTION_ADD ? "add" : "del", mac_addr, l2_err);
 }
 
 static void mlx5e_sync_netdev_addr(struct mlx5e_priv *priv)