netkit: Fix setting mac address in l2 mode

When running Cilium connectivity test suite with netkit in L2 mode, we
found that it is expected to be able to specify a custom MAC address for
the devices, in particular, cilium-cni obtains the specified MAC address
by querying the endpoint and sets the MAC address of the interface inside
the Pod. Thus, fix the missing support in netkit for L2 mode.

Fixes: 35dfaad7 ("netkit, bpf: Add bpf programmable net device")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Nikolay Aleksandrov <razor@blackwall.org>
Acked-by: Stanislav Fomichev <sdf@google.com>
Link: https://lore.kernel.org/r/20240524163619.26001-1-daniel@iogearbox.netSigned-off-by: Alexei Starovoitov <ast@kernel.org>

drivers/net/netkit.c

@@ -155,6 +155,16 @@ static void netkit_set_multicast(struct net_device *dev)
 	/* Nothing to do, we receive whatever gets pushed to us! */
 }
 
+static int netkit_set_macaddr(struct net_device *dev, void *sa)
+{
+	struct netkit *nk = netkit_priv(dev);
+
+	if (nk->mode != NETKIT_L2)
+		return -EOPNOTSUPP;
+
+	return eth_mac_addr(dev, sa);
+}
+
 static void netkit_set_headroom(struct net_device *dev, int headroom)
 {
 	struct netkit *nk = netkit_priv(dev), *nk2;
@@ -198,6 +208,7 @@ static const struct net_device_ops netkit_netdev_ops = {
 	.ndo_start_xmit		= netkit_xmit,
 	.ndo_set_rx_mode	= netkit_set_multicast,
 	.ndo_set_rx_headroom	= netkit_set_headroom,
+	.ndo_set_mac_address	= netkit_set_macaddr,
 	.ndo_get_iflink		= netkit_get_iflink,
 	.ndo_get_peer_dev	= netkit_peer_dev,
 	.ndo_get_stats64	= netkit_get_stats,
@@ -300,9 +311,11 @@ static int netkit_validate(struct nlattr *tb[], struct nlattr *data[],
 
 	if (!attr)
 		return 0;
-	NL_SET_ERR_MSG_ATTR(extack, attr,
-			    "Setting Ethernet address is not supported");
-	return -EOPNOTSUPP;
+	if (nla_len(attr) != ETH_ALEN)
+		return -EINVAL;
+	if (!is_valid_ether_addr(nla_data(attr)))
+		return -EADDRNOTAVAIL;
+	return 0;
 }
 
 static struct rtnl_link_ops netkit_link_ops;
@@ -365,6 +378,9 @@ static int netkit_new_link(struct net *src_net, struct net_device *dev,
 		strscpy(ifname, "nk%d", IFNAMSIZ);
 		ifname_assign_type = NET_NAME_ENUM;
 	}
+	if (mode != NETKIT_L2 &&
+	    (tb[IFLA_ADDRESS] || tbp[IFLA_ADDRESS]))
+		return -EOPNOTSUPP;
 
 	net = rtnl_link_get_net(src_net, tbp);
 	if (IS_ERR(net))
@@ -379,7 +395,7 @@ static int netkit_new_link(struct net *src_net, struct net_device *dev,
 
 	netif_inherit_tso_max(peer, dev);
 
-	if (mode == NETKIT_L2)
+	if (mode == NETKIT_L2 && !(ifmp && tbp[IFLA_ADDRESS]))
 		eth_hw_addr_random(peer);
 	if (ifmp && dev->ifindex)
 		peer->ifindex = ifmp->ifi_index;
@@ -402,7 +418,7 @@ static int netkit_new_link(struct net *src_net, struct net_device *dev,
 	if (err < 0)
 		goto err_configure_peer;
 
-	if (mode == NETKIT_L2)
+	if (mode == NETKIT_L2 && !tb[IFLA_ADDRESS])
 		eth_hw_addr_random(dev);
 	if (tb[IFLA_IFNAME])
 		nla_strscpy(dev->name, tb[IFLA_IFNAME], IFNAMSIZ);