dhcp4: use the configured (not the current) MAC address

This fixes a race where dhcp4 started before netconfigd had a chance to change
the hardware address on the uplink0 interface.

fiber7’s port security feature may result in an about hour-long internet outage
without this commit.

cmd/dhcp4/dhcp4.go

@@ -33,6 +33,7 @@ import (
 	"github.com/google/renameio"
 	"github.com/jpillora/backoff"
 	"github.com/rtr7/router7/internal/dhcp4"
+	"github.com/rtr7/router7/internal/netconfig"
 	"github.com/rtr7/router7/internal/notify"
 	"github.com/rtr7/router7/internal/teelogger"
 )
@@ -48,6 +49,20 @@ func logic() error {
 	if err != nil {
 		return err
 	}
+	hwaddr := iface.HardwareAddr
+	// The interface may not have been configured by netconfigd yet and might
+	// still use the old hardware address. We overwrite it with the address that
+	// netconfigd is going to use to fix this issue without additional
+	// synchronization.
+	details, err := netconfig.Interface("/perm", "uplink0")
+	if err != nil {
+		return err
+	}
+	if spoof := details.SpoofHardwareAddr; spoof != "" {
+		if addr, err := net.ParseMAC(spoof); err == nil {
+			hwaddr = addr
+		}
+	}
 	const ackFn = "/perm/dhcp4/wire/ack"
 	var ack *layers.DHCPv4
 	ackB, err := ioutil.ReadFile(ackFn)
@@ -61,6 +76,7 @@ func logic() error {
 	}
 	c := dhcp4.Client{
 		Interface: iface,
+		HWAddr:    hwaddr,
 		Ack:       ack,
 	}
 	usr2 := make(chan os.Signal, 1)

internal/dhcp4/dhcp4.go

@@ -40,6 +40,7 @@ type Config struct {
 
 type Client struct {
 	Interface *net.Interface // e.g. net.InterfaceByName("eth0")
+	HWAddr    net.HardwareAddr
 
 	err          error
 	once         sync.Once
@@ -102,6 +103,9 @@ func (c *Client) ObtainOrRenew() bool {
 			onceErr = fmt.Errorf("Interface is nil")
 			return
 		}
+		if c.hardwareAddr == nil && c.HWAddr != nil {
+			c.hardwareAddr = c.HWAddr
+		}
 		if c.hardwareAddr == nil {
 			c.hardwareAddr = c.Interface.HardwareAddr
 		}

internal/netconfig/netconfig.go

@@ -184,26 +184,36 @@ type InterfaceConfig struct {
 	Interfaces []InterfaceDetails `json:"interfaces"`
 }
 
-// LinkAddress returns the IP address configured for the interface ifname in
+// Interface returns the InterfaceDetails configured for interface ifname in
 // interfaces.json.
-func LinkAddress(dir, ifname string) (net.IP, error) {
+func Interface(dir, ifname string) (InterfaceDetails, error) {
 	fn := filepath.Join(dir, "interfaces.json")
 	b, err := ioutil.ReadFile(fn)
 	if err != nil {
-		return nil, err
+		return InterfaceDetails{}, err
 	}
 	var cfg InterfaceConfig
 	if err := json.Unmarshal(b, &cfg); err != nil {
-		return nil, err
+		return InterfaceDetails{}, err
 	}
 	for _, details := range cfg.Interfaces {
 		if details.Name != ifname {
 			continue
 		}
-		ip, _, err := net.ParseCIDR(details.Addr)
+		return details, nil
-		return ip, err
 	}
-	return nil, fmt.Errorf("%s does not configure interface %q", fn, ifname)
+	return InterfaceDetails{}, fmt.Errorf("%s does not configure interface %q", fn, ifname)
+}
+
+// LinkAddress returns the IP address configured for the interface ifname in
+// interfaces.json.
+func LinkAddress(dir, ifname string) (net.IP, error) {
+	iface, err := Interface(dir, ifname)
+	if err != nil {
+		return nil, err
+	}
+	ip, _, err := net.ParseCIDR(iface.Addr)
+	return ip, err
 }
 
 func applyInterfaces(dir, root string) error {