dhcp4: clone HardwareAddr bytes defensively

I suspect that Go’s net package reuses its buffers and these bytes don’t remain
valid forever (perhaps only if the network interfaces of the machine change?).

At least that would explain why my DHCP client sent requests with a wrong address.

Author: stapelberg

internal/dhcp4/dhcp4.go

@@ -20,6 +20,7 @@ import (
 	"errors"
 	"fmt"
 	"net"
+	"slices"
 	"sync"
 	"syscall"
 	"time"
@@ -105,7 +106,9 @@ func (c *Client) ObtainOrRenew() bool {
 			c.hardwareAddr = c.HWAddr
 		}
 		if c.hardwareAddr == nil {
-			c.hardwareAddr = c.Interface.HardwareAddr
+			// Defensive slices.Clone because I noticed c.hardwareAddr
+			// containing an unexpected MAC address (~/2025-08-15-*dhcp4-loss).
+			c.hardwareAddr = slices.Clone(c.Interface.HardwareAddr)
 		}
 		if c.generateXID == nil {
 			c.generateXID = dhcp4.XIDGenerator(c.hardwareAddr)