tun: split tun_{bsd -> freebsd,openbsd}.go

The address ioctl code is just plain broken.

I fixed it for OpenBSD, but have no resources or time for FreeBSD,
so there the code will stay as-is.

FreeBSD also supports stuff like netlink, so perhaps a future rewrite
will look different from OpenBSD's ioctl code (the only approach) anyway.

src/tun/tun_freebsd.go

@@ -1,5 +1,5 @@
-//go:build openbsd || freebsd
+//go:build freebsd
-// +build openbsd freebsd
+// +build freebsd
 
 package tun
 

src/tun/tun_openbsd.go

@@ -0,0 +1,140 @@
+//go:build openbsd
+// +build openbsd
+
+package tun
+
+import (
+	"encoding/binary"
+	"fmt"
+	"os/exec"
+	"strconv"
+	"strings"
+	"syscall"
+	"unsafe"
+
+	"golang.org/x/sys/unix"
+
+	wgtun "golang.zx2c4.com/wireguard/tun"
+)
+
+const SIOCSIFADDR_IN6 = (0x80000000) | ((288 & 0x1fff) << 16) | uint32(byte('i'))<<8 | 12
+
+type in6_addrlifetime struct {
+	ia6t_expire    float64
+	ia6t_preferred float64
+	ia6t_vltime    uint32
+	ia6t_pltime    uint32
+}
+
+type sockaddr_in6 struct {
+	sin6_len      uint8
+	sin6_family   uint8
+	sin6_port     uint8
+	sin6_flowinfo uint32
+	sin6_addr     [8]uint16
+	sin6_scope_id uint32
+}
+
+/*
+from <netinet6/in6_var.h>
+struct  in6_ifreq {
+ 277         char    ifr_name[IFNAMSIZ];
+ 278         union {
+ 279                 struct  sockaddr_in6 ifru_addr;
+ 280                 struct  sockaddr_in6 ifru_dstaddr;
+ 281                 int     ifru_flags;
+ 282                 int     ifru_flags6;
+ 283                 int     ifru_metric;
+ 284                 caddr_t ifru_data;
+ 285                 struct in6_addrlifetime ifru_lifetime;
+ 286                 struct in6_ifstat ifru_stat;
+ 287                 struct icmp6_ifstat ifru_icmp6stat;
+ 288                 u_int32_t ifru_scope_id[16];
+ 289         } ifr_ifru;
+ 290 };
+*/
+
+type in6_ifreq_addr struct {
+	ifr_name  [syscall.IFNAMSIZ]byte
+	ifru_addr sockaddr_in6
+}
+
+type in6_ifreq_flags struct {
+	ifr_name [syscall.IFNAMSIZ]byte
+	flags    int
+}
+
+type in6_ifreq_lifetime struct {
+	ifr_name          [syscall.IFNAMSIZ]byte
+	ifru_addrlifetime in6_addrlifetime
+}
+
+// Configures the TUN adapter with the correct IPv6 address and MTU.
+func (tun *TunAdapter) setup(ifname string, addr string, mtu uint64) error {
+	iface, err := wgtun.CreateTUN(ifname, int(mtu))
+	if err != nil {
+		return fmt.Errorf("failed to create TUN: %w", err)
+	}
+	tun.iface = iface
+	if mtu, err := iface.MTU(); err == nil {
+		tun.mtu = getSupportedMTU(uint64(mtu))
+	} else {
+		tun.mtu = 0
+	}
+	if addr != "" {
+		return tun.setupAddress(addr)
+	}
+	return nil
+}
+
+// Configures the "utun" adapter from an existing file descriptor.
+func (tun *TunAdapter) setupFD(fd int32, addr string, mtu uint64) error {
+	return fmt.Errorf("setup via FD not supported on this platform")
+}
+
+func (tun *TunAdapter) setupAddress(addr string) error {
+	var sfd int
+	var err error
+
+	// Create system socket
+	if sfd, err = unix.Socket(unix.AF_INET, unix.SOCK_DGRAM, 0); err != nil {
+		tun.log.Printf("Create AF_INET socket failed: %v.", err)
+		return err
+	}
+
+	// Friendly output
+	tun.log.Infof("Interface name: %s", tun.Name())
+	tun.log.Infof("Interface IPv6: %s", addr)
+	tun.log.Infof("Interface MTU: %d", tun.mtu)
+
+	// Create the address request
+	// FIXME: I don't work!
+	var ar in6_ifreq_addr
+	copy(ar.ifr_name[:], tun.Name())
+	ar.ifru_addr.sin6_len = uint8(unsafe.Sizeof(ar.ifru_addr))
+	ar.ifru_addr.sin6_family = unix.AF_INET6
+	parts := strings.Split(strings.Split(addr, "/")[0], ":")
+	for i := 0; i < 8; i++ {
+		addr, _ := strconv.ParseUint(parts[i], 16, 16)
+		b := make([]byte, 16)
+		binary.LittleEndian.PutUint16(b, uint16(addr))
+		ar.ifru_addr.sin6_addr[i] = uint16(binary.BigEndian.Uint16(b))
+	}
+
+	// Set the interface address
+	if _, _, errno := unix.Syscall(unix.SYS_IOCTL, uintptr(sfd), uintptr(SIOCSIFADDR_IN6), uintptr(unsafe.Pointer(&ar))); errno != 0 {
+		err = errno
+		tun.log.Errorf("Error in SIOCSIFADDR_IN6: %v", errno)
+
+		// Fall back to ifconfig to set the address
+		cmd := exec.Command("ifconfig", tun.Name(), "inet6", addr)
+		tun.log.Warnf("Using ifconfig as fallback: %v", strings.Join(cmd.Args, " "))
+		output, err := cmd.CombinedOutput()
+		if err != nil {
+			tun.log.Errorf("SIOCSIFADDR_IN6 fallback failed: %v.", err)
+			tun.log.Traceln(string(output))
+		}
+	}
+
+	return nil
+}