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https://github.com/soypat/lneto.git
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soypat
116 lines
2.9 KiB
Go
116 lines
2.9 KiB
Go
//go:build linux && !baremetal
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package internal
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import (
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"errors"
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"fmt"
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"net/netip"
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"os"
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"os/exec"
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"syscall"
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"unsafe"
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)
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type Tap struct {
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fd int // points to /dev/net/tun device.
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name string
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}
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func NewTap(name string, ip netip.Prefix) (*Tap, error) {
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if len(name) >= syscall.IFNAMSIZ {
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return nil, errors.New("name too large")
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}
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fd, err := syscall.Open("/dev/net/tun", os.O_RDWR, 0777)
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if err != nil {
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return nil, fmt.Errorf("failed to open tun device: %w", err)
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}
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tap := Tap{
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name: name,
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fd: fd,
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}
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ifr := tap.ifreq()
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// Set the flags (starting at offset IFNAMSIZ).
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flags := uint16(syscall.IFF_TAP | syscall.IFF_NO_PI)
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ifr.setflags(flags)
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// Issue the ioctl to create the interface.
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err = ioctl(fd, syscall.TUNSETIFF, ifr.ptr())
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if err != nil {
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return nil, fmt.Errorf("creating tap interface: %w", err)
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}
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if ip.IsValid() {
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// Optionally, bring the interface up and assign an IP address.
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// You can do this using the 'ip' command for simplicity.
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err = exec.Command("ip", "link", "set", "dev", name, "up").Run()
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if err != nil {
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return nil, fmt.Errorf("failed to set ip link: %w", err)
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}
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err = exec.Command("ip", "addr", "add", ip.String(), "dev", name).Run()
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if err != nil {
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return nil, fmt.Errorf("failed to assign IP address: %w", err)
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}
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}
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return &Tap{fd: fd, name: name}, nil
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}
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func (tap *Tap) Read(b []byte) (int, error) {
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return syscall.Read(tap.fd, b)
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}
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func (tap *Tap) Write(b []byte) (int, error) {
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return syscall.Write(tap.fd, b)
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}
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func (tap *Tap) Close() error {
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return syscall.Close(tap.fd)
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}
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func ioctl(fd int, request uintptr, argp unsafe.Pointer) error {
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_, _, errno := syscall.Syscall(syscall.SYS_IOCTL, uintptr(fd), request, uintptr(argp))
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if errno != 0 {
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return os.NewSyscallError("ioctl", errno)
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}
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return nil
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}
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func (tap *Tap) HardwareAddress6() (hw [6]byte, err error) {
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// We cannot use tap.sock to query the hardware address, this is something known by the network stack, so get a sock to network stack.
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sock, err := syscall.Socket(syscall.AF_INET, syscall.SOCK_DGRAM, syscall.IPPROTO_IP)
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if err != nil {
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return hw, fmt.Errorf("socket open: %w", err)
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}
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defer syscall.Close(sock)
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ifr := tap.ifreq()
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err = ioctl(sock, syscall.SIOCGIFHWADDR, ifr.ptr())
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if err != nil {
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return hw, err
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}
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sa_family := *(*uint16)(unsafe.Pointer(&ifr.Data[0]))
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if sa_family != 1 {
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return hw, fmt.Errorf("expecting sa_family=1 got %d", sa_family)
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}
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copy(hw[:], ifr.Data[2:]) // first two bytes are sa_family
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return hw, nil
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}
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type ifreq struct {
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Name [syscall.IFNAMSIZ]byte
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Data [64]byte // union data (covers ifr_hwaddr, etc.)
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}
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func (ifr *ifreq) setflags(flags uint16) {
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*(*uint16)(unsafe.Pointer(&ifr.Data[0])) = flags
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}
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func (ifr *ifreq) ptr() unsafe.Pointer { return unsafe.Pointer(ifr) }
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func (tap *Tap) ifreq() ifreq {
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// Set the name; it will be zero-padded automatically.
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var ifr ifreq
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copy(ifr.Name[:], tap.name)
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return ifr
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}
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