143 lines
3.7 KiB
Go
143 lines
3.7 KiB
Go
package stage3
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import (
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"fmt"
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"io"
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"net"
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"os"
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"syscall"
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"golang.org/x/sys/unix"
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)
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const (
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if_mtu = 1200
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if_queue_len = 1000
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)
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func openInterface(network []byte, localIP byte, name string) (io.ReadWriteCloser, error) {
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if len(network) != 4 {
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return nil, fmt.Errorf("expected network to be 4 bytes, got %d", len(network))
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}
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ip := net.IPv4(network[0], network[1], network[2], localIP)
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//////////////////////////
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// Create TUN Interface //
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//////////////////////////
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tunFD, err := syscall.Open("/dev/net/tun", syscall.O_RDWR|unix.O_CLOEXEC, 0600)
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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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// New interface request.
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req, err := unix.NewIfreq(name)
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if err != nil {
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return nil, fmt.Errorf("failed to create new TUN interface request: %w", err)
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}
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// Flags:
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//
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// IFF_NO_PI => don't add packet info data to packets sent to the interface.
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// IFF_TUN => create a TUN device handling IP packets.
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req.SetUint16(unix.IFF_NO_PI | unix.IFF_TUN)
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err = unix.IoctlIfreq(tunFD, unix.TUNSETIFF, req)
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if err != nil {
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return nil, fmt.Errorf("failed to set TUN device settings: %w", err)
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}
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// Name may not be exactly the same?
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name = req.Name()
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/////////////
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// Set MTU //
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/////////////
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// We need a socket file descriptor to set other options for some reason.
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sockFD, err := unix.Socket(unix.AF_INET, unix.SOCK_DGRAM, unix.IPPROTO_IP)
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if err != nil {
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return nil, fmt.Errorf("failed to open socket: %w", err)
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}
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defer unix.Close(sockFD)
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req, err = unix.NewIfreq(name)
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if err != nil {
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return nil, fmt.Errorf("failed to create MTU interface request: %w", err)
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}
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req.SetUint32(if_mtu)
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if err = unix.IoctlIfreq(sockFD, unix.SIOCSIFMTU, req); err != nil {
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return nil, fmt.Errorf("failed to set interface MTU: %w", err)
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}
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//////////////////////
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// Set Queue Length //
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//////////////////////
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req, err = unix.NewIfreq(name)
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if err != nil {
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return nil, fmt.Errorf("failed to create IP interface request: %w", err)
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}
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req.SetUint16(if_queue_len)
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if err = unix.IoctlIfreq(sockFD, unix.SIOCSIFTXQLEN, req); err != nil {
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return nil, fmt.Errorf("failed to set interface queue length: %w", err)
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}
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/////////////////////
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// Set IP and Mask //
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/////////////////////
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req, err = unix.NewIfreq(name)
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if err != nil {
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return nil, fmt.Errorf("failed to create IP interface request: %w", err)
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}
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if err := req.SetInet4Addr(ip.To4()); err != nil {
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return nil, fmt.Errorf("failed to set interface request IP: %w", err)
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}
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if err = unix.IoctlIfreq(sockFD, unix.SIOCSIFADDR, req); err != nil {
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return nil, fmt.Errorf("failed to set interface IP: %w", err)
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}
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// SET MASK - must happen after setting address.
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req, err = unix.NewIfreq(name)
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if err != nil {
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return nil, fmt.Errorf("failed to create mask interface request: %w", err)
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}
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if err := req.SetInet4Addr(net.IPv4(255, 255, 255, 0).To4()); err != nil {
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return nil, fmt.Errorf("failed to set interface request mask: %w", err)
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}
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if err := unix.IoctlIfreq(sockFD, unix.SIOCSIFNETMASK, req); err != nil {
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return nil, fmt.Errorf("failed to set interface mask: %w", err)
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}
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////////////////////////
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// Bring Interface Up //
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////////////////////////
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req, err = unix.NewIfreq(name)
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if err != nil {
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return nil, fmt.Errorf("failed to create up interface request: %w", err)
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}
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// Get current flags.
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if err = unix.IoctlIfreq(sockFD, unix.SIOCGIFFLAGS, req); err != nil {
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return nil, fmt.Errorf("failed to get interface flags: %w", err)
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}
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flags := req.Uint16() | unix.IFF_UP | unix.IFF_RUNNING
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// Set UP flag / broadcast flags.
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req.SetUint16(flags)
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if err = unix.IoctlIfreq(sockFD, unix.SIOCSIFFLAGS, req); err != nil {
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return nil, fmt.Errorf("failed to set interface up: %w", err)
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}
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return os.NewFile(uintptr(tunFD), "tun"), nil
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}
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