mirror of https://github.com/tailscale/tailscale/
net/tstun: add start of Linux TAP support, with DHCP+ARP server
Still very much a prototype (hard-coded IPs, etc) but should be non-invasive enough to submit at this point and iterate from here. Updates #2589 Co-Author: David Crawshaw <crawshaw@tailscale.com> Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>bradfitz/portmap_test
Brad Fitzpatrick
3 years ago
committed by
Brad Fitzpatrick
parent
fd7b738e5b
commit
a729070252
@ -0,0 +1,359 @@
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// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package tstun
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import (
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"fmt"
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"net"
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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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"github.com/insomniacslk/dhcp/dhcpv4"
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"golang.zx2c4.com/wireguard/tun"
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"inet.af/netaddr"
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"inet.af/netstack/tcpip"
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"inet.af/netstack/tcpip/buffer"
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"inet.af/netstack/tcpip/header"
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"inet.af/netstack/tcpip/network/ipv4"
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"inet.af/netstack/tcpip/transport/udp"
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"tailscale.com/net/packet"
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"tailscale.com/types/ipproto"
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)
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// TODO: this was randomly generated once. Maybe do it per process start? But
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// then an upgraded tailscaled would be visible to devices behind it. So
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// maybe instead make it a function of the tailscaled's wireguard public key?
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// For now just hard code it.
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var ourMAC = net.HardwareAddr{0x30, 0x2D, 0x66, 0xEC, 0x7A, 0x93}
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func init() { createTAP = createTAPLinux }
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func createTAPLinux(tapName, bridgeName string) (dev tun.Device, err error) {
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fd, err := syscall.Open("/dev/net/tun", syscall.O_RDWR, 0)
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if err != nil {
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return nil, err
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}
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var ifr struct {
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name [16]byte
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flags uint16
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_ [22]byte
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}
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copy(ifr.name[:], tapName)
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ifr.flags = syscall.IFF_TAP | syscall.IFF_NO_PI
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_, _, errno := syscall.Syscall(syscall.SYS_IOCTL, uintptr(fd), syscall.TUNSETIFF, uintptr(unsafe.Pointer(&ifr)))
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if errno != 0 {
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syscall.Close(fd)
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return nil, errno
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}
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if err = syscall.SetNonblock(fd, true); err != nil {
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syscall.Close(fd)
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return nil, err
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}
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if err := run("ip", "link", "set", "dev", tapName, "up"); err != nil {
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return nil, err
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}
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if bridgeName != "" {
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if err := run("brctl", "addif", bridgeName, tapName); err != nil {
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return nil, err
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}
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}
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dev, _, err = tun.CreateUnmonitoredTUNFromFD(fd) // TODO: MTU
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if err != nil {
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syscall.Close(fd)
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return nil, err
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}
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return dev, nil
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}
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type etherType [2]byte
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var (
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etherTypeARP = etherType{0x08, 0x06}
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etherTypeIPv4 = etherType{0x08, 0x00}
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etherTypeIPv6 = etherType{0x86, 0xDD}
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)
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const ipv4HeaderLen = 20
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const (
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consumePacket = true
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passOnPacket = false
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)
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// handleTAPFrame handles receiving a raw TAP ethernet frame and reports whether
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// it's been handled (that is, whether it should NOT be passed to wireguard).
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func (t *Wrapper) handleTAPFrame(ethBuf []byte) bool {
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if len(ethBuf) < ethernetFrameSize {
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// Corrupt. Ignore.
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if tapDebug {
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t.logf("tap: short TAP frame")
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}
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return consumePacket
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}
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ethDstMAC, ethSrcMAC := ethBuf[:6], ethBuf[6:12]
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_ = ethDstMAC
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et := etherType{ethBuf[12], ethBuf[13]}
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switch et {
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default:
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if tapDebug {
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t.logf("tap: ignoring etherType %v", et)
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}
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return consumePacket // filter out packet we should ignore
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case etherTypeIPv6:
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// TODO: support DHCPv6/ND/etc later. For now pass all to WireGuard.
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if tapDebug {
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t.logf("tap: ignoring IPv6 %v", et)
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}
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return passOnPacket
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case etherTypeIPv4:
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if len(ethBuf) < ethernetFrameSize+ipv4HeaderLen {
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// Bogus IPv4. Eat.
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if tapDebug {
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t.logf("tap: short ipv4")
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}
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return consumePacket
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}
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return t.handleDHCPRequest(ethBuf)
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case etherTypeARP:
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arpPacket := header.ARP(ethBuf[ethernetFrameSize:])
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if !arpPacket.IsValid() {
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// Bogus ARP. Eat.
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return consumePacket
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}
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switch arpPacket.Op() {
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case header.ARPRequest:
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req := arpPacket // better name at this point
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buf := make([]byte, header.EthernetMinimumSize+header.ARPSize)
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// Our ARP "Table" of one:
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var srcMAC [6]byte
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copy(srcMAC[:], ethSrcMAC)
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if old := t.destMAC(); old != srcMAC {
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t.destMACAtomic.Store(srcMAC)
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}
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eth := header.Ethernet(buf)
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eth.Encode(&header.EthernetFields{
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SrcAddr: tcpip.LinkAddress(ourMAC[:]),
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DstAddr: tcpip.LinkAddress(ethSrcMAC),
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Type: 0x0806, // arp
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})
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res := header.ARP(buf[header.EthernetMinimumSize:])
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res.SetIPv4OverEthernet()
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res.SetOp(header.ARPReply)
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// If the client's asking about their own IP, tell them it's
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// their own MAC. TODO(bradfitz): remove String allocs.
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if net.IP(req.ProtocolAddressTarget()).String() == theClientIP {
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copy(res.HardwareAddressSender(), ethSrcMAC)
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} else {
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copy(res.HardwareAddressSender(), ourMAC[:])
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}
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copy(res.ProtocolAddressSender(), req.ProtocolAddressTarget())
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copy(res.HardwareAddressTarget(), req.HardwareAddressSender())
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copy(res.ProtocolAddressTarget(), req.ProtocolAddressSender())
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n, err := t.tdev.Write(buf, 0)
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if tapDebug {
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t.logf("tap: wrote ARP reply %v, %v", n, err)
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}
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}
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return consumePacket
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}
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}
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// TODO(bradfitz): remove these hard-coded values and move from a /24 to a /10 CGNAT as the range.
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const theClientIP = "100.70.145.3" // TODO: make dynamic from netmap
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const routerIP = "100.70.145.1" // must be in same netmask (currently hack at /24) as theClientIP
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// handleDHCPRequest handles receiving a raw TAP ethernet frame and reports whether
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// it's been handled as a DHCP request. That is, it reports whether the frame should
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// be ignored by the caller and not passed on.
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func (t *Wrapper) handleDHCPRequest(ethBuf []byte) bool {
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const udpHeader = 8
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if len(ethBuf) < ethernetFrameSize+ipv4HeaderLen+udpHeader {
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if tapDebug {
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t.logf("tap: DHCP short")
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}
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return passOnPacket
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}
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ethDstMAC, ethSrcMAC := ethBuf[:6], ethBuf[6:12]
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if string(ethDstMAC) != "\xff\xff\xff\xff\xff\xff" {
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// Not a broadcast
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if tapDebug {
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t.logf("tap: dhcp no broadcast")
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}
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return passOnPacket
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}
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p := parsedPacketPool.Get().(*packet.Parsed)
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defer parsedPacketPool.Put(p)
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p.Decode(ethBuf[ethernetFrameSize:])
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if p.IPProto != ipproto.UDP || p.Src.Port() != 68 || p.Dst.Port() != 67 {
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// Not a DHCP request.
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if tapDebug {
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t.logf("tap: DHCP wrong meta")
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}
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return passOnPacket
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}
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dp, err := dhcpv4.FromBytes(ethBuf[ethernetFrameSize+ipv4HeaderLen+udpHeader:])
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if err != nil {
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// Bogus. Trash it.
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if tapDebug {
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t.logf("tap: DHCP FromBytes bad")
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}
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return consumePacket
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}
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if tapDebug {
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t.logf("tap: DHCP request: %+v", dp)
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}
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switch dp.MessageType() {
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case dhcpv4.MessageTypeDiscover:
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offer, err := dhcpv4.New(
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dhcpv4.WithReply(dp),
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dhcpv4.WithMessageType(dhcpv4.MessageTypeOffer),
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dhcpv4.WithRouter(net.ParseIP(routerIP)), // the default route
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dhcpv4.WithDNS(net.ParseIP("100.100.100.100")),
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dhcpv4.WithServerIP(net.ParseIP("100.100.100.100")), // TODO: what is this?
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dhcpv4.WithOption(dhcpv4.OptServerIdentifier(net.ParseIP("100.100.100.100"))),
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dhcpv4.WithYourIP(net.ParseIP(theClientIP)),
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dhcpv4.WithLeaseTime(3600), // hour works
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//dhcpv4.WithHwAddr(ethSrcMAC),
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dhcpv4.WithNetmask(net.IPMask(net.ParseIP("255.255.255.0").To4())), // TODO: wrong
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//dhcpv4.WithTransactionID(dp.TransactionID),
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)
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if err != nil {
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t.logf("error building DHCP offer: %v", err)
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return consumePacket
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}
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// Make a layer 2 packet to write out:
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pkt := packLayer2UDP(
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offer.ToBytes(),
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ourMAC, ethSrcMAC,
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netaddr.IPPortFrom(netaddr.IPv4(100, 100, 100, 100), 67), // src
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netaddr.IPPortFrom(netaddr.IPv4(255, 255, 255, 255), 68), // dst
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)
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n, err := t.tdev.Write(pkt, 0)
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if tapDebug {
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t.logf("tap: wrote DHCP OFFER %v, %v", n, err)
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}
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case dhcpv4.MessageTypeRequest:
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ack, err := dhcpv4.New(
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dhcpv4.WithReply(dp),
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dhcpv4.WithMessageType(dhcpv4.MessageTypeAck),
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dhcpv4.WithDNS(net.ParseIP("100.100.100.100")),
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dhcpv4.WithRouter(net.ParseIP(routerIP)), // the default route
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dhcpv4.WithServerIP(net.ParseIP("100.100.100.100")), // TODO: what is this?
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dhcpv4.WithOption(dhcpv4.OptServerIdentifier(net.ParseIP("100.100.100.100"))),
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dhcpv4.WithYourIP(net.ParseIP(theClientIP)), // Hello world
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dhcpv4.WithLeaseTime(3600), // hour works
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dhcpv4.WithNetmask(net.IPMask(net.ParseIP("255.255.255.0").To4())),
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)
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if err != nil {
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t.logf("error building DHCP ack: %v", err)
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return consumePacket
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}
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// Make a layer 2 packet to write out:
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pkt := packLayer2UDP(
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ack.ToBytes(),
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ourMAC, ethSrcMAC,
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netaddr.IPPortFrom(netaddr.IPv4(100, 100, 100, 100), 67), // src
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netaddr.IPPortFrom(netaddr.IPv4(255, 255, 255, 255), 68), // dst
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)
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n, err := t.tdev.Write(pkt, 0)
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if tapDebug {
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t.logf("tap: wrote DHCP ACK %v, %v", n, err)
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}
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default:
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if tapDebug {
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t.logf("tap: unknown DHCP type")
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}
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}
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return consumePacket
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}
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func packLayer2UDP(payload []byte, srcMAC, dstMAC net.HardwareAddr, src, dst netaddr.IPPort) []byte {
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buf := buffer.NewView(header.EthernetMinimumSize + header.UDPMinimumSize + header.IPv4MinimumSize + len(payload))
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payloadStart := len(buf) - len(payload)
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copy(buf[payloadStart:], payload)
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srcB := src.IP().As4()
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srcIP := tcpip.Address(srcB[:])
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dstB := dst.IP().As4()
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dstIP := tcpip.Address(dstB[:])
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// Ethernet header
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eth := header.Ethernet(buf)
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eth.Encode(&header.EthernetFields{
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SrcAddr: tcpip.LinkAddress(srcMAC),
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DstAddr: tcpip.LinkAddress(dstMAC),
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Type: ipv4.ProtocolNumber,
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})
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// IP header
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ipbuf := buf[header.EthernetMinimumSize:]
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ip := header.IPv4(ipbuf)
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ip.Encode(&header.IPv4Fields{
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TotalLength: uint16(len(ipbuf)),
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TTL: 65,
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Protocol: uint8(udp.ProtocolNumber),
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SrcAddr: srcIP,
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DstAddr: dstIP,
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})
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ip.SetChecksum(^ip.CalculateChecksum())
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// UDP header
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u := header.UDP(buf[header.EthernetMinimumSize+header.IPv4MinimumSize:])
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u.Encode(&header.UDPFields{
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SrcPort: src.Port(),
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DstPort: dst.Port(),
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Length: uint16(header.UDPMinimumSize + len(payload)),
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})
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// Calculate the UDP pseudo-header checksum.
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xsum := header.PseudoHeaderChecksum(udp.ProtocolNumber, srcIP, dstIP, uint16(len(u)))
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// Calculate the UDP checksum and set it.
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xsum = header.Checksum(payload, xsum)
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u.SetChecksum(^u.CalculateChecksum(xsum))
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return []byte(buf)
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}
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func run(prog string, args ...string) error {
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cmd := exec.Command(prog, args...)
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cmd.Stdout = os.Stdout
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cmd.Stderr = os.Stderr
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if err := cmd.Run(); err != nil {
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return fmt.Errorf("error running %v: %v", cmd, err)
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}
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return nil
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}
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func (t *Wrapper) destMAC() [6]byte {
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mac, _ := t.destMACAtomic.Load().([6]byte)
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return mac
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}
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func (t *Wrapper) tapWrite(buf []byte, offset int) (int, error) {
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if offset < ethernetFrameSize {
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return 0, fmt.Errorf("[unexpected] weird offset %d for TAP write", offset)
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}
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eth := buf[offset-ethernetFrameSize:]
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dst := t.destMAC()
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copy(eth[:6], dst[:])
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copy(eth[6:12], ourMAC[:])
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et := etherTypeIPv4
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if buf[offset]>>4 == 6 {
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et = etherTypeIPv6
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}
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eth[12], eth[13] = et[0], et[1]
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if tapDebug {
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t.logf("tap: tapWrite off=%v % x", offset, buf)
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}
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return t.tdev.Write(buf, offset-ethernetFrameSize)
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}
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@ -0,0 +1,10 @@
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// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// +build !linux
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package tstun
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func (*Wrapper) handleTAPFrame([]byte) bool { panic("unreachable") }
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func (*Wrapper) tapWrite([]byte, int) (int, error) { panic("unreachable") }
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