net/tstun: block looped disco traffic

Updates #1526 (maybe fixes? time will tell)

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This commit is contained in:
Brad Fitzpatrick 2021-09-13 14:21:40 -07:00 committed by Brad Fitzpatrick
parent 3759fb8987
commit dabeda21e0
4 changed files with 82 additions and 0 deletions

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@ -57,6 +57,16 @@ func LooksLikeDiscoWrapper(p []byte) bool {
return string(p[:len(Magic)]) == Magic
}
// Source returns the slice of p that represents the
// disco public key source, and whether p looks like
// a disco message.
func Source(p []byte) (src []byte, ok bool) {
if !LooksLikeDiscoWrapper(p) {
return nil, false
}
return p[len(Magic):][:keyLen], true
}
// Parse parses the encrypted part of the message from inside the
// nacl secretbox.
func Parse(p []byte) (Message, error) {

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@ -7,6 +7,7 @@
package tstun
import (
"bytes"
"errors"
"fmt"
"io"
@ -19,7 +20,9 @@ import (
"golang.zx2c4.com/wireguard/device"
"golang.zx2c4.com/wireguard/tun"
"inet.af/netaddr"
"tailscale.com/disco"
"tailscale.com/net/packet"
"tailscale.com/tailcfg"
"tailscale.com/tstime/mono"
"tailscale.com/types/ipproto"
"tailscale.com/types/logger"
@ -76,6 +79,7 @@ type Wrapper struct {
destIPActivity atomic.Value // of map[netaddr.IP]func()
destMACAtomic atomic.Value // of [6]byte
discoKey atomic.Value // of tailcfg.DiscoKey
// buffer stores the oldest unconsumed packet from tdev.
// It is made a static buffer in order to avoid allocations.
@ -196,6 +200,30 @@ func (t *Wrapper) SetDestIPActivityFuncs(m map[netaddr.IP]func()) {
t.destIPActivity.Store(m)
}
// SetDiscoKey sets the current discovery key.
//
// It is only used for filtering out bogus traffic when network
// stack(s) get confused; see Issue 1526.
func (t *Wrapper) SetDiscoKey(k tailcfg.DiscoKey) {
t.discoKey.Store(k)
}
// isSelfDisco reports whether packet p
// looks like a Disco packet from ourselves.
// See Issue 1526.
func (t *Wrapper) isSelfDisco(p *packet.Parsed) bool {
if p.IPProto != ipproto.UDP {
return false
}
pkt := p.Payload()
discoSrc, ok := disco.Source(pkt)
if !ok {
return false
}
selfDiscoPub, ok := t.discoKey.Load().(tailcfg.DiscoKey)
return ok && bytes.Equal(selfDiscoPub[:], discoSrc)
}
func (t *Wrapper) Close() error {
var err error
t.closeOnce.Do(func() {
@ -483,6 +511,16 @@ func (t *Wrapper) filterIn(buf []byte) filter.Response {
}
}
// Issue 1526 workaround: if we see disco packets over
// Tailscale from ourselves, then drop them, as that shouldn't
// happen unless a networking stack is confused, as it seems
// macOS in Network Extension mode might be.
if p.IPProto == ipproto.UDP && // disco is over UDP; avoid isSelfDisco call for TCP/etc
t.isSelfDisco(p) {
t.logf("[unexpected] received self disco package over tstun; dropping")
return filter.DropSilently
}
if t.PreFilterIn != nil {
if res := t.PreFilterIn(p, t); res.IsDrop() {
return res

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@ -15,7 +15,10 @@ import (
"golang.zx2c4.com/wireguard/tun/tuntest"
"inet.af/netaddr"
"tailscale.com/disco"
"tailscale.com/net/packet"
"tailscale.com/tailcfg"
"tailscale.com/tstest"
"tailscale.com/tstime/mono"
"tailscale.com/types/ipproto"
"tailscale.com/types/logger"
@ -486,3 +489,32 @@ func TestPeerAPIBypass(t *testing.T) {
})
}
}
// Issue 1526: drop disco frames from ourselves.
func TestFilterDiscoLoop(t *testing.T) {
var memLog tstest.MemLogger
discoPub := tailcfg.DiscoKey{1: 1, 2: 2}
tw := &Wrapper{logf: memLog.Logf}
tw.SetDiscoKey(discoPub)
uh := packet.UDP4Header{
IP4Header: packet.IP4Header{
IPProto: ipproto.UDP,
Src: netaddr.IPv4(1, 2, 3, 4),
Dst: netaddr.IPv4(5, 6, 7, 8),
},
SrcPort: 9,
DstPort: 10,
}
discoPayload := fmt.Sprintf("%s%s%s", disco.Magic, discoPub[:], [disco.NonceLen]byte{})
pkt := make([]byte, uh.Len()+len(discoPayload))
uh.Marshal(pkt)
copy(pkt[uh.Len():], discoPayload)
got := tw.filterIn(pkt)
if got != filter.DropSilently {
t.Errorf("got %v; want DropSilently", got)
}
if got, want := memLog.String(), "[unexpected] received self disco package over tstun; dropping\n"; got != want {
t.Errorf("log output mismatch\n got: %q\nwant: %q\n", got, want)
}
}

View File

@ -332,6 +332,8 @@ func NewUserspaceEngine(logf logger.Logf, conf Config) (_ Engine, reterr error)
closePool.add(e.magicConn)
e.magicConn.SetNetworkUp(e.linkMon.InterfaceState().AnyInterfaceUp())
tsTUNDev.SetDiscoKey(e.magicConn.DiscoPublicKey())
if conf.RespondToPing {
e.tundev.PostFilterIn = echoRespondToAll
}