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tsdns: dual resolution mode, IPv6 support (#526)

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This change adds to tsdns the ability to delegate lookups to upstream nameservers.
This is crucial for setting Magic DNS as the system resolver.

Signed-off-by: Dmytro Shynkevych <dmytro@tailscale.com>
This commit is contained in:
Dmytro Shynkevych
2020-07-07 15:25:32 -04:00
committed by GitHub
parent ce1b52bb71
commit 67ebba90e1
7 changed files with 555 additions and 257 deletions
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64
wgengine/userspace.go
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@@ -25,6 +25,7 @@ import (
"github.com/tailscale/wireguard-go/tun"
"github.com/tailscale/wireguard-go/wgcfg"
"go4.org/mem"
"inet.af/netaddr"
"tailscale.com/control/controlclient"
"tailscale.com/internal/deepprint"
"tailscale.com/ipn/ipnstate"
@@ -51,6 +52,11 @@ import (
// discovery.
const minimalMTU = 1280
const (
magicDNSIP = 0x64646464 // 100.100.100.100
magicDNSPort = 53
)
type userspaceEngine struct {
logf logger.Logf
reqCh chan struct{}
@@ -100,7 +106,7 @@ type EngineConfig struct {
// EchoRespondToAll determines whether ICMP Echo requests incoming from Tailscale peers
// will be intercepted and responded to, regardless of the source host.
EchoRespondToAll bool
// UseTailscaleDNS determines whether DNS requests for names of the form *.ipn.dev
// UseTailscaleDNS determines whether DNS requests for names of the form <mynode>.<mydomain>.<root>
// directed to the designated Taislcale DNS address (see wgengine/tsdns)
// will be intercepted and resolved by a tsdns.Resolver.
UseTailscaleDNS bool
@@ -174,7 +180,7 @@ func newUserspaceEngineAdvanced(conf EngineConfig) (_ Engine, reterr error) {
reqCh: make(chan struct{}, 1),
waitCh: make(chan struct{}),
tundev: tstun.WrapTUN(logf, conf.TUN),
resolver: tsdns.NewResolver(logf),
resolver: tsdns.NewResolver(logf, "tailscale.us"),
useTailscaleDNS: conf.UseTailscaleDNS,
pingers: make(map[wgcfg.Key]*pinger),
}
@@ -308,6 +314,9 @@ func newUserspaceEngineAdvanced(conf EngineConfig) (_ Engine, reterr error) {
e.linkMon.Start()
e.magicConn.Start()
e.resolver.Start()
go e.pollResolver()
return e, nil
}
@@ -360,22 +369,52 @@ func (e *userspaceEngine) isLocalAddr(ip packet.IP) bool {
// handleDNS is an outbound pre-filter resolving Tailscale domains.
func (e *userspaceEngine) handleDNS(p *packet.ParsedPacket, t *tstun.TUN) filter.Response {
if e.resolver.AcceptsPacket(p) {
// TODO(dmytro): avoid this allocation without having tsdns know tstun quirks.
buf := make([]byte, tstun.MaxPacketSize)
offset := tstun.PacketStartOffset
response, err := e.resolver.Respond(p, buf[offset:])
if err != nil {
e.logf("DNS resolver error: %v", err)
} else {
t.InjectInboundDirect(buf[:offset+len(response)], offset)
if p.DstIP == magicDNSIP && p.DstPort == magicDNSPort && p.IPProto == packet.UDP {
request := tsdns.Packet{
Payload: p.Payload(),
Addr: netaddr.IPPort{IP: p.SrcIP.Netaddr(), Port: p.SrcPort},
}
err := e.resolver.EnqueueRequest(request)
if err != nil {
e.logf("tsdns: enqueue: %v", err)
}
// We already handled it, stop.
return filter.Drop
}
return filter.Accept
}
// pollResolver reads responses from the DNS resolver and injects them inbound.
func (e *userspaceEngine) pollResolver() {
for {
resp, err := e.resolver.NextResponse()
if err == tsdns.ErrClosed {
return
}
if err != nil {
e.logf("tsdns: error: %v", err)
continue
}
h := packet.UDPHeader{
IPHeader: packet.IPHeader{
SrcIP: packet.IP(magicDNSIP),
DstIP: packet.IPFromNetaddr(resp.Addr.IP),
},
SrcPort: magicDNSPort,
DstPort: resp.Addr.Port,
}
hlen := h.Len()
// TODO(dmytro): avoid this allocation without importing tstun quirks into tsdns.
const offset = tstun.PacketStartOffset
buf := make([]byte, offset+hlen+len(resp.Payload))
copy(buf[offset+hlen:], resp.Payload)
h.Marshal(buf[offset:])
e.tundev.InjectInboundDirect(buf, offset)
}
}
// pinger sends ping packets for a few seconds.
//
// These generated packets are used to ensure we trigger the spray logic in
@@ -759,6 +798,7 @@ func (e *userspaceEngine) Close() {
r := bufio.NewReader(strings.NewReader(""))
e.wgdev.IpcSetOperation(r)
e.resolver.Close()
e.magicConn.Close()
e.linkMon.Close()
e.router.Close()