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cmd/natc: add --ignore-destinations flag

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Updates tailscale/corp#20503

Signed-off-by: Fran Bull <fran@tailscale.com>
pull/12366/head
Fran Bull 3 weeks ago committed by franbull
parent 9cdb33e2a4
commit d2d459d442
1 changed files with 137 additions and 34 deletions
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171
cmd/natc/natc.go
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@ -48,12 +48,13 @@ func main() {
// Parse flags
fs := flag.NewFlagSet("natc", flag.ExitOnError)
var (
debugPort = fs.Int("debug-port", 8893, "Listening port for debug/metrics endpoint")
hostname = fs.String("hostname", "", "Hostname to register the service under")
siteID = fs.Uint("site-id", 1, "an integer site ID to use for the ULA prefix which allows for multiple proxies to act in a HA configuration")
v4PfxStr = fs.String("v4-pfx", "100.64.1.0/24", "comma-separated list of IPv4 prefixes to advertise")
verboseTSNet = fs.Bool("verbose-tsnet", false, "enable verbose logging in tsnet")
printULA = fs.Bool("print-ula", false, "print the ULA prefix and exit")
debugPort = fs.Int("debug-port", 8893, "Listening port for debug/metrics endpoint")
hostname = fs.String("hostname", "", "Hostname to register the service under")
siteID = fs.Uint("site-id", 1, "an integer site ID to use for the ULA prefix which allows for multiple proxies to act in a HA configuration")
v4PfxStr = fs.String("v4-pfx", "100.64.1.0/24", "comma-separated list of IPv4 prefixes to advertise")
verboseTSNet = fs.Bool("verbose-tsnet", false, "enable verbose logging in tsnet")
printULA = fs.Bool("print-ula", false, "print the ULA prefix and exit")
ignoreDstPfxStr = fs.String("ignore-destinations", "", "comma-separated list of prefixes to ignore")
)
ff.Parse(fs, os.Args[1:], ff.WithEnvVarPrefix("TS_NATC"))
@ -70,6 +71,24 @@ func main() {
log.Fatalf("site-id must be in the range [0, 65535]")
}
var ignoreDstTable *bart.Table[bool]
for _, s := range strings.Split(*ignoreDstPfxStr, ",") {
s := strings.TrimSpace(s)
if s == "" {
continue
}
if ignoreDstTable == nil {
ignoreDstTable = &bart.Table[bool]{}
}
pfx, err := netip.ParsePrefix(s)
if err != nil {
log.Fatalf("unable to parse prefix: %v", err)
}
if pfx.Masked() != pfx {
log.Fatalf("prefix %v is not normalized (bits are set outside the mask)", pfx)
}
ignoreDstTable.Insert(pfx, true)
}
var v4Prefixes []netip.Prefix
for _, s := range strings.Split(*v4PfxStr, ",") {
p := netip.MustParsePrefix(strings.TrimSpace(s))
@ -112,11 +131,12 @@ func main() {
}
c := &connector{
ts: ts,
lc: lc,
dnsAddr: dnsAddr,
v4Ranges: v4Prefixes,
v6ULA: ula(uint16(*siteID)),
ts: ts,
lc: lc,
dnsAddr: dnsAddr,
v4Ranges: v4Prefixes,
v6ULA: ula(uint16(*siteID)),
ignoreDsts: ignoreDstTable,
}
c.run(ctx)
}
@ -139,6 +159,15 @@ type connector struct {
v6ULA netip.Prefix
perPeerMap syncs.Map[tailcfg.NodeID, *perPeerState]
// ignoreDsts is initialized at start up with the contents of --ignore-destinations (if none it is nil)
// It is never mutated, only used for lookups.
// Users who want to natc a DNS wildcard but not every address record in that domain can supply the
// exceptions in --ignore-destinations. When we receive a dns request we will look up the fqdn
// and if any of the ip addresses in response to the lookup match any 'ignore destinations' prefix we will
// return a dns response that contains the ip addresses we discovered with the lookup (ie not the
// natc behavior, which would return a dummy ip address pointing at natc).
ignoreDsts *bart.Table[bool]
}
// v6ULA is the ULA prefix used by the app connector to assign IPv6 addresses.
@ -192,6 +221,26 @@ func (c *connector) serveDNS() {
}
}
func lookupDestinationIP(domain string) ([]netip.Addr, error) {
netIPs, err := net.LookupIP(domain)
if err != nil {
var dnsError *net.DNSError
if errors.As(err, &dnsError) && dnsError.IsNotFound {
return nil, nil
} else {
return nil, err
}
}
var addrs []netip.Addr
for _, ip := range netIPs {
a, ok := netip.AddrFromSlice(ip)
if ok {
addrs = append(addrs, a)
}
}
return addrs, nil
}
// handleDNS handles a DNS request to the app connector.
// It generates a response based on the request and the node that sent it.
//
@ -219,11 +268,44 @@ func (c *connector) handleDNS(pc net.PacketConn, buf []byte, remoteAddr *net.UDP
return
}
// If there are destination ips that we don't want to route, we
// have to do a dns lookup here to find the destination ip.
if c.ignoreDsts != nil {
if len(msg.Questions) > 0 {
q := msg.Questions[0]
switch q.Type {
case dnsmessage.TypeAAAA, dnsmessage.TypeA:
dstAddrs, err := lookupDestinationIP(q.Name.String())
if err != nil {
log.Printf("HandleDNS: lookup destination failed: %v\n ", err)
return
}
if c.ignoreDestination(dstAddrs) {
bs, err := dnsResponse(&msg, dstAddrs)
// TODO (fran): treat as SERVFAIL
if err != nil {
log.Printf("HandleDNS: generate ignore response failed: %v\n", err)
return
}
_, err = pc.WriteTo(bs, remoteAddr)
if err != nil {
log.Printf("HandleDNS: write failed: %v\n", err)
}
return
}
}
}
}
// None of the destination IP addresses match an ignore destination prefix, do
// the natc thing.
resp, err := c.generateDNSResponse(&msg, who.Node.ID)
// TODO (fran): treat as SERVFAIL
if err != nil {
log.Printf("HandleDNS: connector handling failed: %v\n", err)
return
}
// TODO (fran): treat as NXDOMAIN
if len(resp) == 0 {
return
}
@ -244,6 +326,23 @@ var tsMBox = dnsmessage.MustNewName("support.tailscale.com.")
// argument is the NodeID of the node that sent the request.
func (c *connector) generateDNSResponse(req *dnsmessage.Message, from tailcfg.NodeID) ([]byte, error) {
pm, _ := c.perPeerMap.LoadOrStore(from, &perPeerState{c: c})
var addrs []netip.Addr
if len(req.Questions) > 0 {
switch req.Questions[0].Type {
case dnsmessage.TypeAAAA, dnsmessage.TypeA:
var err error
addrs, err = pm.ipForDomain(req.Questions[0].Name.String())
if err != nil {
return nil, err
}
}
}
return dnsResponse(req, addrs)
}
// dnsResponse makes a DNS response for the natc. If the dnsmessage is requesting TypeAAAA
// or TypeA the provided addrs of the requested type will be used.
func dnsResponse(req *dnsmessage.Message, addrs []netip.Addr) ([]byte, error) {
b := dnsmessage.NewBuilder(nil,
dnsmessage.Header{
ID: req.Header.ID,
@ -265,51 +364,44 @@ func (c *connector) generateDNSResponse(req *dnsmessage.Message, from tailcfg.No
if err := b.StartAnswers(); err != nil {
return nil, err
}
var err error
switch q.Type {
case dnsmessage.TypeAAAA, dnsmessage.TypeA:
var addrs []netip.Addr
addrs, err = pm.ipForDomain(q.Name.String())
if err != nil {
return nil, err
}
want6 := q.Type == dnsmessage.TypeAAAA
found := false
for _, ip := range addrs {
if want6 != ip.Is6() {
continue
}
found = true
if want6 {
err = b.AAAAResource(
if err := b.AAAAResource(
dnsmessage.ResourceHeader{Name: q.Name, Class: q.Class, TTL: 5},
dnsmessage.AAAAResource{AAAA: ip.As16()},
)
); err != nil {
return nil, err
}
} else {
err = b.AResource(
if err := b.AResource(
dnsmessage.ResourceHeader{Name: q.Name, Class: q.Class, TTL: 5},
dnsmessage.AResource{A: ip.As4()},
)
); err != nil {
return nil, err
}
}
break
}
if !found {
err = errors.New("no address found")
}
case dnsmessage.TypeSOA:
err = b.SOAResource(
if err := b.SOAResource(
dnsmessage.ResourceHeader{Name: q.Name, Class: q.Class, TTL: 120},
dnsmessage.SOAResource{NS: q.Name, MBox: tsMBox, Serial: 2023030600,
Refresh: 120, Retry: 120, Expire: 120, MinTTL: 60},
)
); err != nil {
return nil, err
}
case dnsmessage.TypeNS:
err = b.NSResource(
if err := b.NSResource(
dnsmessage.ResourceHeader{Name: q.Name, Class: q.Class, TTL: 120},
dnsmessage.NSResource{NS: tsMBox},
)
}
if err != nil {
return nil, err
); err != nil {
return nil, err
}
}
return b.Finish()
}
@ -345,6 +437,17 @@ func (c *connector) handleTCPFlow(src, dst netip.AddrPort) (handler func(net.Con
}, true
}
// ignoreDestination reports whether any of the provided dstAddrs match the prefixes configured
// in --ignore-destinations
func (c *connector) ignoreDestination(dstAddrs []netip.Addr) bool {
for _, a := range dstAddrs {
if _, ok := c.ignoreDsts.Get(a); ok {
return true
}
}
return false
}
func proxyTCPConn(c net.Conn, dest string) {
addrPortStr := c.LocalAddr().String()
_, port, err := net.SplitHostPort(addrPortStr)

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