net/tsaddr: new package to hold Tailscale-specific IPs/ranges

And update existing callers with (near) duplicated cases.

net/tsaddr/tsaddr.go

@@ -0,0 +1,52 @@
+// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package tsaddr handles Tailscale-specific IPs and ranges.
+package tsaddr
+
+import (
+	"sync"
+
+	"inet.af/netaddr"
+)
+
+// ChromeOSVMRange returns the subset of the CGNAT IPv4 range used by
+// ChromeOS to interconnect the host OS to containers and VMs. We
+// avoid allocating Tailscale IPs from it, to avoid conflicts.
+func ChromeOSVMRange() netaddr.IPPrefix {
+	chromeOSRange.Do(func() { mustPrefix(&chromeOSRange.v, "100.115.92.0/23") })
+	return chromeOSRange.v
+}
+
+var chromeOSRange oncePrefix
+
+// CGNATRange returns the Carrier Grade NAT address range that
+// is the superset range that Tailscale assigns out of.
+// See https://tailscale.com/kb/1015/100.x-addresses.
+// Note that Tailscale does not assign out of the ChromeOSVMRange.
+func CGNATRange() netaddr.IPPrefix {
+	cgnatRange.Do(func() { mustPrefix(&cgnatRange.v, "100.64.0.0/10") })
+	return cgnatRange.v
+}
+
+var cgnatRange oncePrefix
+
+// IsTailscaleIP reports whether ip is an IP address in a range that
+// Tailscale assigns from.
+func IsTailscaleIP(ip netaddr.IP) bool {
+	return CGNATRange().Contains(ip) && !ChromeOSVMRange().Contains(ip)
+}
+
+func mustPrefix(v *netaddr.IPPrefix, prefix string) {
+	var err error
+	*v, err = netaddr.ParseIPPrefix(prefix)
+	if err != nil {
+		panic(err)
+	}
+}
+
+type oncePrefix struct {
+	sync.Once
+	v netaddr.IPPrefix
+}

net/tsaddr/tsaddr_test.go

@@ -0,0 +1,19 @@
+// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package tsaddr
+
+import "testing"
+
+func TestChromeOSVMRange(t *testing.T) {
+	if got, want := ChromeOSVMRange().String(), "100.115.92.0/23"; got != want {
+		t.Errorf("got %q; want %q", got, want)
+	}
+}
+
+func TestCGNATRange(t *testing.T) {
+	if got, want := CGNATRange().String(), "100.64.0.0/10"; got != want {
+		t.Errorf("got %q; want %q", got, want)
+	}
+}