wgengine/router: add Plan 9 implementation

Updates #5794

Change-Id: Ib78a3ea971a2374d405b024ab88658ec34be59a6
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

3 files changed, 162 insertions, 1 deletions

diff --git a/ipn/ipnlocal/local.go b/ipn/ipnlocal/local.go
index c44827aa4..7d69b884d 100644
--- a/ipn/ipnlocal/local.go
+++ b/ipn/ipnlocal/local.go
@@ -5069,6 +5069,11 @@ func shouldUseOneCGNATRoute(logf logger.Logf, mon *netmon.Monitor, controlKnobs
 		}
 	}
 
+	if versionOS == "plan9" {
+		// Just temporarily during plan9 bringup to have fewer routes to debug.
+		return true
+	}
+
 	// Also prefer to do this on the Mac, so that we don't need to constantly
 	// update the network extension configuration (which is disruptive to
 	// Chrome, see https://github.com/tailscale/tailscale/issues/3102). Only
diff --git a/wgengine/router/router_default.go b/wgengine/router/router_default.go
index 1e675d1fc..8dcbd36d0 100644
--- a/wgengine/router/router_default.go
+++ b/wgengine/router/router_default.go
@@ -1,7 +1,7 @@
 // Copyright (c) Tailscale Inc & AUTHORS
 // SPDX-License-Identifier: BSD-3-Clause
 
-//go:build !windows && !linux && !darwin && !openbsd && !freebsd
+//go:build !windows && !linux && !darwin && !openbsd && !freebsd && !plan9
 
 package router
 
diff --git a/wgengine/router/router_plan9.go b/wgengine/router/router_plan9.go
new file mode 100644
index 000000000..7ed7686d9
--- /dev/null
+++ b/wgengine/router/router_plan9.go
@@ -0,0 +1,156 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+package router
+
+import (
+	"bufio"
+	"bytes"
+	"fmt"
+	"net/netip"
+	"os"
+	"strings"
+
+	"github.com/tailscale/wireguard-go/tun"
+	"tailscale.com/health"
+	"tailscale.com/net/netmon"
+	"tailscale.com/types/logger"
+)
+
+func newUserspaceRouter(logf logger.Logf, tundev tun.Device, netMon *netmon.Monitor, health *health.Tracker) (Router, error) {
+	r := &plan9Router{
+		logf:   logf,
+		tundev: tundev,
+		netMon: netMon,
+	}
+	cleanAllTailscaleRoutes(logf)
+	return r, nil
+}
+
+type plan9Router struct {
+	logf   logger.Logf
+	tundev tun.Device
+	netMon *netmon.Monitor
+	health *health.Tracker
+}
+
+func (r *plan9Router) Up() error {
+	return nil
+}
+
+func (r *plan9Router) Set(cfg *Config) error {
+	if cfg == nil {
+		cleanAllTailscaleRoutes(r.logf)
+		return nil
+	}
+
+	var self4, self6 netip.Addr
+	for _, addr := range cfg.LocalAddrs {
+		ctl := r.tundev.File()
+		maskBits := addr.Bits()
+		if addr.Addr().Is4() {
+			// The mask sizes in Plan9 are in IPv6 bits, even for IPv4.
+			maskBits += (128 - 32)
+			self4 = addr.Addr()
+		}
+		if addr.Addr().Is6() {
+			self6 = addr.Addr()
+		}
+		_, err := fmt.Fprintf(ctl, "add %s /%d\n", addr.Addr().String(), maskBits)
+		r.logf("route/plan9: add %s /%d = %v", addr.Addr().String(), maskBits, err)
+	}
+
+	ipr, err := os.OpenFile("/net/iproute", os.O_RDWR, 0)
+	if err != nil {
+		return fmt.Errorf("open /net/iproute: %w", err)
+	}
+	defer ipr.Close()
+
+	// TODO(bradfitz): read existing routes, delete ones tagged "tail"
+	// that aren't in cfg.LocalRoutes.
+
+	if _, err := fmt.Fprintf(ipr, "tag tail\n"); err != nil {
+		return fmt.Errorf("tag tail: %w", err)
+	}
+
+	for _, route := range cfg.Routes {
+		maskBits := route.Bits()
+		if route.Addr().Is4() {
+			// The mask sizes in Plan9 are in IPv6 bits, even for IPv4.
+			maskBits += (128 - 32)
+		}
+		var nextHop netip.Addr
+		if route.Addr().Is4() {
+			nextHop = self4
+		} else if route.Addr().Is6() {
+			nextHop = self6
+		}
+		if !nextHop.IsValid() {
+			r.logf("route/plan9: skipping route %s: no next hop (no self addr)", route.String())
+			continue
+		}
+		r.logf("route/plan9: plan9.router: add %s /%d %s", route.Addr(), maskBits, nextHop)
+		if _, err := fmt.Fprintf(ipr, "add %s /%d %s\n", route.Addr(), maskBits, nextHop); err != nil {
+			return fmt.Errorf("add %s: %w", route.String(), err)
+		}
+	}
+
+	if len(cfg.LocalRoutes) > 0 {
+		r.logf("route/plan9: TODO: Set LocalRoutes %v", cfg.LocalRoutes)
+	}
+	if len(cfg.SubnetRoutes) > 0 {
+		r.logf("route/plan9: TODO: Set SubnetRoutes %v", cfg.SubnetRoutes)
+	}
+
+	return nil
+}
+
+// UpdateMagicsockPort implements the Router interface. This implementation
+// does nothing and returns nil because this router does not currently need
+// to know what the magicsock UDP port is.
+func (r *plan9Router) UpdateMagicsockPort(_ uint16, _ string) error {
+	return nil
+}
+
+func (r *plan9Router) Close() error {
+	// TODO(bradfitz): unbind
+	return nil
+}
+
+func cleanUp(logf logger.Logf, _ string) {
+	cleanAllTailscaleRoutes(logf)
+}
+
+func cleanAllTailscaleRoutes(logf logger.Logf) {
+	routes, err := os.OpenFile("/net/iproute", os.O_RDWR, 0)
+	if err != nil {
+		logf("cleaning routes: %v", err)
+		return
+	}
+	defer routes.Close()
+
+	// Using io.ReadAll or os.ReadFile on /net/iproute fails; it results in a
+	// 511 byte result when the actual /net/iproute contents are over 1k.
+	// So do it in one big read instead. Who knows.
+	routeBuf := make([]byte, 1<<20)
+	n, err := routes.Read(routeBuf)
+	if err != nil {
+		logf("cleaning routes: %v", err)
+		return
+	}
+	routeBuf = routeBuf[:n]
+
+	bs := bufio.NewScanner(bytes.NewReader(routeBuf))
+	for bs.Scan() {
+		f := strings.Fields(bs.Text())
+		if len(f) < 6 {
+			continue
+		}
+		tag := f[4]
+		if tag != "tail" {
+			continue
+		}
+		_, err := fmt.Fprintf(routes, "remove %s %s\n", f[0], f[1])
+		logf("router: cleaning route %s %s: %v", f[0], f[1], err)
+	}
+}