tailscale/net/netns/netns_linux.go

104 lines
2.8 KiB
Go

// 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 netns
import (
"flag"
"fmt"
"os"
"os/exec"
"sync"
"syscall"
"golang.org/x/sys/unix"
"tailscale.com/net/interfaces"
)
// tailscaleBypassMark is the mark indicating that packets originating
// from a socket should bypass Tailscale-managed routes during routing
// table lookups.
//
// Keep this in sync with tailscaleBypassMark in
// wgengine/router/router_linux.go.
const tailscaleBypassMark = 0x80000
// ipRuleOnce is the sync.Once & cached value for ipRuleAvailable.
var ipRuleOnce struct {
sync.Once
v bool
}
// ipRuleAvailable reports whether the 'ip rule' command works.
// If it doesn't, we have to use SO_BINDTODEVICE on our sockets instead.
func ipRuleAvailable() bool {
ipRuleOnce.Do(func() {
ipRuleOnce.v = exec.Command("ip", "rule").Run() == nil
})
return ipRuleOnce.v
}
// ignoreErrors returns true if we should ignore setsocketopt errors in
// this instance.
func ignoreErrors() bool {
// If we're in a test, ignore errors. Assume the test knows
// what it's doing and will do its own skips or permission
// checks if it's setting up a world that needs netns to work.
// But by default, assume that tests don't need netns and it's
// harmless to ignore the sockopts failing.
if flag.CommandLine.Lookup("test.v") != nil {
return true
}
if os.Getuid() != 0 {
// only root can manipulate these socket flags
return true
}
return false
}
// control marks c as necessary to dial in a separate network namespace.
//
// It's intentionally the same signature as net.Dialer.Control
// and net.ListenConfig.Control.
func control(network, address string, c syscall.RawConn) error {
var sockErr error
err := c.Control(func(fd uintptr) {
if ipRuleAvailable() {
sockErr = setBypassMark(fd)
} else {
sockErr = bindToDevice(fd)
}
})
if err != nil {
return fmt.Errorf("RawConn.Control on %T: %w", c, err)
}
if sockErr != nil && ignoreErrors() {
// TODO(bradfitz): maybe log once? probably too spammy for e.g. CLI tools like tailscale netcheck.
return nil
}
return sockErr
}
func setBypassMark(fd uintptr) error {
if err := unix.SetsockoptInt(int(fd), unix.SOL_SOCKET, unix.SO_MARK, tailscaleBypassMark); err != nil {
return fmt.Errorf("setting SO_MARK bypass: %w", err)
}
return nil
}
func bindToDevice(fd uintptr) error {
ifc, err := interfaces.DefaultRouteInterface()
if err != nil {
// Make sure we bind to *some* interface,
// or we could get a routing loop.
// "lo" is always wrong, but if we don't have
// a default route anyway, it doesn't matter.
ifc = "lo"
}
if err := unix.SetsockoptString(int(fd), unix.SOL_SOCKET, unix.SO_BINDTODEVICE, ifc); err != nil {
return fmt.Errorf("setting SO_BINDTODEVICE: %w", err)
}
return nil
}