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wgengine: diagnose why CreateTUN might've failed for users

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Fixes #273

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This commit is contained in:
Brad Fitzpatrick 2020-04-10 13:44:08 -07:00 committed by Brad Fitzpatrick
parent 3a3b64301e
commit a55c4217db
1 changed files with 71 additions and 3 deletions
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74
wgengine/userspace.go
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@ -12,6 +12,9 @@
"io"
"log"
"net"
"os"
"os/exec"
"runtime"
"strings"
"sync"
"time"
@ -75,15 +78,15 @@ func NewFakeUserspaceEngine(logf logger.Logf, listenPort uint16) (Engine, error)
// NewUserspaceEngine creates the named tun device and returns a Tailscale Engine
// running on it.
func NewUserspaceEngine(logf logger.Logf, tunname string, listenPort uint16) (Engine, error) {
logf("Starting userspace wireguard engine.")
logf("external packet routing via --tun=%s enabled", tunname)
if tunname == "" {
return nil, fmt.Errorf("--tun name must not be blank")
}
logf("Starting userspace wireguard engine with tun device %q", tunname)
tundev, err := tun.CreateTUN(tunname, device.DefaultMTU)
if err != nil {
diagnoseTUNFailure(logf)
logf("CreateTUN: %v\n", err)
return nil, err
}
@ -686,3 +689,68 @@ func (e *userspaceEngine) UpdateStatus(sb *ipnstate.StatusBuilder) {
e.magicConn.UpdateStatus(sb)
}
// diagnoseTUNFailure is called if tun.CreateTUN fails, to poke around
// the system and log some diagnostic info that might help debug why
// TUN failed. Because TUN's already failed and things the program's
// about to end, we might as well log a lot.
func diagnoseTUNFailure(logf logger.Logf) {
switch runtime.GOOS {
case "linux":
diagnoseLinuxTUNFailure(logf)
default:
logf("no TUN failure diagnostics for OS %q", runtime.GOOS)
}
}
func diagnoseLinuxTUNFailure(logf logger.Logf) {
kernel, err := exec.Command("uname", "-r").Output()
kernel = bytes.TrimSpace(kernel)
if err != nil {
logf("no TUN, and failed to look up kernel version: %v", err)
return
}
logf("Linux kernel version: %s", kernel)
modprobeOut, err := exec.Command("/sbin/modprobe", "tun").CombinedOutput()
if err == nil {
logf("'modprobe tun' successful")
// Either tun is currently loaded, or it's statically
// compiled into the kernel (which modprobe checks
// with /lib/modules/$(uname -r)/modules.builtin)
//
// So if there's a problem at this point, it's
// probably because /dev/net/tun doesn't exist.
const dev = "/dev/net/tun"
if fi, err := os.Stat(dev); err != nil {
logf("tun module loaded in kernel, but %s does not exist", dev)
} else {
logf("%s: %v", dev, fi.Mode())
}
// We failed to find why it failed. Just let our
// caller report the error it got from wireguard-go.
return
}
logf("is CONFIG_TUN enabled in your kernel? `modprobe tun` failed with: %s", modprobeOut)
distro := linuxDistro()
switch distro {
case "debian":
dpkgOut, err := exec.Command("dpkg", "-S", "kernel/drivers/net/tun.ko").CombinedOutput()
if len(bytes.TrimSpace(dpkgOut)) == 0 || err != nil {
logf("tun module not loaded nor found on disk")
return
}
if !bytes.Contains(dpkgOut, kernel) {
logf("kernel/drivers/net/tun.ko found on disk, but not for current kernel; are you in middle of a system update and haven't rebooted? found: %s", dpkgOut)
}
}
}
func linuxDistro() string {
if _, err := os.Stat("/etc/debian_version"); err == nil {
return "debian"
}
return ""
}