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package main
import (
"crypto/tls"
"flag"
"fmt"
"log"
"net"
"os"
"os/exec"
"os/user"
"strconv"
"sync"
"syscall"
)
var (
cfile = flag.String("cert", "cert.pem", "Certificate file in PEM format")
kfile = flag.String("key", "key.pem", "Key file in PEM format")
port = flag.String("port", ":1234", "Port to bind to")
max = flag.Int("max", 5, "Maximum allowed failed attempts from IP")
uid = flag.Int("uid", -1, "UID to run under")
args []string
)
const TLSSERVER = "[tlsserver]"
func main() {
flag.Parse()
if flag.NArg() < 1 {
fmt.Println("Usage: tlsserver [options] cmd [flags for cmd]")
fmt.Println("options:")
flag.PrintDefaults()
os.Exit(1)
}
if os.Args[0] == TLSSERVER {
log.Fatal(serve())
} else {
log.Fatal(exc())
}
}
func exc() error {
if *uid < 0 {
return serve()
}
// Collect information about the user
user, err := user.LookupId(strconv.Itoa(*uid))
if err != nil {
return err
}
// Get the primary and secondary groups
gids := []int{}
gid, err := strconv.Atoi(user.Gid)
if err != nil {
return fmt.Errorf("couldn't parse user.Gid, strconv.Atoi(%s): %v", user.Gid, err)
}
if sgids, err := user.GroupIds(); err != nil {
log.Printf("weird, couldn't get supplimentary groups: %v", err)
} else {
for _, s := range sgids {
v, e := strconv.Atoi(s)
if e != nil {
log.Printf("weird, strconv.Atoi(%s): %v", s, e)
continue
} else if v != gid {
gids = append(gids, v)
}
}
}
if err := setgid(gid); err != nil {
return err
}
if len(gids) > 0 {
if err = syscall.Setgroups(gids); err != nil {
return fmt.Errorf("syscall.Setgroups: %w", err)
}
}
if err = setuid(*uid); err != nil {
return err
}
// Setup the arguments that are needed
args := []string{TLSSERVER} // name of the command
for _, arg := range []string{"cert", "key", "port"} {
fl := flag.Lookup(arg)
// Only set the flag if it's value are different from the default
if fl != nil && fl.Value.String() != fl.DefValue {
args = append(args, "-"+arg, fl.Value.String())
}
}
args = append(args, flag.Args()...)
return syscall.Exec(os.Args[0], args, os.Environ())
}
func serve() error {
args = flag.Args()
// setup certs etc. for TLS-socket
tconf := new(tls.Config)
cert, err := tls.LoadX509KeyPair(*cfile, *kfile)
if err != nil {
fmt.Println("error with certs:", err)
os.Exit(2)
}
tconf.Certificates = append(tconf.Certificates, cert)
tconf.BuildNameToCertificate()
// start listening
sock, err := tls.Listen("tcp", *port, tconf)
if err != nil {
fmt.Println("error with tcp-socket:", err)
os.Exit(3)
}
defer sock.Close()
// accept-loop
for {
conn, err := sock.Accept()
if err != nil {
log.Println("error during Accept()", err)
continue
}
log.Println("Got connection:", conn.RemoteAddr())
go handleConnection(conn, args...)
}
}
// Track the number of bad attempts.
var mux sync.RWMutex
var badActors = map[string]int{}
func isBadActor(host string) bool {
mux.RLock()
defer mux.RUnlock()
if n, ok := badActors[host]; ok && n >= *max {
return true
}
return false
}
func markBadActor(host string) {
mux.Lock()
defer mux.Unlock()
n, _ := badActors[host]
badActors[host] = n + 1
}
func markGoodActor(host string) {
mux.Lock()
defer mux.Unlock()
n, _ := badActors[host]
if n > 0 {
n -= 1
}
badActors[host] = n
}
func handleConnection(conn net.Conn, args ...string) {
defer conn.Close()
// prepare environment according to tcp-environ(5)
rh, rp, err := net.SplitHostPort(conn.RemoteAddr().String())
if err != nil {
log.Println("net.SplitHostPort(conn.RemoteAddr()):", err)
return
}
if isBadActor(rh) {
log.Printf("Too many bad attempts from %s, dropping connection\n", rh)
return
}
lh, lp, err := net.SplitHostPort(conn.LocalAddr().String())
if err != nil {
log.Println("net.SplitHostPort(conn.LocalAddr()):", err)
return
}
// setup cmd
cmd := exec.Command(args[0])
cmd.Args = args
cmd.Stdin = conn
cmd.Stdout = conn
cmd.Stderr = os.Stderr
cmd.Env = []string{
"PATH=" + os.Getenv("PATH"),
"PROTO=TCP",
"TCPLOCALIP=" + lh,
"TCPLOCALPORT=" + lp,
"TCPREMOTEIP=" + rh,
"TCPREMOTEPORT=" + rp,
}
err = cmd.Run()
if err != nil {
log.Println("Cmd error return: ", err)
markBadActor(rh)
} else {
markGoodActor(rh)
}
log.Println("Done with connection", conn.RemoteAddr())
}
// Since go1.4 the setgid syscall is deliberatelly not supported anymore, as it
// only applies to the calling thread. So we try this here:
func setgid(gid int) error {
// RawSyscall(trap, a1, a2, a3 uintptr) (r1, r2 uintptr, err Errno)
_, _, e := syscall.RawSyscall(syscall.SYS_SETGID, uintptr(gid), 0, 0)
if e != 0 {
return fmt.Errorf("setgid: %w", e)
}
return nil
}
func setuid(uid int) error {
// RawSyscall(trap, a1, a2, a3 uintptr) (r1, r2 uintptr, err Errno)
_, _, e := syscall.RawSyscall(syscall.SYS_SETUID, uintptr(uid), 0, 0)
if e != 0 {
return fmt.Errorf("setuid: %w", e)
}
return nil
}
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