added generic user lookup and foreground processes

example/port80.go

@@ -13,6 +13,7 @@ func main() {
 	cfg := godrop.Config{
 		User:       "nobody",
 		Group:      "nobody",
+		Foreground: true,
 	}
 	err := godrop.Drop(cfg, func() (net.Listener, error) { return net.Listen("tcp", ":80") })
 	if err != nil {

example/port80and443.go

@@ -13,6 +13,7 @@ func main() {
 	cfg := godrop.Config{
 		User:       "nobody",
 		Group:      "nobody",
+		Foreground: true,
 	}
 	err := godrop.MultiDrop(cfg, func() ([]net.Listener, error) {
 		l1, err := net.Listen("tcp", ":80")

godrop.go

@@ -6,12 +6,10 @@ package godrop
 import (
 	"errors"
 	"fmt"
-	"io/ioutil"
 	"net"
 	"os"
 	"os/exec"
-	"regexp"
+	"os/signal"
-	"strconv"
 	"syscall"
 )
 
@@ -19,47 +17,20 @@ func errf(err error) error {
 	return fmt.Errorf("godrop: %s", err)
 }
 
-func readFile(name, file string) (id int, err error) {
-	id = -1
-	if name == "" {
-		return
-	}
-	f, err := os.Open(file)
-	if err != nil {
-		return
-	}
-	b, err := ioutil.ReadAll(f)
-	if err != nil {
-		return
-	}
-	r := regexp.MustCompile(name + ":.*:(\\d+)")
-	m := r.FindAllStringSubmatch(string(b), 1)
-	if len(m) == 1 {
-		if len(m[0]) == 2 {
-			return strconv.Atoi(m[0][1])
-		}
-	}
-	return
-}
-
-// UID of user
-func UID(user string) (int, error) {
-	return readFile(user, "/etc/passwd")
-}
-
-// GID of group
-func GID(group string) (int, error) {
-	return readFile(group, "/etc/group")
-}
-
 // Config represents the drop config
 type Config struct {
+	// User is the user to drop privileges to.
 	User string
+	// Group is the group to drop privileges to.
 	Group string
+	// Chroot is the directory to chroot into. Leave this emptry for no chroot.
+	// When running on linux, make sure the chroot directory contains the /etc/passwd and /etc/group files.
 	Chroot string
+	// Set to true, to run the process in the foreground.
+	Foreground bool
 }
 
-// Drop will spawn a new process, hand over the listening socket file descriptor and terminate itself after
+// Drop will spawn a new process and hand over the listening socket file descriptor
 func Drop(c Config, f func() (net.Listener, error)) error {
 	return MultiDrop(c, func() ([]net.Listener, error) {
 		l, err := f()
@@ -67,16 +38,16 @@ func Drop(c Config, f func() (net.Listener, error)) error {
 	})
 }
 
-// MultiDrop will spawn a new process, hand over the all listening sockets and terminate itself after
+// MultiDrop will spawn a new process and hand over the all listening sockets
 func MultiDrop(c Config, f func() ([]net.Listener, error)) error {
-	uid, err := UID(c.User)
+	uid, err := userID(c.User)
 	if err != nil {
 		return errf(err)
 	}
 	if uid == 0 {
 		return errf(errors.New("unable to drop privileges to uid 0 (root)"))
 	}
-	gid, err := GID(c.Group)
+	gid, err := groupID(c.Group)
 	if err != nil {
 		return errf(err)
 	}
@@ -105,6 +76,12 @@ func MultiDrop(c Config, f func() ([]net.Listener, error)) error {
 			cmd.ExtraFiles = append(cmd.ExtraFiles, f)
 		}
 
+		if c.Foreground {
+			cmd.Stdin = os.Stdin
+			cmd.Stdout = os.Stdout
+			cmd.Stderr = os.Stderr
+		}
+
 		cmd.SysProcAttr = &syscall.SysProcAttr{
 			Chroot: c.Chroot,
 			Credential: &syscall.Credential{
@@ -118,6 +95,16 @@ func MultiDrop(c Config, f func() ([]net.Listener, error)) error {
 			return errf(err)
 		}
 
+		if c.Foreground {
+			go func() {
+				sigs := make(chan os.Signal)
+				signal.Notify(sigs, syscall.SIGHUP, syscall.SIGINT, syscall.SIGTERM, syscall.SIGQUIT)
+				sig := <-sigs
+				cmd.Process.Signal(sig)
+			}()
+			_ = cmd.Wait()
+			os.Exit(int(cmd.ProcessState.Sys().(syscall.WaitStatus)))
+		}
 		cmd.Process.Release()
 		os.Exit(0)
 	case uid:

lookup.go

@@ -0,0 +1,29 @@
+// Copyright (C) 2017 Marius Schellenberger
+
+package godrop
+
+import "strconv"
+
+func atoi(a string) (int, error) {
+	i, err := strconv.Atoi(a)
+	if err != nil {
+		return -1, err
+	}
+	return i, nil
+}
+
+func userID(username string) (uid int, err error) {
+	id, err := lookupUID(username)
+	if err != nil {
+		return -1, err
+	}
+	return atoi(id)
+}
+
+func groupID(name string) (int, error) {
+	id, err := lookupGID(name)
+	if err != nil {
+		return -1, err
+	}
+	return atoi(id)
+}

lookup_cgo.go

@@ -0,0 +1,23 @@
+// Copyright (C) 2017 Marius Schellenberger
+
+// +build cgo
+
+package godrop
+
+import "os/user"
+
+func lookupUID(username string) (string, error) {
+	u, err := user.Lookup(username)
+	if err != nil {
+		return "", err
+	}
+	return u.Uid, err
+}
+
+func lookupGID(name string) (string, error) {
+	g, err := user.LookupGroup(name)
+	if err != nil {
+		return "", err
+	}
+	return g.Gid, err
+}

lookup_nocgo.go

@@ -0,0 +1,43 @@
+// Copyright (C) 2017 Marius Schellenberger
+
+// +build darwin dragonfly freebsd android linux netbsd openbsd solaris
+// +build !cgo
+
+package godrop
+
+import (
+	"io/ioutil"
+	"os"
+	"regexp"
+)
+
+func readFile(name, file string) (id string, err error) {
+	id = "-1"
+	if name == "" {
+		return
+	}
+	f, err := os.Open(file)
+	if err != nil {
+		return
+	}
+	b, err := ioutil.ReadAll(f)
+	if err != nil {
+		return
+	}
+	r := regexp.MustCompile(name + ":.*:(\\d+)")
+	m := r.FindAllStringSubmatch(string(b), 1)
+	if len(m) == 1 {
+		if len(m[0]) == 2 {
+			return m[0][1], nil
+		}
+	}
+	return
+}
+
+func lookupUID(username string) (string, error) {
+	return readFile(username, "/etc/passwd")
+}
+
+func lookupGID(name string) (string, error) {
+	return readFile(name, "/etc/group")
+}

lookup_test.go

@@ -4,8 +4,8 @@ package godrop
 
 import "testing"
 
-func TestUID(t *testing.T) {
+func TestUserID(t *testing.T) {
-	uid, err := UID("root")
+	uid, err := userID("root")
 	if err != nil {
 		t.Error(err)
 	}
@@ -14,8 +14,8 @@ func TestUID(t *testing.T) {
 	}
 }
 
-func TestGID(t *testing.T) {
+func TestGroupID(t *testing.T) {
-	gid, err := GID("root")
+	gid, err := groupID("root")
 	if err != nil {
 		t.Error(err)
 	}