simplified library and added better examples and net.UnixListener support

godrop.go

@@ -1,7 +1,11 @@
+// Copyright (C) 2017 Marius Schellenberger
+
+// Package godrop provides a simple privileges dropping library
 package godrop
 
 import (
 	"errors"
+	"fmt"
 	"io/ioutil"
 	"net"
 	"os"
@@ -11,6 +15,10 @@ import (
 	"syscall"
 )
 
+func errf(err error) error {
+	return fmt.Errorf("godrop: %s", err)
+}
+
 func readFile(name, file string) (id int, err error) {
 	id = -1
 	if name == "" {
@@ -44,6 +52,7 @@ func GID(group string) (int, error) {
 	return readFile(group, "/etc/group")
 }
 
+// Config represents the drop config
 type Config struct {
 	User   string
 	Group  string
@@ -52,78 +61,43 @@ type Config struct {
 
 // Drop will spawn a new process, hand over the listening socket file descriptor and terminate itself after
 func Drop(c Config, f func() (net.Listener, error)) error {
-	uid, err := UID(c.User)
-	if err != nil {
-		return err
-	}
-	gid, err := GID(c.Group)
-	if err != nil {
-		return err
-	}
-	switch os.Getuid() {
-	case 0:
-		ln, err := f()
-		if err != nil {
-			return err
-		}
-
-		l, ok := ln.(*net.TCPListener)
-		if !ok {
-			return errors.New("godrop: interface conversion failed")
-		}
-		f, err := l.File()
-		if err != nil {
-			return err
-		}
-
-		cmd := exec.Command(os.Args[0], os.Args[1:]...)
-		cmd.ExtraFiles = []*os.File{f}
-		cmd.SysProcAttr = &syscall.SysProcAttr{
-			Chroot: c.Chroot,
-			Credential: &syscall.Credential{
-				Uid: uint32(uid),
-				Gid: uint32(gid),
-			},
-			Setsid: true,
-		}
-
-		if err := cmd.Start(); err != nil {
-			return err
-		}
-
-		cmd.Process.Release()
-		os.Exit(0)
-	case uid:
-		return nil
-	}
-	return errors.New("godrop: droping priviledges failed")
+	return MultiDrop(c, func() ([]net.Listener, error) {
+		l, err := f()
+		return []net.Listener{l}, err
+	})
 }
 
 // MultiDrop will spawn a new process, hand over the all listening sockets and terminate itself after
 func MultiDrop(c Config, f func() ([]net.Listener, error)) error {
 	uid, err := UID(c.User)
 	if err != nil {
-		return err
+		return errf(err)
 	}
 	gid, err := GID(c.Group)
 	if err != nil {
-		return err
+		return errf(err)
 	}
 	switch os.Getuid() {
 	case 0:
 		cmd := exec.Command(os.Args[0], os.Args[1:]...)
 		ln, err := f()
 		if err != nil {
-			return err
+			return errf(err)
 		}
-		for _, v := range ln {
-			l, ok := v.(*net.TCPListener)
-			if !ok {
-				return errors.New("godrop: interface conversion failed")
+		for i, v := range ln {
+			var f *os.File
+			switch l := v.(type) {
+			case *net.TCPListener:
+				f, err = l.File()
+				l.Close()
+			case *net.UnixListener:
+				f, err = l.File()
+				l.Close()
+			default:
+				return errf(fmt.Errorf("index: %d listener is not type of either *net.TCPListener or *net.UnixListener", i))
 			}
-			f, err := l.File()
 			if err != nil {
-				return err
+				return errf(fmt.Errorf("index: %d %s", i, err))
 			}
 			cmd.ExtraFiles = append(cmd.ExtraFiles, f)
 		}
@@ -138,7 +112,7 @@ func MultiDrop(c Config, f func() ([]net.Listener, error)) error {
 		}
 
 		if err := cmd.Start(); err != nil {
-			return err
+			return errf(err)
 		}
 
 		cmd.Process.Release()
@@ -146,15 +120,17 @@ func MultiDrop(c Config, f func() ([]net.Listener, error)) error {
 	case uid:
 		return nil
 	}
-	return errors.New("godrop: droping priviledges failed")
+	return errf(errors.New("dropping priviledges failed"))
 }
 
 // GetListener returns the listener socket of file descriptor 3
 func GetListener() (net.Listener, error) {
-	return net.FileListener(os.NewFile(3, "[socket]"))
+	return GetListenerFd(3)
 }
 
 // GetListenerFd returns the listener socket of the given file descriptor
 func GetListenerFd(fd int) (net.Listener, error) {
-	return net.FileListener(os.NewFile(uintptr(fd), "[socket]"))
+	f := os.NewFile(uintptr(fd), "")
+	defer f.Close()
+	return net.FileListener(f)
 }