added generic user lookup and foreground processes

godrop.go

@@ -6,12 +6,10 @@ package godrop
 import (
 	"errors"
 	"fmt"
-	"io/ioutil"
 	"net"
 	"os"
 	"os/exec"
-	"regexp"
-	"strconv"
+	"os/signal"
 	"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   string
-	Group  string
+	// 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: