builder/chroot: Use ChrootShell() instead of ChrootExecStdin()

With ChrootShell() we can drop usage of the chroot binary, as well as
choose the initial workdir to spawn in to.

As the files are now build as root, they are owned by root so chroot
as root but start at the buildUser home directory.

builder/chroot.go

@@ -66,14 +66,8 @@ func (p *Package) Chroot(notif PidNotifier, pman *EopkgManager, overlay *Overlay
 	// Allow bash to work
 	commands.SetStdin(os.Stdin)
 
-	// Legacy package format requires root, stay as root.
-	user := BuildUser
-	if p.Type == PackageTypeXML {
-		user = "root"
-	}
-
-	loginCommand := fmt.Sprintf("/bin/su - %s -s %s", user, BuildUserShell)
-	err := ChrootExecStdin(notif, overlay.MountPoint, loginCommand)
+	loginCommand := fmt.Sprintf("/bin/su - root -s %s", BuildUserShell)
+	err := ChrootShell(notif, overlay.MountPoint, loginCommand, BuildUserHome)
 
 	commands.SetStdin(nil)
 	notif.SetActivePID(0)

builder/util.go

@@ -231,30 +231,29 @@ func ChrootExecStdin(notif PidNotifier, dir, command string) error {
 }
 
 func ChrootShell(notif PidNotifier, dir, command, workdir string) error {
-
 	// Hold an fd for the og root
 	fd, err := os.Open("/")
 	if err != nil {
 		return err
 	}
 
 	// Remember our working directory
-	wd, err := os.Getwd()
-	if err != nil {
-		return err
+	wd, err2 := os.Getwd()
+	if err2 != nil {
+		return err2
 	}
 
 	// Ensure chroot directory is available
-	if err := os.Chdir(dir); err != nil {
+	if err = os.Chdir(dir); err != nil {
 		return err
 	}
 
-	if err := syscall.Chroot(dir); err != nil {
+	if err = syscall.Chroot(dir); err != nil {
 		fd.Close()
 		return err
 	}
 
-	if err := os.Chdir("/"); err != nil {
+	if err = os.Chdir("/"); err != nil {
 		return err
 	}
 
@@ -267,28 +266,32 @@ func ChrootShell(notif PidNotifier, dir, command, workdir string) error {
 	c.Env = ChrootEnvironment
 	c.Dir = workdir
 
-	if err := c.Start(); err != nil {
+	if err = c.Start(); err != nil {
 		goto CLEANUP
 	}
 
 	notif.SetActivePID(c.Process.Pid)
 
-	if err := c.Wait(); err != nil {
+	if err = c.Wait(); err != nil {
 		goto CLEANUP
 	}
 
 CLEANUP:
 	// Return to our original root and working directory
 	defer fd.Close()
-	if err := fd.Chdir(); err != nil {
+
+	if err = fd.Chdir(); err != nil {
 		return err
 	}
-	if err := syscall.Chroot("."); err != nil {
+
+	if err = syscall.Chroot("."); err != nil {
 		return err
 	}
-	if err := os.Chdir(wd); err != nil {
+
+	if err = os.Chdir(wd); err != nil {
 		return err
 	}
+
 	return err
 }