1 files changed, 52 insertions, 3 deletions

diff --git a/sd_login/type_machine.go b/sd_login/type_machine.go
index 5892017..d89eaad 100644
--- a/sd_login/type_machine.go
+++ b/sd_login/type_machine.go
@@ -1,4 +1,4 @@
-// Copyright (C) 2016 Luke Shumaker <lukeshu@sbcglobal.net>
+// Copyright (C) 2016-2017 Luke Shumaker <lukeshu@sbcglobal.net>
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -21,9 +21,44 @@ import (
 	"golang.org/x/sys/unix"
 )
 
+// A Machine is a name representing a locally running container or
+// virtual machine that is registerd with (systemd-)machined.
 type Machine string
 
-// running VMs/containers
+// isValid returns whether the Machine name is valid.
+func (m Machine) isValid() bool {
+	if len(m) > host_name_max {
+		// Note that Linux HOST_NAME_MAX is 64, but DNS allows
+		// 255, so names from DNS might be invalid.
+		return false
+	}
+
+	n_dots := 0
+	dot := true
+	for _, c := range m {
+		if c == '.' {
+			if dot {
+				return false
+			}
+			dot = true
+			n_dots++
+		} else {
+			if !strings.ContainsRune(letters+digits+"-_.", c) {
+				return false
+			}
+			dot = false
+		}
+	}
+
+	if dot { // trailing dot or empty
+		return false
+	}
+
+	return true
+}
+
+// GetMachines returns a list of currently running containers/virtual
+// machines.
 func GetMachines() ([]Machine, error) {
 	strs, err := get_files_in_directory("/run/systemd/machines/")
 	if err != nil {
@@ -31,7 +66,8 @@ func GetMachines() ([]Machine, error) {
 	}
 	var machines []Machine
 	for _, str := range strs {
-		if strings.HasPrefix(str, "unit:") || !valid_machine_name(str) {
+		machine := Machine(str)
+		if strings.HasPrefix(str, "unit:") || machine.isValid() {
 			continue
 		}
 		machines = append(machines, Machine(str))
@@ -39,7 +75,14 @@ func GetMachines() ([]Machine, error) {
 	return machines, nil
 }
 
+// GetClass returns the class of a locally running machine.  The class
+// is either "vm" or "container", depending on if the machine is an
+// virtual machine or a container.
 func (m Machine) GetClass() (string, error) {
+	if !m.isValid() {
+		return "", unix.EINVAL
+	}
+
 	env, err := parse_env_file("/run/systemd/machines/" + string(m))
 	if err != nil {
 		return "", err
@@ -51,7 +94,13 @@ func (m Machine) GetClass() (string, error) {
 	return class, nil
 }
 
+// GetIfIndices returns the numeric indices of the network interfaces
+// on the host that are pointing toward this machine.
 func (m Machine) GetIfIndices() ([]int, error) {
+	if !m.isValid() {
+		return nil, unix.EINVAL
+	}
+
 	env, err := parse_env_file("/run/systemd/machines/" + string(m))
 	if err != nil {
 		return nil, err