Don't rely on XDG_RUNTIME_DIR when running as root

This is one more step towards enabling toolbox(1) to be run as root.
When invoked as 'sudo toolbox' there's no XDG_RUNTIME_DIR available for
the root user. Neither the environment variable nor the directory are
present.

XDG_RUNTIME_DIR is used for two reasons. First, to place the 'lock'
file to synchronize Podman migrations and the initialization stamp
file to synchronize the container's entry point with the user-facing
'enter' command running on the host. Second, it's used to propagate
things like the user D-Bus, Pipewire and Wayland sockets.

The first use-case is important for toolbox(1) itself to work. When
running as root, XDG_RUNTIME_DIR is replaced with /run/toolbox for this
purpose.

The second use-case is mostly ignored because sudo(8) doesn't create
a full-fledged user session. Graphical applications can still work by
connecting to a X11 server over the local abstract socket or the file
system socket in /tmp/.X11-unix.

https://github.com/containers/toolbox/issues/267

src/cmd/create.go

@@ -191,9 +191,23 @@ func createContainer(container, image, release string, showCommandToEnter bool)
 	toolboxPathEnvArg := "TOOLBOX_PATH=" + toolboxPath
 	toolboxPathMountArg := toolboxPath + ":/usr/bin/toolbox:ro"
 
+	var runtimeDirectory string
+	var xdgRuntimeDirEnv []string
+
+	if currentUser.Uid == "0" {
+		runtimeDirectory, err = utils.GetRuntimeDirectory(currentUser)
+		if err != nil {
+			return err
+		}
+	} else {
 		xdgRuntimeDir := os.Getenv("XDG_RUNTIME_DIR")
 		xdgRuntimeDirEnvArg := "XDG_RUNTIME_DIR=" + xdgRuntimeDir
-	xdgRuntimeDirMountArg := xdgRuntimeDir + ":" + xdgRuntimeDir
+		xdgRuntimeDirEnv = []string{"--env", xdgRuntimeDirEnvArg}
+
+		runtimeDirectory = xdgRuntimeDir
+	}
+
+	runtimeDirectoryMountArg := runtimeDirectory + ":" + runtimeDirectory
 
 	logrus.Debug("Checking if 'podman create' supports '--mount type=devpts'")
 
@@ -337,12 +351,16 @@ func createContainer(container, image, release string, showCommandToEnter bool)
 		"create",
 		"--dns", "none",
 		"--env", toolboxPathEnvArg,
-		"--env", xdgRuntimeDirEnvArg,
+	}
+
+	createArgs = append(createArgs, xdgRuntimeDirEnv...)
+
+	createArgs = append(createArgs, []string{
 		"--hostname", "toolbox",
 		"--ipc", "host",
 		"--label", "com.github.containers.toolbox=true",
 		"--label", "com.github.debarshiray.toolbox=true",
-	}
+	}...)
 
 	createArgs = append(createArgs, devPtsMount...)
 
@@ -370,7 +388,7 @@ func createContainer(container, image, release string, showCommandToEnter bool)
 		"--volume", homeDirMountArg,
 		"--volume", toolboxPathMountArg,
 		"--volume", usrMountArg,
-		"--volume", xdgRuntimeDirMountArg,
+		"--volume", runtimeDirectoryMountArg,
 	}...)
 
 	createArgs = append(createArgs, kcmSocketMount...)

src/cmd/initContainer.go

@@ -23,6 +23,7 @@ import (
 	"os"
 	"os/user"
 	"path/filepath"
+	"strconv"
 	"strings"
 	"time"
 
@@ -127,15 +128,7 @@ func initContainer(cmd *cobra.Command, args []string) error {
 		return errors.New(errMsg)
 	}
 
-	runtimeDirectory := os.Getenv("XDG_RUNTIME_DIR")
-	if runtimeDirectory == "" {
-		logrus.Debug("XDG_RUNTIME_DIR is unset")
-
-		runtimeDirectory = fmt.Sprintf("/run/user/%d", initContainerFlags.uid)
-		os.Setenv("XDG_RUNTIME_DIR", runtimeDirectory)
-
-		logrus.Debugf("XDG_RUNTIME_DIR set to %s", runtimeDirectory)
-	}
+	utils.EnsureXdgRuntimeDirIsSet(initContainerFlags.uid)
 
 	logrus.Debug("Creating /run/.toolboxenv")
 
@@ -285,16 +278,15 @@ func initContainer(cmd *cobra.Command, args []string) error {
 
 	logrus.Debug("Finished initializing container")
 
-	toolboxRuntimeDirectory := runtimeDirectory + "/toolbox"
-	logrus.Debugf("Creating runtime directory %s", toolboxRuntimeDirectory)
-
-	if err := os.MkdirAll(toolboxRuntimeDirectory, 0700); err != nil {
-		return fmt.Errorf("failed to create runtime directory %s", toolboxRuntimeDirectory)
+	uidString := strconv.Itoa(initContainerFlags.uid)
+	targetUser, err := user.LookupId(uidString)
+	if err != nil {
+		return fmt.Errorf("failed to lookup user ID %s: %w", uidString, err)
 	}
 
-	if err := os.Chown(toolboxRuntimeDirectory, initContainerFlags.uid, initContainerFlags.uid); err != nil {
-		return fmt.Errorf("failed to change ownership of the runtime directory %s",
-			toolboxRuntimeDirectory)
+	toolboxRuntimeDirectory, err := utils.GetRuntimeDirectory(targetUser)
+	if err != nil {
+		return err
 	}
 
 	pid := os.Getpid()

src/cmd/root.go

@@ -226,10 +226,9 @@ func migrate() error {
 		return fmt.Errorf("failed to create configuration directory")
 	}
 
-	runtimeDirectory := os.Getenv("XDG_RUNTIME_DIR")
-	toolboxRuntimeDirectory := runtimeDirectory + "/toolbox"
-	if err := os.MkdirAll(toolboxRuntimeDirectory, 0700); err != nil {
-		return fmt.Errorf("failed to create runtime directory %s", toolboxRuntimeDirectory)
+	toolboxRuntimeDirectory, err := utils.GetRuntimeDirectory(currentUser)
+	if err != nil {
+		return err
 	}
 
 	migrateLock := toolboxRuntimeDirectory + "/migrate.lock"

src/cmd/run.go

@@ -238,8 +238,11 @@ func runCommand(container string,
 
 	logrus.Debugf("Waiting for container %s to finish initializing", container)
 
-	runtimeDirectory := os.Getenv("XDG_RUNTIME_DIR")
-	toolboxRuntimeDirectory := runtimeDirectory + "/toolbox"
+	toolboxRuntimeDirectory, err := utils.GetRuntimeDirectory(currentUser)
+	if err != nil {
+		return err
+	}
+
 	initializedStamp := fmt.Sprintf("%s/container-initialized-%d", toolboxRuntimeDirectory, entryPointPID)
 
 	logrus.Debugf("Checking if initialization stamp %s exists", initializedStamp)

src/pkg/utils/utils.go

@@ -22,6 +22,7 @@ import (
 	"os"
 	"os/exec"
 	"os/user"
+	"path"
 	"path/filepath"
 	"regexp"
 	"sort"
@@ -174,6 +175,17 @@ func CreateErrorInvalidRelease(executableBase string) error {
 	return errors.New(errMsg)
 }
 
+func EnsureXdgRuntimeDirIsSet(uid int) {
+	if xdgRuntimeDir, ok := os.LookupEnv("XDG_RUNTIME_DIR"); !ok {
+		logrus.Debug("XDG_RUNTIME_DIR is unset")
+
+		xdgRuntimeDir = fmt.Sprintf("/run/user/%d", uid)
+		os.Setenv("XDG_RUNTIME_DIR", xdgRuntimeDir)
+
+		logrus.Debugf("XDG_RUNTIME_DIR set to %s", xdgRuntimeDir)
+	}
+}
+
 func ForwardToHost() (int, error) {
 	envOptions := GetEnvOptionsForPreservedVariables()
 	toolboxPath := os.Getenv("TOOLBOX_PATH")
@@ -336,6 +348,40 @@ func GetMountOptions(target string) (string, error) {
 	return mountOptions, nil
 }
 
+func GetRuntimeDirectory(targetUser *user.User) (string, error) {
+	uid, err := strconv.Atoi(targetUser.Uid)
+	if err != nil {
+		return "", fmt.Errorf("failed to convert user ID to integer: %w", err)
+	}
+
+	var runtimeDirectory string
+
+	if uid == 0 {
+		runtimeDirectory = "/run"
+	} else {
+		runtimeDirectory = os.Getenv("XDG_RUNTIME_DIR")
+	}
+
+	toolboxRuntimeDirectory := path.Join(runtimeDirectory, "toolbox")
+	logrus.Debugf("Creating runtime directory %s", toolboxRuntimeDirectory)
+
+	if err := os.MkdirAll(toolboxRuntimeDirectory, 0700); err != nil {
+		wrapped_err := fmt.Errorf("failed to create runtime directory %s: %w",
+			toolboxRuntimeDirectory,
+			err)
+		return "", wrapped_err
+	}
+
+	if err := os.Chown(toolboxRuntimeDirectory, uid, uid); err != nil {
+		wrapped_err := fmt.Errorf("failed to change ownership of the runtime directory %s: %w",
+			toolboxRuntimeDirectory,
+			err)
+		return "", wrapped_err
+	}
+
+	return toolboxRuntimeDirectory, nil
+}
+
 // HumanDuration accepts a Unix time value and converts it into a human readable
 // string.
 //