cmd/create, cmd/run, cmd/utils: Unbreak overriding the HOME variable

The POSIX shell implementation used to read and respect the HOME
environment variable.  It broke when the Go implementation started using
user.Current() [1], because it uses getpwuid_r(3), which only uses the
GNU Name Service Switch's (or NSS') password database and ignores HOME.

This created a strange situation where the toolbox(1) binary ignored the
HOME environment variable, while the profile.d/toolbox.sh shell start-up
snippet and Podman read and respected it.

Restoring the HOME environment variable will enable users to create
Toolbx containers with different home directories from the host for
increased isolation, and to isolate the host's HOME from the system
tests.

Fallout from e8d7f25e83

[1] https://pkg.go.dev/os/user#Current

https://github.com/containers/toolbox/issues/1044
https://github.com/containers/toolbox/issues/1564

src/cmd/create.go

@@ -1,5 +1,5 @@
 /*
- * Copyright © 2019 – 2024 Red Hat Inc.
+ * Copyright © 2019 – 2025 Red Hat Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -300,12 +300,13 @@ func createContainer(container, image, release, authFile string, showCommandToEn
 
 	dbusSystemSocketMountArg := dbusSystemSocket + ":" + dbusSystemSocket
 
-	homeDirEvaled, err := filepath.EvalSymlinks(currentUser.HomeDir)
+	currentUserHomeDir := getCurrentUserHomeDir()
+	homeDirEvaled, err := filepath.EvalSymlinks(currentUserHomeDir)
 	if err != nil {
-		return fmt.Errorf("failed to canonicalize %s", currentUser.HomeDir)
+		return fmt.Errorf("failed to canonicalize %s", currentUserHomeDir)
 	}
 
-	logrus.Debugf("%s canonicalized to %s", currentUser.HomeDir, homeDirEvaled)
+	logrus.Debugf("%s canonicalized to %s", currentUserHomeDir, homeDirEvaled)
 	homeDirMountArg := homeDirEvaled + ":" + homeDirEvaled + ":rslave"
 
 	var avahiSocketMount []string
@@ -412,7 +413,7 @@ func createContainer(container, image, release, authFile string, showCommandToEn
 		"toolbox", "--log-level", "debug",
 		"init-container",
 		"--gid", currentUser.Gid,
-		"--home", currentUser.HomeDir,
+		"--home", currentUserHomeDir,
 		"--shell", userShell,
 		"--uid", currentUser.Uid,
 		"--user", currentUser.Username,

src/cmd/run.go

@@ -448,7 +448,7 @@ func runCommandWithFallbacks(container string,
 
 					workDir = runFallbackWorkDirs[runFallbackWorkDirsIndex]
 					if workDir == "" {
-						workDir = currentUser.HomeDir
+						workDir = getCurrentUserHomeDir()
 					}
 
 					fmt.Fprintf(os.Stderr, "Using %s instead.\n", workDir)

src/cmd/utils.go

@@ -341,6 +341,22 @@ func getCDIFileForNvidia(targetUser *user.User) (string, error) {
 	return cdiFile, nil
 }
 
+func getCurrentUserHomeDir() string {
+	if currentUser == nil {
+		panic("current user unknown")
+	}
+
+	userHomeDir, err := os.UserHomeDir()
+	if err == nil {
+		return userHomeDir
+	}
+
+	logrus.Debugf("Getting the current user's home directory: failed to use os.UserHomeDir(): %s", err)
+	logrus.Debug("Using user.Current() instead")
+
+	return currentUser.HomeDir
+}
+
 func getUsageForCommonCommands() string {
 	var builder strings.Builder
 	builder.WriteString("create    Create a new Toolbx container\n")