Allow alternative sudo path for NixOS (#51549)

lib/devicetrust/native/device_linux.go

@@ -271,10 +271,12 @@ func readDMIInfoEscalated() (*linux.DMIInfo, error) {
 		return nil, trace.Wrap(err, "reading current executable")
 	}
 
+	sudo := sudoPath()
+
 	// Run `sudo -v` first to re-authenticate, then run the actual tsh command
 	// using `sudo --non-interactive`, so we don't risk getting sudo output
 	// mixed with our desired output.
-	sudoCmd := exec.Command("/usr/bin/sudo", "-v")
+	sudoCmd := exec.Command(sudo, "-v")
 	sudoCmd.Stdout = os.Stdout
 	sudoCmd.Stderr = os.Stderr
 	sudoCmd.Stdin = os.Stdin
@@ -289,7 +291,7 @@ func readDMIInfoEscalated() (*linux.DMIInfo, error) {
 	defer cancel()
 
 	dmiOut := &bytes.Buffer{}
-	dmiCmd := exec.CommandContext(ctx, "/usr/bin/sudo", "-n", tshPath, "device", "dmi-read")
+	dmiCmd := exec.CommandContext(ctx, sudo, "-n", tshPath, "device", "dmi-read")
 	dmiCmd.Stdout = dmiOut
 	if err := dmiCmd.Run(); err != nil {
 		return nil, trace.Wrap(err, "running `sudo tsh device dmi-read`")
@@ -330,3 +332,33 @@ func saveDMIInfoToCache(dmiInfo *linux.DMIInfo) error {
 
 	return nil
 }
+
+func sudoPath() string {
+	const defaultSudoPath = "/usr/bin/sudo"
+
+	for i, path := range []string{
+		defaultSudoPath, // preferred
+
+		// Fallbacks are only allowed if /usr/bin/sudo does not exist.
+		// If it does exist, then it's used regardless of any other errors that may
+		// happen later.
+		"/run/wrappers/bin/sudo", // NixOS
+	} {
+		if _, err := os.Stat(path); err != nil {
+			slog.DebugContext(
+				context.Background(),
+				"Failed to stat sudo binary",
+				"error", err,
+				"path", path,
+			)
+			continue
+		}
+		if i > 0 {
+			slog.DebugContext(context.Background(), "Using alternative sudo path", "path", path)
+		}
+		return path
+	}
+
+	// If everything fails then use the default and hard-fail later.
+	return defaultSudoPath
+}