fix(security): fix sandbox bypass and panic when -sandbox and -python are both set

pkg/httpserver/httpserver.go

@@ -62,7 +62,10 @@ func New(options *Options) (*HTTPServer, error) {
 
 	var httpHandler http.Handler
 	if options.Python {
-		httpHandler = PythonStyle(dir.(http.Dir))
+		// PythonStyle now accepts http.FileSystem so SandboxFileSystem is
+		// honoured when -sandbox is also set (previously a type assertion to
+		// http.Dir would panic at startup when Sandbox=true).
+		httpHandler = PythonStyle(dir)
 	} else {
 		httpHandler = http.FileServer(dir)
 	}

pkg/httpserver/httpserver_security_test.go

@@ -0,0 +1,48 @@
+package httpserver
+
+import (
+	"net/http"
+	"testing"
+)
+
+// TestPythonStyleAcceptFileSystem verifies that PythonStyle accepts an
+// http.FileSystem interface (not a concrete http.Dir).  Before the fix,
+// httpserver.New() panicked with
+//
+//	interface conversion: http.FileSystem is httpserver.SandboxFileSystem, not http.Dir
+//
+// when both -sandbox and -python flags were set, because PythonStyle only
+// accepted http.Dir via a type assertion.
+func TestPythonStyleAcceptFileSystem(t *testing.T) {
+	// SandboxFileSystem implements http.FileSystem but is NOT http.Dir.
+	// Passing it to PythonStyle must not panic.
+	sbfs := SandboxFileSystem{
+		fs:         http.Dir(t.TempDir()),
+		RootFolder: t.TempDir(),
+	}
+	// This call would panic on the old code because of dir.(http.Dir).
+	handler := PythonStyle(sbfs)
+	if handler == nil {
+		t.Fatal("PythonStyle returned nil handler")
+	}
+}
+
+// TestNewServerSandboxPythonNoPanic mirrors the exact code path in New()
+// that used to panic: Sandbox=true + Python=true.
+func TestNewServerSandboxPythonNoPanic(t *testing.T) {
+	dir := t.TempDir()
+	opts := &Options{
+		Folder:        dir,
+		ListenAddress: "127.0.0.1:0",
+		Sandbox:       true,
+		Python:        true,
+	}
+	// Before the fix this returned a panic, not an error.
+	srv, err := New(opts)
+	if err != nil {
+		t.Fatalf("New() returned unexpected error: %v", err)
+	}
+	if srv == nil {
+		t.Fatal("New() returned nil server")
+	}
+}

pkg/httpserver/pythonliststyle.go

@@ -5,8 +5,6 @@ import (
 	"fmt"
 	"io"
 	"net/http"
-	"os"
-	"path/filepath"
 )
 
 const (
@@ -30,7 +28,7 @@ const (
 
 type pythonStyleHandler struct {
 	origWriter http.ResponseWriter
-	root       http.Dir
+	root       http.FileSystem
 }
 
 func (h *pythonStyleHandler) Header() http.Header {
@@ -75,22 +73,33 @@ func (h *pythonStyleHandler) WriteHeader(statusCode int) {
 }
 
 func (h *pythonStyleHandler) ServeHTTP(writer http.ResponseWriter, request *http.Request) {
-	target := filepath.Join(string(h.root), filepath.Clean(request.URL.Path))
-	file, err := os.Stat(target)
+	// Use the FileSystem's Open to respect sandbox containment checks.
+	// This avoids building raw OS paths and correctly delegates to SandboxFileSystem
+	// or any other http.FileSystem implementation.
+	f, err := h.root.Open(request.URL.Path)
+	if err != nil {
+		http.NotFound(writer, request)
+		return
+	}
+	defer f.Close()
 
-	if err != nil || !file.IsDir() {
-		http.ServeFile(writer, request, target)
+	fi, err := f.Stat()
+	if err != nil || !fi.IsDir() {
+		// Not a directory: serve through the FileSystem handler
+		http.FileServer(h.root).ServeHTTP(writer, request)
 		return
-	} else {
-		_, _ = fmt.Fprintf(writer, htmlHeader, request.URL.Path)
-		_, _ = fmt.Fprintf(writer, "<h1>Directory listing for %s</h1>\n<hr>\n", request.URL.Path)
-		h.origWriter = writer
-		http.ServeFile(h, request, target)
-		_, _ = fmt.Fprint(writer, htmlFooter)
 	}
+	_, _ = fmt.Fprintf(writer, htmlHeader, request.URL.Path)
+	_, _ = fmt.Fprintf(writer, "<h1>Directory listing for %s</h1>\n<hr>\n", request.URL.Path)
+	h.origWriter = writer
+	http.FileServer(h.root).ServeHTTP(h, request)
+	_, _ = fmt.Fprint(writer, htmlFooter)
 }
 
-func PythonStyle(root http.Dir) http.Handler {
+// PythonStyle returns an HTTP handler that renders directory listings in Python's
+// SimpleHTTPServer style.  It accepts any http.FileSystem so that sandbox
+// containment (SandboxFileSystem) is honoured even in this mode.
+func PythonStyle(root http.FileSystem) http.Handler {
 	return &pythonStyleHandler{
 		root: root,
 	}