ghupdate: add checksum verification and extraction path containment guard

internal/ghupdate/ghupdate_test.go

@@ -1,6 +1,9 @@
 package ghupdate
 
 import (
+	"archive/tar"
+	"compress/gzip"
+	"os"
 	"path/filepath"
 	"testing"
 )
@@ -43,3 +46,59 @@ func TestExtractFailure(t *testing.T) {
 		t.Fatal("Expected Extract to fail due to missing tar.gz file")
 	}
 }
+
+func TestArchivePath(t *testing.T) {
+	destDir := t.TempDir()
+	for _, name := range []string{
+		"",
+		"..",
+		filepath.Join("..", "file"),
+		filepath.Join("dir", "..", "..", "file"),
+		string(os.PathSeparator) + filepath.Join("tmp", "file"),
+	} {
+		if _, err := archivePath(destDir, name); err == nil {
+			t.Errorf("expected %q to be rejected", name)
+		}
+	}
+
+	name := filepath.Join("dir", "file")
+	if path, err := archivePath(destDir, name); err != nil || path != filepath.Join(destDir, name) {
+		t.Errorf("archivePath(%q) = %q, %v", name, path, err)
+	}
+}
+
+func TestExtractTarGzRejectsPathTraversal(t *testing.T) {
+	testDir := t.TempDir()
+	archivePath := filepath.Join(testDir, "malicious.tar.gz")
+	destDir := filepath.Join(testDir, "extract")
+	escapedPath := filepath.Join(testDir, "escaped")
+
+	archive, err := os.Create(archivePath)
+	if err != nil {
+		t.Fatal(err)
+	}
+	gz := gzip.NewWriter(archive)
+	tw := tar.NewWriter(gz)
+	if err := tw.WriteHeader(&tar.Header{Name: "../escaped", Mode: 0600, Size: 1}); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := tw.Write([]byte("x")); err != nil {
+		t.Fatal(err)
+	}
+	if err := tw.Close(); err != nil {
+		t.Fatal(err)
+	}
+	if err := gz.Close(); err != nil {
+		t.Fatal(err)
+	}
+	if err := archive.Close(); err != nil {
+		t.Fatal(err)
+	}
+
+	if err := extract(archivePath, destDir); err == nil {
+		t.Fatal("expected path traversal archive to be rejected")
+	}
+	if _, err := os.Stat(escapedPath); !os.IsNotExist(err) {
+		t.Fatalf("path traversal wrote %s", escapedPath)
+	}
+}