Fix/issue #21 path traversal vulnerability

internal/handler/handler.go

@@ -16,16 +16,25 @@ type Handler struct {
 }
 
 func copyFilesToTmpDir(tmpDir string, files map[string]string) error {
-	for f, src := range files {
-		in := filepath.Join(tmpDir, f)
-		if strings.Contains(f, "/") {
-			if err := os.MkdirAll(filepath.Dir(in), 0755); err != nil {
-				return err
-			}
+	cleanTmpDir, err := filepath.Abs(tmpDir)
+	if err != nil {
+		return err
+	}
+
+	for relPath, content := range files {
+		targetPath := filepath.Join(cleanTmpDir, relPath)
+
+		rel, err := filepath.Rel(cleanTmpDir, targetPath)
+		if err != nil || strings.HasPrefix(rel, "..") {
+			return fmt.Errorf("invalid file path %q: path traversal detected", relPath)
 		}
-		//nolint
-		if err := os.WriteFile(in, []byte(src), 0644); err != nil {
-			return fmt.Errorf("error creating temp file %q: %w", in, err)
+
+		if err = os.MkdirAll(filepath.Dir(targetPath), 0755); err != nil {
+			return err
+		}
+
+		if err = os.WriteFile(targetPath, []byte(content), 0644); err != nil {
+			return fmt.Errorf("error creating temp file %q: %w", targetPath, err)
 		}
 	}
 

internal/handler/handler_test.go

@@ -0,0 +1,79 @@
+package handler
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func TestCopyFilesToTmpDir_PathTraversal_ShouldBeBlocked(t *testing.T) {
+	testCases := []struct {
+		name     string
+		filename string
+	}{
+		{"dot-dot-slash", "../escape.txt"},
+		{"multiple-dot-dot", "../../escape.txt"},
+		{"deeply-nested-escape", "subdir/../../escape.txt"},
+		{"dot-dot-in-middle", "foo/../../../escape.txt"},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			subTmpDir, err := os.MkdirTemp("", "test_sub_sandbox")
+			if err != nil {
+				t.Fatalf("failed to create temp dir: %v", err)
+			}
+			defer os.RemoveAll(subTmpDir)
+
+			files := map[string]string{
+				tc.filename: "escaped content",
+			}
+
+			err = copyFilesToTmpDir(subTmpDir, files)
+
+			if err == nil {
+				t.Errorf("expected error for path traversal attempt %q, got nil", tc.filename)
+			} else if !strings.Contains(err.Error(), "path traversal detected") {
+				t.Errorf("expected 'path traversal detected' error, got: %v", err)
+			}
+
+			resultPath := filepath.Join(subTmpDir, tc.filename)
+			cleanPath := filepath.Clean(resultPath)
+			if _, statErr := os.Stat(cleanPath); statErr == nil {
+				t.Errorf("file should NOT exist at escaped path: %s", cleanPath)
+			}
+		})
+	}
+}
+
+func TestCopyFilesToTmpDir_ValidPaths(t *testing.T) {
+	tmpDir, err := os.MkdirTemp("", "test_sandbox")
+	if err != nil {
+		t.Fatalf("failed to create temp dir: %v", err)
+	}
+	defer os.RemoveAll(tmpDir)
+
+	validFiles := map[string]string{
+		"main.go":           "package main",
+		"src/util.go":       "package src",
+		"src/lib/helper.go": "package lib",
+	}
+
+	err = copyFilesToTmpDir(tmpDir, validFiles)
+	if err != nil {
+		t.Fatalf("copyFilesToTmpDir failed for valid paths: %v", err)
+	}
+
+	for filename, expectedContent := range validFiles {
+		filePath := filepath.Join(tmpDir, filename)
+		content, err := os.ReadFile(filePath)
+		if err != nil {
+			t.Errorf("failed to read %s: %v", filename, err)
+			continue
+		}
+		if string(content) != expectedContent {
+			t.Errorf("content mismatch for %s: got %q, want %q", filename, string(content), expectedContent)
+		}
+	}
+}