feat(saver): test sauce file is not escaping destination

pkg/recipe/saver.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"strings"
 
 	"gopkg.in/yaml.v3"
 )
@@ -13,6 +14,24 @@ const (
 	yamlIndent      int         = 2
 )
 
+func IsSafePath(basePath, filePath string) error {
+	absBasePath, err := filepath.Abs(basePath)
+	if err != nil {
+		return fmt.Errorf("invalid base path %q: %v", basePath, err)
+	}
+
+	absFilePath, err := filepath.Abs(filePath)
+	if err != nil {
+		return fmt.Errorf("invalid file path %q: %v", basePath, err)
+	}
+
+	if !strings.HasPrefix(absFilePath, absBasePath) {
+		return fmt.Errorf("file path escapes destination: %q outside %q", absFilePath, absBasePath)
+	}
+
+	return nil
+}
+
 // Save saves recipe to given destination
 func (re *Recipe) Save(dest string) error {
 	err := os.MkdirAll(dest, defaultFileMode)
@@ -197,8 +216,13 @@ func saveFileMap(files map[string]File, dest string) error {
 	for path, file := range files {
 		destPath := filepath.Join(dest, path)
 
+		err := IsSafePath(dest, destPath)
+		if err != nil {
+			return err
+		}
+
 		// Create file's parent directories (if not already exist)
-		err := os.MkdirAll(filepath.Dir(destPath), 0700)
+		err = os.MkdirAll(filepath.Dir(destPath), 0700)
 		if err != nil {
 			return err
 		}

pkg/recipe/saver_test.go

@@ -3,6 +3,7 @@ package recipe
 import (
 	"os"
 	"path/filepath"
+	"strings"
 	"testing"
 
 	"github.com/futurice/jalapeno/pkg/engine"
@@ -117,3 +118,37 @@ func TestSaveSauce(t *testing.T) {
 		}
 	}
 }
+
+func TestSaveSauceDoesNotWriteOutsideDest(t *testing.T) {
+	dir, err := os.MkdirTemp("", "jalapeno-test-saver")
+	if err != nil {
+		t.Fatalf("cannot create temp dir: %s", err)
+	}
+	defer os.RemoveAll(dir)
+
+	re := NewRecipe()
+	re.Name = "Test"
+	re.Version = "v0.0.1"
+	re.Templates = map[string]File{
+		"../foo.md": NewFile([]byte("foo")),
+	}
+
+	err = re.Validate()
+	if err != nil {
+		t.Fatalf("test recipe was not valid: %s", err)
+	}
+
+	sauce, err := re.Execute(engine.New(), nil, uuid.Must(uuid.NewV4()))
+	if err != nil {
+		t.Fatalf("recipe execution failed: %s", err)
+	}
+
+	err = sauce.Save(dir)
+	if err == nil {
+		t.Fatalf("should not have saved sauce")
+	}
+
+	if !strings.Contains(err.Error(), "file path escapes destination") {
+		t.Fatalf("error received was not expected: %s", err)
+	}
+}