fix(expression): add validation for empty expression list in CEL (#545)

* fix(expression): add validation for empty ExpressionOrList

Signed-off-by: Jason Cameron <git@jasoncameron.dev>

* fix(imports): block empty file imports with improved error checking logic

Signed-off-by: Jason Cameron <git@jasoncameron.dev>

* docs(expression): improve validation to error on empty CEL expressions

Signed-off-by: Jason Cameron <git@jasoncameron.dev>

---------

Signed-off-by: Jason Cameron <git@jasoncameron.dev>

docs/docs/CHANGELOG.md

@@ -29,6 +29,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Added Qualys SSL Labs whitelist policy
 - Fixed cookie deletion logic ([#520](https://github.com/TecharoHQ/anubis/issues/520), [#522](https://github.com/TecharoHQ/anubis/pull/522))
 - Add `--target-sni` flag/envvar to allow changing the value of the TLS handshake hostname in requests forwarded to the target service.
+- Fixed CEL expression matching validator to now properly error out when it receives empty expressions 
 
 ## v1.18.0: Varis zos Galvus
 

lib/policy/config/config.go

@@ -224,7 +224,7 @@ func (is *ImportStatement) open() (fs.File, error) {
 func (is *ImportStatement) load() error {
 	fin, err := is.open()
 	if err != nil {
-		return fmt.Errorf("can't open %s: %w", is.Import, err)
+		return fmt.Errorf("%w: %s: %w", ErrInvalidImportStatement, is.Import, err)
 	}
 	defer fin.Close()
 

lib/policy/config/expressionorlist.go

@@ -54,6 +54,9 @@ func (eol *ExpressionOrList) UnmarshalJSON(data []byte) error {
 }
 
 func (eol *ExpressionOrList) Valid() error {
+	if eol.Expression == "" && len(eol.All) == 0 && len(eol.Any) == 0 {
+		return ErrExpressionEmpty
+	}
 	if len(eol.All) != 0 && len(eol.Any) != 0 {
 		return ErrExpressionCantHaveBoth
 	}

lib/policy/config/expressionorlist_test.go

@@ -51,6 +51,13 @@ func TestExpressionOrListUnmarshal(t *testing.T) {
 			}`,
 			validErr: ErrExpressionCantHaveBoth,
 		},
+		{
+			name: "expression-empty",
+			inp: `{
+			"any": []
+			}`,
+			validErr: ErrExpressionEmpty,
+		},
 	} {
 		t.Run(tt.name, func(t *testing.T) {
 			var eol ExpressionOrList