security/authorization: util function for converting CEL expression s…

…tring (#3822)

* security/authorization: add the util function to compile string cel expr

security/authorization/engine/engine.go

@@ -33,7 +33,7 @@ import (
 	"google.golang.org/protobuf/proto"
 )
 
-var logger = grpclog.Component("channelz")
+var logger = grpclog.Component("authorization")
 
 var stringAttributeMap = map[string]func(*AuthorizationArgs) (string, error){
 	"request.url_path":                    (*AuthorizationArgs).getRequestURLPath,

security/authorization/util/util.go

@@ -0,0 +1,63 @@
+/*
+ *
+ * Copyright 2020 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package engine
+
+import (
+	"errors"
+
+	expr "google.golang.org/genproto/googleapis/api/expr/v1alpha1"
+	"google.golang.org/protobuf/proto"
+
+	"github.com/google/cel-go/cel"
+	"github.com/google/cel-go/checker/decls"
+)
+
+func compileCel(env *cel.Env, expr string) (*cel.Ast, error) {
+	ast, iss := env.Parse(expr)
+	// Report syntactic errors, if present.
+	if iss.Err() != nil {
+		return nil, iss.Err()
+	}
+	// Type-check the expression for correctness.
+	checked, iss := env.Check(ast)
+	if iss.Err() != nil {
+		return nil, iss.Err()
+	}
+	// Check the result type is a Boolean.
+	if !proto.Equal(checked.ResultType(), decls.Bool) {
+		return nil, errors.New("failed to compile CEL string: get non-bool value")
+	}
+	return checked, nil
+}
+
+func compileStringToCheckedExpr(expr string, declarations []*expr.Decl) (*expr.CheckedExpr, error) {
+	env, err := cel.NewEnv(cel.Declarations(declarations...))
+	if err != nil {
+		return nil, err
+	}
+	checked, err := compileCel(env, expr)
+	if err != nil {
+		return nil, err
+	}
+	checkedExpr, err := cel.AstToCheckedExpr(checked)
+	if err != nil {
+		return nil, err
+	}
+	return checkedExpr, nil
+}

security/authorization/util/util_test.go

@@ -0,0 +1,121 @@
+/*
+ *
+ * Copyright 2020 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package engine
+
+import (
+	"testing"
+
+	expr "google.golang.org/genproto/googleapis/api/expr/v1alpha1"
+	"google.golang.org/grpc/internal/grpctest"
+
+	"github.com/google/cel-go/cel"
+	"github.com/google/cel-go/checker/decls"
+)
+
+type s struct {
+	grpctest.Tester
+}
+
+func Test(t *testing.T) {
+	grpctest.RunSubTests(t, s{})
+}
+
+func (s) TestStringConvert(t *testing.T) {
+	declarations := []*expr.Decl{
+		decls.NewIdent("request.url_path", decls.String, nil),
+		decls.NewIdent("request.host", decls.String, nil),
+		decls.NewIdent("connection.uri_san_peer_certificate", decls.String, nil),
+	}
+	env, err := cel.NewEnv()
+	if err != nil {
+		t.Fatalf("Failed to create the CEL environment")
+	}
+	for _, test := range []struct {
+		desc             string
+		wantEvalOutcome  bool
+		wantParsingError bool
+		wantEvalError    bool
+		expr             string
+		authzArgs        map[string]interface{}
+	}{
+		{
+			desc:            "single primitive match",
+			wantEvalOutcome: true,
+			expr:            "request.url_path.startsWith('/pkg.service/test')",
+			authzArgs:       map[string]interface{}{"request.url_path": "/pkg.service/test"},
+		},
+		{
+			desc:            "single compare match",
+			wantEvalOutcome: true,
+			expr:            "connection.uri_san_peer_certificate == 'cluster/ns/default/sa/admin'",
+			authzArgs:       map[string]interface{}{"connection.uri_san_peer_certificate": "cluster/ns/default/sa/admin"},
+		},
+		{
+			desc:            "single primitive no match",
+			wantEvalOutcome: false,
+			expr:            "request.url_path.startsWith('/pkg.service/test')",
+			authzArgs:       map[string]interface{}{"request.url_path": "/source/pkg.service/test"},
+		},
+		{
+			desc:            "primitive and compare match",
+			wantEvalOutcome: true,
+			expr:            "request.url_path == '/pkg.service/test' && connection.uri_san_peer_certificate == 'cluster/ns/default/sa/admin'",
+			authzArgs: map[string]interface{}{"request.url_path": "/pkg.service/test",
+				"connection.uri_san_peer_certificate": "cluster/ns/default/sa/admin"},
+		},
+		{
+			desc:             "parse error field not present in environment",
+			wantParsingError: true,
+			expr:             "request.source_path.startsWith('/pkg.service/test')",
+			authzArgs:        map[string]interface{}{"request.url_path": "/pkg.service/test"},
+		},
+		{
+			desc:          "eval error argument not included in environment",
+			wantEvalError: true,
+			expr:          "request.url_path.startsWith('/pkg.service/test')",
+			authzArgs:     map[string]interface{}{"request.source_path": "/pkg.service/test"},
+		},
+	} {
+		test := test
+		t.Run(test.desc, func(t *testing.T) {
+			checked, err := compileStringToCheckedExpr(test.expr, declarations)
+			if (err != nil) != test.wantParsingError {
+				t.Fatalf("Error mismatch in conversion, wantParsingError =%v, got %v", test.wantParsingError, err != nil)
+			}
+			if test.wantParsingError {
+				return
+			}
+			ast := cel.CheckedExprToAst(checked)
+			program, err := env.Program(ast)
+			if err != nil {
+				t.Fatalf("Failed to create CEL Program: %v", err)
+			}
+			eval, _, err := program.Eval(test.authzArgs)
+			if (err != nil) != test.wantEvalError {
+				t.Fatalf("Error mismatch in evaluation, wantEvalError =%v, got %v", test.wantEvalError, err != nil)
+			}
+			if test.wantEvalError {
+				return
+			}
+			if eval.Value() != test.wantEvalOutcome {
+				t.Fatalf("Error in evaluating converted CheckedExpr: want %v, got %v", test.wantEvalOutcome, eval.Value())
+			}
+		})
+	}
+}