fix(policydsl): guard against deeply nested policies

common/policydsl/policyparser.go

@@ -26,6 +26,11 @@ const (
 	GateOutOf = "OutOf"
 )
 
+const (
+	maxPolicyStringLength = 100000
+	maxPolicyNestingDepth = 1024
+)
+
 // Role values for principals
 const (
 	RoleAdmin   = "admin"
@@ -233,6 +238,29 @@ func newContext() *context {
 	return &context{IDNum: 0, principals: make([]*mb.MSPPrincipal, 0)}
 }
 
+func validatePolicyString(policy string) error {
+	if len(policy) > maxPolicyStringLength {
+		return fmt.Errorf("policy string exceeds maximum length of %d characters", maxPolicyStringLength)
+	}
+
+	depth := 0
+	for _, r := range policy {
+		switch r {
+		case '(':
+			depth++
+			if depth > maxPolicyNestingDepth {
+				return fmt.Errorf("policy string exceeds maximum nesting depth of %d", maxPolicyNestingDepth)
+			}
+		case ')':
+			if depth > 0 {
+				depth--
+			}
+		}
+	}
+
+	return nil
+}
+
 // FromString takes a string representation of the policy,
 // parses it and returns a SignaturePolicyEnvelope that
 // implements that policy. The supported language is as follows:
@@ -252,6 +280,10 @@ func newContext() *context {
 //   - ROLE takes the value of any of the RoleXXX constants representing
 //     the required role
 func FromString(policy string) (*cb.SignaturePolicyEnvelope, error) {
+	if err := validatePolicyString(policy); err != nil {
+		return nil, err
+	}
+
 	// first we translate the and/or business into outof gates
 	intermediate, err := govaluate.NewEvaluableExpressionWithFunctions(
 		policy, map[string]govaluate.ExpressionFunction{

common/policydsl/policyparser_test.go

@@ -7,6 +7,8 @@ SPDX-License-Identifier: Apache-2.0
 package policydsl
 
 import (
+	"fmt"
+	"strings"
 	"testing"
 
 	"github.com/hyperledger/fabric-protos-go-apiv2/common"
@@ -406,3 +408,21 @@ func TestSecondPassBoundaryCheck(t *testing.T) {
 	require.Nil(t, p3)
 	require.EqualError(t, err3, "invalid t-out-of-n predicate, t 4, n 2")
 }
+
+func TestPolicyStringGuardrails(t *testing.T) {
+	t.Run("rejects excessive nesting", func(t *testing.T) {
+		policy := strings.Repeat("OR(", maxPolicyNestingDepth+1) + "'A.member'" + strings.Repeat(")", maxPolicyNestingDepth+1)
+
+		p, err := FromString(policy)
+		require.Nil(t, p)
+		require.EqualError(t, err, fmt.Sprintf("policy string exceeds maximum nesting depth of %d", maxPolicyNestingDepth))
+	})
+
+	t.Run("rejects oversized policy strings", func(t *testing.T) {
+		policy := "OR('A.member', '" + strings.Repeat("B", maxPolicyStringLength) + ".member')"
+
+		p, err := FromString(policy)
+		require.Nil(t, p)
+		require.EqualError(t, err, fmt.Sprintf("policy string exceeds maximum length of %d characters", maxPolicyStringLength))
+	})
+}