[client] Fix expression order in legacy nftables route rules (#7011)

client/firewall/nftables/legacy_rule_linux_test.go

@@ -0,0 +1,60 @@
+package nftables
+
+import (
+	"testing"
+
+	"github.com/google/nftables/expr"
+	"github.com/stretchr/testify/require"
+)
+
+func TestBuildLegacyRouteRuleExpressions(t *testing.T) {
+	sourcePayload := &expr.Payload{}
+	sourceCmp := &expr.Cmp{}
+	destinationPayload := &expr.Payload{}
+	destinationCmp := &expr.Cmp{}
+	nilSourceDestination := &expr.Payload{}
+	nilDestinationSource := &expr.Cmp{}
+
+	tests := []struct {
+		name        string
+		source      []expr.Any
+		destination []expr.Any
+		matches     []expr.Any
+	}{
+		{
+			name:        "both non-empty",
+			source:      []expr.Any{sourcePayload, sourceCmp},
+			destination: []expr.Any{destinationPayload, destinationCmp},
+			matches:     []expr.Any{sourcePayload, sourceCmp, destinationPayload, destinationCmp},
+		},
+		{
+			name:        "nil source",
+			destination: []expr.Any{nilSourceDestination},
+			matches:     []expr.Any{nilSourceDestination},
+		},
+		{
+			name:    "nil destination",
+			source:  []expr.Any{nilDestinationSource},
+			matches: []expr.Any{nilDestinationSource},
+		},
+		{
+			name: "both nil",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := buildLegacyRouteRuleExpressions(tt.source, tt.destination)
+
+			require.Len(t, got, len(tt.matches)+2)
+			for i, match := range tt.matches {
+				require.Same(t, match, got[i])
+			}
+
+			require.IsType(t, &expr.Counter{}, got[len(tt.matches)])
+			verdict, ok := got[len(tt.matches)+1].(*expr.Verdict)
+			require.True(t, ok)
+			require.Equal(t, expr.VerdictAccept, verdict.Kind)
+		})
+	}
+}

client/firewall/nftables/router_linux.go

@@ -953,6 +953,17 @@ func (r *router) addMSSClampingRules() error {
 	return r.conn.Flush()
 }
 
+func buildLegacyRouteRuleExpressions(sourceExp, destExp []expr.Any) []expr.Any {
+	exprs := make([]expr.Any, 0, len(sourceExp)+len(destExp)+2)
+	exprs = append(exprs, sourceExp...)
+	exprs = append(exprs, destExp...)
+	exprs = append(exprs,
+		&expr.Counter{},
+		&expr.Verdict{Kind: expr.VerdictAccept},
+	)
+	return exprs
+}
+
 // addLegacyRouteRule adds a legacy routing rule for mgmt servers pre route acls
 func (r *router) addLegacyRouteRule(pair firewall.RouterPair) error {
 	sourceExp, err := r.applyNetwork(pair.Source, nil, true)
@@ -965,15 +976,7 @@ func (r *router) addLegacyRouteRule(pair firewall.RouterPair) error {
 		return fmt.Errorf("apply destination: %w", err)
 	}
 
-	exprs := []expr.Any{
-		&expr.Counter{},
-		&expr.Verdict{
-			Kind: expr.VerdictAccept,
-		},
-	}
-
-	exprs = append(exprs, sourceExp...)
-	exprs = append(exprs, destExp...)
+	exprs := buildLegacyRouteRuleExpressions(sourceExp, destExp)
 
 	ruleKey := firewall.GenKey(firewall.ForwardingFormat, pair)