fix: preserve rule order in diff and insert replacements in place

2026-10-03 20:52:01 +10:00
parent e16d95fb63
commit df7ebb8efe
3 changed files with 159 additions and 52 deletions
@@ -1,9 +1,11 @@
 package nftables

 import (
+	"reflect"
 	"testing"

 	"github.com/google/nftables/expr"
+	"golang.org/x/sys/unix"

 	"git.unkin.net/unkin/tomswall/internal/config"
 )
@@ -1553,6 +1555,8 @@ func diffTestConfig(port string) *config.Config {
 		Rules: []config.Rule{
 			{Action: config.RuleAccept, Source: "net:192.0.2.0/24", Dest: "fw", Proto: "tcp", DPort: config.PortSpec{port}},
 			{Action: config.RuleDNAT, Source: "net", Dest: "loc:198.51.100.10:80", Proto: "tcp", DPort: config.PortSpec{"8000"}},
+			{Action: config.RuleNFQueue, Source: "net", Dest: "fw", Proto: "tcp", DPort: config.PortSpec{"80"}, NFQueue: 3},
+			{Action: config.RuleRedirect, Source: "loc", Dest: "fw:192.0.2.1:3128", Proto: "tcp", DPort: config.PortSpec{"80"}},
 		},
 		SNAT:       []config.SNATRule{{Action: config.SNATAddress, Source: "198.51.100.0/24", Dest: "eth0", Address: "203.0.113.7"}},
 		PortGroups: make(map[string]config.PortGroup),
@@ -1580,3 +1584,106 @@ func TestDiffEngine_IndependentCompilesMatch(t *testing.T) {
 		t.Errorf("expected rule:0 replaced, got:\n%s", cs.Summary())
 	}
 }
+
+// shapes observed by applying diffTestConfig in a netns and reading it back
+func TestCompile_QueueRedirMatchKernelReadback(t *testing.T) {
+	state, err := NewCompiler(diffTestConfig("22")).Compile()
+	if err != nil {
+		t.Fatal(err)
+	}
+	want := map[string]expr.Any{
+		"rule:2": &expr.Queue{Num: 3, Total: 1},
+		"rule:3": &expr.Redir{RegisterProtoMin: 1, RegisterProtoMax: 1, Flags: unix.NF_NAT_RANGE_PROTO_SPECIFIED},
+	}
+	for _, rules := range state.Rules {
+		for _, r := range rules {
+			w, ok := want[r.Tag]
+			if !ok {
+				continue
+			}
+			if got := r.Exprs[len(r.Exprs)-1]; !reflect.DeepEqual(got, w) {
+				t.Errorf("%s: got %#v, want %#v", r.Tag, got, w)
+			}
+			delete(want, r.Tag)
+		}
+	}
+	for tag := range want {
+		t.Errorf("%s not compiled", tag)
+	}
+}
+
+func withHandles(s *FirewallState) *FirewallState {
+	h := uint64(100)
+	for _, rules := range s.Rules {
+		for i := range rules {
+			rules[i].Handle = h
+			h++
+		}
+	}
+	return s
+}
+
+func tags(rules []ManagedRule) []string {
+	out := make([]string, len(rules))
+	for i, r := range rules {
+		out[i] = r.Chain + "/" + r.Tag
+	}
+	return out
+}
+
+func TestDiffEngine_FreshApplyKeepsDesiredOrder(t *testing.T) {
+	desired, err := NewCompiler(diffTestConfig("22")).Compile()
+	if err != nil {
+		t.Fatal(err)
+	}
+	var want []string
+	for _, chain := range []string{"forward", "input", "output", "postrouting", "prerouting"} {
+		want = append(want, tags(desired.Rules[chain])...)
+	}
+	for i := 0; i < 20; i++ {
+		cs := computeDiff(&FirewallState{Rules: map[string][]ManagedRule{}}, desired)
+		if got := tags(cs.Add); !reflect.DeepEqual(got, want) {
+			t.Fatalf("add order:\n got %v\nwant %v", got, want)
+		}
+		for _, r := range cs.Add {
+			if r.Before != 0 {
+				t.Fatalf("fresh apply should append, %s has Before=%d", r.Tag, r.Before)
+			}
+		}
+	}
+}
+
+func TestDiffEngine_MiddleChangeInsertsBeforeNextRule(t *testing.T) {
+	current := withHandles(mustCompile(t, diffTestConfig("22")))
+	desired := mustCompile(t, diffTestConfig("2222"))
+
+	cs := computeDiff(current, desired)
+	if len(cs.Add) != 1 || len(cs.Remove) != 1 {
+		t.Fatalf("expected one replace, got:\n%s", cs.Summary())
+	}
+	input := current.Rules["input"]
+	idx := -1
+	for i, r := range input {
+		if r.Tag == "rule:0" {
+			idx = i
+		}
+	}
+	if idx < 1 || idx == len(input)-1 {
+		t.Fatalf("rule:0 at %d is not mid-chain", idx)
+	}
+	if cs.Remove[0].Handle != input[idx].Handle {
+		t.Errorf("removed handle %d, want %d", cs.Remove[0].Handle, input[idx].Handle)
+	}
+	if cs.Add[0].Before != input[idx+1].Handle {
+		t.Errorf("insert before %d, want %d (%s)", cs.Add[0].Before, input[idx+1].Handle, input[idx+1].Tag)
+	}
+}
+
+func mustCompile(t *testing.T, cfg *config.Config) *FirewallState {
+	t.Helper()
+	s, err := NewCompiler(cfg).Compile()
+	if err != nil {
+		t.Fatal(err)
+	}
+	return s
+}
@@ -3,6 +3,7 @@ package nftables
 import (
 	"fmt"
 	"reflect"
+	"sort"
 	"strings"

 	"github.com/google/nftables/expr"
@@ -13,6 +14,8 @@ type ManagedRule struct {
 	Handle uint64
 	Exprs  []expr.Any
 	Tag    string
+	// Before is the handle of the existing rule an added rule is inserted ahead of; 0 appends.
+	Before uint64
 }

 type FirewallState struct {
@@ -33,7 +36,11 @@ func (cs *ChangeSet) Summary() string {
 	if len(cs.Add) > 0 {
 		fmt.Fprintf(&b, "  + %d rule(s) to add\n", len(cs.Add))
 		for _, r := range cs.Add {
-			fmt.Fprintf(&b, "    + [%s] %s\n", r.Chain, r.Tag)
+			if r.Before != 0 {
+				fmt.Fprintf(&b, "    + [%s] %s (before handle %d)\n", r.Chain, r.Tag, r.Before)
+			} else {
+				fmt.Fprintf(&b, "    + [%s] %s\n", r.Chain, r.Tag)
+			}
 		}
 	}
 	if len(cs.Remove) > 0 {
@@ -45,69 +52,56 @@ func (cs *ChangeSet) Summary() string {
 	return b.String()
 }

+// Rules are first-match, so order matters: keep the common prefix and suffix of
+// each chain, replace the middle, and insert the new rules before the first kept
+// suffix rule (or append when there is none).
 func computeDiff(current, desired *FirewallState) *ChangeSet {
 	cs := &ChangeSet{}

-	currentByTag := make(map[string][]ManagedRule)
-	for _, rules := range current.Rules {
-		for _, r := range rules {
+	chains := make([]string, 0, len(current.Rules)+len(desired.Rules))
+	for c := range current.Rules {
+		chains = append(chains, c)
+	}
+	for c := range desired.Rules {
+		if _, ok := current.Rules[c]; !ok {
+			chains = append(chains, c)
+		}
+	}
+	sort.Strings(chains)
+
+	for _, chain := range chains {
+		var cur []ManagedRule
+		for _, r := range current.Rules[chain] {
 			if r.Tag != "" {
-				currentByTag[ruleKey(r)] = append(currentByTag[ruleKey(r)], r)
+				cur = append(cur, r)
 			}
 		}
-	}
+		want := desired.Rules[chain]

-	desiredByTag := make(map[string][]ManagedRule)
-	for _, rules := range desired.Rules {
-		for _, r := range rules {
-			desiredByTag[ruleKey(r)] = append(desiredByTag[ruleKey(r)], r)
+		pre := 0
+		for pre < len(cur) && pre < len(want) && ruleEqual(cur[pre], want[pre]) {
+			pre++
+		}
+		suf := 0
+		for suf < len(cur)-pre && suf < len(want)-pre &&
+			ruleEqual(cur[len(cur)-1-suf], want[len(want)-1-suf]) {
+			suf++
 		}
-	}

-	for tag, desiredRules := range desiredByTag {
-		currentRules, exists := currentByTag[tag]
-		if !exists {
-			cs.Add = append(cs.Add, desiredRules...)
-			continue
+		var before uint64
+		if suf > 0 {
+			before = cur[len(cur)-suf].Handle
 		}
-		if !rulesMatch(currentRules, desiredRules) {
-			cs.Remove = append(cs.Remove, currentRules...)
-			cs.Add = append(cs.Add, desiredRules...)
-		}
-	}
-
-	for tag, currentRules := range currentByTag {
-		if _, exists := desiredByTag[tag]; !exists {
-			cs.Remove = append(cs.Remove, currentRules...)
+		cs.Remove = append(cs.Remove, cur[pre:len(cur)-suf]...)
+		for _, r := range want[pre : len(want)-suf] {
+			r.Before = before
+			cs.Add = append(cs.Add, r)
 		}
 	}

 	return cs
 }

-// a tag can span chains and map iteration order is random, so group per chain
-func ruleKey(r ManagedRule) string {
-	return r.Chain + "\x00" + r.Tag
-}
-
-func rulesMatch(a, b []ManagedRule) bool {
-	if len(a) != len(b) {
-		return false
-	}
-	for i := range a {
-		if a[i].Chain != b[i].Chain {
-			return false
-		}
-		if !exprsEqual(a[i].Exprs, b[i].Exprs) {
-			return false
-		}
-	}
-	return true
-}
-
-func exprsEqual(a, b []expr.Any) bool {
-	if len(a) != len(b) {
-		return false
-	}
-	return reflect.DeepEqual(a, b)
+func ruleEqual(a, b ManagedRule) bool {
+	return a.Chain == b.Chain && a.Tag == b.Tag && reflect.DeepEqual(a.Exprs, b.Exprs)
 }
@@ -109,12 +109,18 @@ func (e *Engine) Apply(changes *ChangeSet) error {
 		if !ok {
 			return fmt.Errorf("unknown chain %q", r.Chain)
 		}
-		e.conn.AddRule(&nftables.Rule{
+		rule := &nftables.Rule{
 			Table:    table,
 			Chain:    chain,
 			Exprs:    r.Exprs,
 			UserData: []byte(r.Tag),
-		})
+		}
+		if r.Before != 0 {
+			rule.Position = r.Before
+			e.conn.InsertRule(rule)
+		} else {
+			e.conn.AddRule(rule)
+		}
 	}

 	return e.conn.Flush()