smallwebwaf/internal/servewaf/refusallimit_test.go

package servewaf_test

import (
	"maps"
	"net/http"
	"net/netip"
	"reflect"
	"testing"
	"time"

	"sneak.berlin/go/smallwebwaf/internal/alerts"
	"sneak.berlin/go/smallwebwaf/internal/bans"
	"sneak.berlin/go/smallwebwaf/internal/ratelimit"
	"sneak.berlin/go/smallwebwaf/internal/requestlog"
	"sneak.berlin/go/smallwebwaf/internal/servewaf"
)

const errorBurstThreshold = "SWWAF_ERROR_BURST_THRESHOLD"

// refused is a request the tests here send, which servewaf refuses after a rule
// file match.
type refused int

const (
	// blockRule is a request testRules' block rule refuses with 403.
	blockRule refused = iota
	// banRule is one its ban rule refuses with 403, and bans the client
	// for.
	banRule
)

// send sends r from the client at from, checks its answer and log line as
// sender.request does, and returns the line.
func (r refused) send(s *sender, from string) logLine {
	s.t.Helper()

	switch r {
	case blockRule:
		return s.request(from, blockedPath, http.StatusForbidden,
			requestlog.ActionRuleBlocked)
	case banRule:
		return s.request(from, probePath, http.StatusForbidden, requestlog.ActionBanned)
	}

	s.t.Fatalf("no request for the refusal %d", r)

	return logLine{}
}

// startForErrorBurst is startWithClock with testRules, the metrics token and
// SWWAF_ERROR_BURST_THRESHOLD at threshold, and the settings in env.
func startForErrorBurst(
	t *testing.T, threshold string, env map[string]string,
) (*sender, *clock, *servewaf.Server) {
	t.Helper()

	settings := map[string]string{
		errorBurstThreshold: threshold,
		rulesDir:            writeRules(t, testRules),
		metricsToken:        token,
	}
	maps.Copy(settings, env)

	return startWithClock(t, "", settings)
}

func TestErrorBurstBreaksAtOneOverTheThreshold(t *testing.T) {
	t.Parallel()

	for _, tc := range []struct {
		name string
		// refusals are four, one over the threshold of three.
		refusals []refused
	}{
		{"block rule", []refused{blockRule, blockRule, blockRule, blockRule}},
		{"a ban rule last", []refused{blockRule, blockRule, blockRule, banRule}},
	} {
		t.Run(tc.name, func(t *testing.T) {
			t.Parallel()

			s, _, _ := startForErrorBurst(t, "3", nil)

			// Three refusals break nothing, and the app's answers between
			// them are not counted.
			for i, r := range tc.refusals[:3] {
				line := r.send(s, client)
				if line.LimitHit != "" || line.Offence != "" {
					t.Errorf("refusal %d: log line has limit_hit %q and offence %q, "+
						"want none", i+1, line.LimitHit, line.Offence)
				}

				s.get(client, http.StatusOK, requestlog.ActionForward)
			}

			// The fourth is answered as the others were, breaks the error
			// burst, and bans the client.
			line := tc.refusals[3].send(s, client)
			if line.LimitHit != requestlog.LimitHitErrorBurst ||
				line.Offence != requestlog.OffenceLimit {
				t.Errorf("log line has limit_hit %q and offence %q, want error_burst "+
					"and limit", line.LimitHit, line.Offence)
			}

			s.get(client, http.StatusForbidden, requestlog.ActionBanned)
		})
	}
}

func TestRefusalLimitBanNamesItsHeuristicWindowCountAndLimit(t *testing.T) {
	t.Parallel()

	s, _, _ := startForErrorBurst(t, "1", nil)

	const ruleFigures = `{"rule_id": "blocked", "rule_action": "block"}`

	line := blockRule.send(s, client)
	wantHeuristic(t, line, "rule_files", ruleFigures)
	wantAfterAnswerHeuristic(t, line, "", "null")

	// The second refusal is the request refusal_limit bans for, and the line
	// names both.
	line = blockRule.send(s, client)
	wantHeuristic(t, line, "rule_files", ruleFigures)
	wantAfterAnswerHeuristic(t, line, "refusal_limit",
		`{"window": "minute", "count": 2, "limit": 1}`)
}

func TestErrorBurstBanNotesHistoryAndMetrics(t *testing.T) {
	t.Parallel()

	s, clk, server := startForErrorBurst(t, "2", nil)
	start := clk.Now()

	blockRule.send(s, client)
	blockRule.send(s, client)
	line := blockRule.send(s, client)

	expires := start.Add(time.Hour)
	if line.BanExpires != requestlog.FormatTime(expires) {
		t.Errorf("log line has ban_expires %q, want an hour on", line.BanExpires)
	}

	netblock := netip.MustParsePrefix(client + "/32")
	want := bans.Ban{
		Netblock: netblock,
		Start:    start,
		Expires:  expires,
		Cause:    bans.CauseLimit,
		Reason:   "refusals per minute over the limit of 2",
		Notes: bans.Notes{
			Kind:   ratelimit.KindRefusals,
			Limit:  2,
			Window: minute,
			Count:  3,
			Request: bans.Request{
				Time:      start,
				Method:    http.MethodGet,
				Host:      appHost,
				Path:      blockedPath,
				Status:    http.StatusForbidden,
				UserAgent: userAgent,
			},
			Requests: 3,
		},
	}

	got := server.Ledger.Bans(netblock)
	if len(got) != 1 || !reflect.DeepEqual(got[0], want) {
		t.Fatalf("bans\n%+v\nwant\n%+v", got, want)
	}

	wantOffences := ratelimit.Offences{Limit: 1, RuleBlocked: 3}
	if offences := historyOf(t, server, client).Offences; offences != wantOffences {
		t.Errorf("history counts the offences %+v, want %+v", offences, wantOffences)
	}

	metrics := s.scrape()
	wantMetric(t, metrics, `smallwebwaf_rate_limit_hits_total{instance="app",`+
		`kind="refusals",window="minute"}`, 1)
	wantMetric(t, metrics, `smallwebwaf_offences_total{instance="app",kind="limit"}`, 1)
	wantMetric(t, metrics,
		`smallwebwaf_offences_total{instance="app",kind="rule_blocked"}`, 3)
	wantMetric(t, metrics, `smallwebwaf_bans_made_total{cause="limit",instance="app"}`, 1)
}

func TestErrorBurstIsNotLoweredForAClientWithLowerLimits(t *testing.T) {
	t.Parallel()

	geojsURL, _ := startGeoJS(t)
	s, _, server := startWithClock(t, geojsURL, map[string]string{
		lookupTimeout:       "1h",
		errorBurstThreshold: "2",
		rulesDir:            writeRules(t, testRules),
		countryLimitPercent: countryDEHalf,
	})

	// Half of the threshold would be one, which the second refusal is over.
	for range 2 {
		line := blockRule.send(s, fromDE)
		if line.LimitHit != "" {
			t.Errorf("log line has limit_hit %q, want none", line.LimitHit)
		}
	}

	blockRule.send(s, fromDE)

	got := server.Ledger.Bans(netip.MustParsePrefix(fromDE + "/32"))
	if len(got) != 1 || got[0].Notes.Limit != 2 || got[0].Notes.LimitPercent != nil {
		t.Errorf("bans %+v, want one for the limit of 2, without a limit percentage", got)
	}
}

func TestErrorBurstDoesNotCountTheAppsAnswers(t *testing.T) {
	t.Parallel()

	statuses := map[string]int{
		"/missing":   http.StatusNotFound,
		"/private":   http.StatusUnauthorized,
		"/forbidden": http.StatusForbidden,
	}
	s, _, _, queue := startAppWithAlerts(t, func(w http.ResponseWriter, r *http.Request) {
		w.WriteHeader(statuses[r.URL.Path])
	}, map[string]string{errorBurstThreshold: "1", rulesDir: writeRules(t, testRules)})

	for range 2 {
		for path, status := range statuses {
			s.request(client, path, status, requestlog.ActionForward)
		}
	}

	// The first refusal is one, not over the threshold.
	line := blockRule.send(s, client)
	if line.LimitHit != "" {
		t.Errorf("log line has limit_hit %q, want none", line.LimitHit)
	}

	// No ban was made, nor its alert raised.
	s.request(client, "/missing", http.StatusNotFound, requestlog.ActionForward)
	wantAlerts(t, queue)
}

func TestErrorBurstOffOrAtItsDefault(t *testing.T) {
	t.Parallel()

	for _, tc := range []struct {
		threshold string
		// broken is whether the 31st refusal breaks the error burst.
		broken bool
	}{
		{"", true},
		{off, false},
	} {
		t.Run(errorBurstThreshold+"="+tc.threshold, func(t *testing.T) {
			t.Parallel()

			env := map[string]string{rulesDir: writeRules(t, testRules)}
			if tc.threshold != "" {
				env[errorBurstThreshold] = tc.threshold
			}

			s, _, _ := startWithClock(t, "", env)

			var line logLine
			for range 31 {
				line = blockRule.send(s, client)
			}

			if broken := line.LimitHit == requestlog.LimitHitErrorBurst; broken != tc.broken {
				t.Errorf("the 31st refusal broke the error burst: %t, want %t",
					broken, tc.broken)
			}
		})
	}
}

func TestErrorBurstCountsEachClientTheChecksApplyTo(t *testing.T) {
	t.Parallel()

	const (
		allowed = "192.0.2.60" // in SWWAF_ALLOW_NETS
		exempt  = "192.0.2.50" // in SWWAF_RATE_LIMIT_EXEMPT_NETS
	)

	s, _, _ := startForErrorBurst(t, "1", map[string]string{
		allowNets: allowed, rateLimitExemptNets: exempt,
	})

	// A client in SWWAF_ALLOW_NETS is not refused, and so not counted.
	for range 3 {
		s.request(allowed, blockedPath, http.StatusOK, requestlog.ActionForward)
	}

	// One the rate limits do not apply to is.
	blockRule.send(s, exempt)

	line := blockRule.send(s, exempt)
	if line.LimitHit != requestlog.LimitHitErrorBurst {
		t.Errorf("log line has limit_hit %q, want error_burst", line.LimitHit)
	}

	s.get(exempt, http.StatusForbidden, requestlog.ActionBanned)
}

func TestErrorBurstBanSetsTheRefusalsBackToZero(t *testing.T) {
	t.Parallel()

	s, clk, _ := startForErrorBurst(t, "1", map[string]string{limitBanDuration: "1s"})

	blockRule.send(s, client)
	blockRule.send(s, client)

	// Within the same minute, once the ban has ended, the next refusal is
	// the first again.
	clk.advance(time.Second)

	line := blockRule.send(s, client)
	if line.LimitHit != "" {
		t.Errorf("log line has limit_hit %q, want none", line.LimitHit)
	}
}

func TestObserveModeLogsAndAlertsTheErrorBurst(t *testing.T) {
	t.Parallel()

	s, clk, server, queue := startWithAlerts(t, map[string]string{
		mode:                observe,
		errorBurstThreshold: "1",
		rulesDir:            writeRules(t, testRules),
	})
	start := clk.Now()
	held := bans.Ban{
		Netblock: netip.MustParsePrefix(otherClient + "/32"),
		Start:    start,
		Expires:  start.Add(time.Hour),
		Cause:    bans.CauseAdmin,
	}
	server.Ledger.Load([]bans.Ban{held})

	// Under a ban, enforce mode would have refused these before the rule, so
	// they are not counted.
	for range 2 {
		line := s.request(otherClient, blockedPath, http.StatusOK,
			requestlog.ActionForward)
		wantWouldAction(t, line, requestlog.ActionBanned)

		if line.LimitHit != "" {
			t.Errorf("log line has limit_hit %q, want none", line.LimitHit)
		}
	}

	// The block rule's refusal, which enforce mode would have answered 403,
	// is the second of the client's, and would have banned it.
	s.request(client, blockedPath, http.StatusOK, requestlog.ActionForward)

	line := s.request(client, blockedPath, http.StatusOK, requestlog.ActionForward)
	wantWouldAction(t, line, requestlog.ActionRuleBlocked)

	if line.LimitHit != requestlog.LimitHitErrorBurst || line.BanExpires != "" {
		t.Errorf("log line has limit_hit %q and ban_expires %q, want error_burst "+
			"and none", line.LimitHit, line.BanExpires)
	}

	if got := server.Ledger.Snapshot(); len(got) != 1 || !reflect.DeepEqual(got[0], held) {
		t.Errorf("bans %+v, want only the one held", got)
	}

	waiting := queue.Snapshot().Waiting[alerts.DestinationWebhook]
	if len(waiting) != 1 {
		t.Fatalf("%d alerts wait, want 1: %+v", len(waiting), waiting)
	}

	notes, _ := waiting[0].Detail["notes"].(bans.Notes)
	if notes.Kind != ratelimit.KindRefusals || notes.Count != 2 ||
		notes.Request.Status != http.StatusForbidden {
		t.Errorf("the alert's notes are %+v, want two refusals, the last answered 403",
			notes)
	}

	alert := banAlert(alerts.EventBan, start, client, bans.Ban{
		Netblock: netip.MustParsePrefix(client + "/32"), Cause: bans.CauseLimit,
		Reason: "refusals per minute over the limit of 1", Notes: notes,
	}, requestlog.FormatTime(start.Add(time.Hour)))
	alert.Detail["mode"] = observe
	wantAlerts(t, queue, alert)
}