Trap paths, and the error burst banning a client refused too often (closes #115)

SWWAF_TRAP_PATHS: a request whose path, as a path rule sees it, is one
of them is a clear sign of attack, banned as a ban rule's match is; the
ban's notes give its trap_path. Checked after the rate limits, before the
rule files.

SWWAF_ERROR_BURST_THRESHOLD (default 30, or off): more refusals in a
minute after a block or ban rule or a trap path, or for a missing or
wrong token, ban the client as a broken limit does. Counted in
clients.json's minute_refusals; limit_hit error_burst, notes kind
refusals.

A token refusal is now the offence token_refused, and
smallwebwaf_offences_total counts every kind the history does.

Judgement call: the threshold is not lowered by a client's limit percentage.

Model: opus-5-5

internal/proxy/trappaths_test.go

@@ -0,0 +1,115 @@
+package proxy_test
+
+import (
+	"net/http"
+	"net/netip"
+	"reflect"
+	"testing"
+	"time"
+
+	"sneak.berlin/go/smallwebwaf/internal/bans"
+	"sneak.berlin/go/smallwebwaf/internal/requestlog"
+)
+
+// trapPaths is the setting's name, and trapPathList what the tests set it
+// to.
+const (
+	trapPaths    = "SWWAF_TRAP_PATHS"
+	trapPathList = "/wp-login.php,/xmlrpc.php"
+)
+
+func TestTrapPathBansAsABanRuleDoes(t *testing.T) {
+	t.Parallel()
+
+	const allowed = "192.0.2.60" // in SWWAF_ALLOW_NETS
+
+	// A block rule for the same path: the trap path comes first.
+	s, clk, server := startWithClock(t, "", map[string]string{
+		trapPaths:   trapPathList,
+		rulesDir:    writeRules(t, `wp  path  block  ^/wp-login\.php$`),
+		allowNets:   allowed,
+		banResponse: "429",
+	})
+	start := clk.Now()
+
+	// Only the path itself, as the client sent it, is a trap path.
+	for _, path := range []string{
+		"/wp-login.php/", "/WP-LOGIN.PHP", "/blog/xmlrpc.php", "/%77p-login.php",
+	} {
+		s.request(otherClient, path, http.StatusOK, requestlog.ActionForward)
+	}
+
+	// A client in SWWAF_ALLOW_NETS is not checked.
+	s.request(allowed, "/xmlrpc.php", http.StatusOK, requestlog.ActionForward)
+
+	// The query is not part of the path.
+	line := s.request(client, "/wp-login.php?redirect_to=x", http.StatusTooManyRequests,
+		requestlog.ActionBanned)
+	wantRuleIDs(t, line)
+
+	if line.BanExpires != requestlog.FormatTime(start.Add(7*24*time.Hour)) {
+		t.Errorf("log line has ban_expires %q, want seven days on", line.BanExpires)
+	}
+
+	netblock := netip.MustParsePrefix(client + "/32")
+	want := bans.Ban{
+		Netblock: netblock,
+		Start:    start,
+		Expires:  start.Add(7 * 24 * time.Hour),
+		Cause:    bans.CauseAttack,
+		Reason:   "asked for the trap path /wp-login.php",
+		Notes: bans.Notes{
+			TrapPath: "/wp-login.php",
+			Request: bans.Request{
+				Time:      start,
+				Method:    http.MethodGet,
+				Host:      appHost,
+				Path:      "/wp-login.php?redirect_to=x",
+				Status:    http.StatusTooManyRequests,
+				UserAgent: userAgent,
+			},
+			Requests: 1,
+		},
+	}
+
+	got := server.Ledger.Bans(netblock)
+	if len(got) != 1 || !reflect.DeepEqual(got[0], want) {
+		t.Fatalf("bans\n%+v\nwant\n%+v", got, want)
+	}
+
+	// The next request is refused under the ban, and makes it permanent.
+	line = s.get(client, http.StatusTooManyRequests, requestlog.ActionBanned)
+	if line.BanExpires != permanent {
+		t.Errorf("log line has ban_expires %q, want permanent", line.BanExpires)
+	}
+}
+
+func TestTrapPathsNeedNoRuleFiles(t *testing.T) {
+	t.Parallel()
+
+	s, _, _ := startWithClock(t, "", map[string]string{
+		trapPaths:             trapPathList,
+		"SWWAF_RULES_ENABLED": "false",
+	})
+
+	s.request(client, "/xmlrpc.php", http.StatusForbidden, requestlog.ActionBanned)
+}
+
+func TestObserveModeLogsWhatATrapPathWouldDo(t *testing.T) {
+	t.Parallel()
+
+	s, _, server := startWithClock(t, "", map[string]string{
+		trapPaths: trapPathList,
+		mode:      observe,
+	})
+
+	line := s.request(client, "/xmlrpc.php", http.StatusOK, requestlog.ActionForward)
+	wantWouldAction(t, line, requestlog.ActionBanned)
+
+	// No ban was made.
+	s.get(client, http.StatusOK, requestlog.ActionForward)
+
+	if got := server.Ledger.Snapshot(); len(got) != 0 {
+		t.Errorf("bans %+v, want none", got)
+	}
+}