Rule files, and bans for a clear sign of attack (closes #24)

Every *.rules file in SWWAF_RULES_DIR is read at start and on each
change, and each request is checked against the rules after the rate
limits: log notes a match, block refuses with 403, ban refuses and bans
the netblock for SWWAF_ATTACK_BAN_DURATION, made permanent by its next
request or clear sign of attack. path, query and uri are matched as the
request line sent them. bans.json gains each ban's cause, and ban notes
count earlier bans by cause. The image ships 00-default.rules.

Judgement call: a header sent twice is matched with its values joined
by ", ".
Judgement call: SWWAF_MAX_BAN_DURATION does not cap a ban for an attack.
Not in this unit: offences for rule matches, with the error burst.

Model: opus-5-5

internal/metrics/metrics.go

@@ -14,6 +14,7 @@ import (
 	"sneak.berlin/go/smallwebwaf/internal/bans"
 	"sneak.berlin/go/smallwebwaf/internal/ratelimit"
 	"sneak.berlin/go/smallwebwaf/internal/requestlog"
+	"sneak.berlin/go/smallwebwaf/internal/rules"
 )
 
 // Metrics are smallwebwaf's metrics. They are safe for concurrent use.
@@ -30,7 +31,9 @@ type Metrics struct {
 	rateLimitHits        *prometheus.CounterVec
 	sizeAndTimeLimitHits *prometheus.CounterVec
 	offences             *prometheus.CounterVec
-	countries            *countries
+	// ruleMatches are made by AddRules.
+	ruleMatches *prometheus.CounterVec
+	countries   *countries
 
 	// GeoJSRequests are the requests to GeoJS, and GeoJSFailures those
 	// that failed. GeoJSUnanswered are the requests whose client counted
@@ -135,19 +138,22 @@ func New(topN int) *Metrics {
 
 // AddBansAndClients adds the metrics read from the ledger and the table
 // of clients as the metrics are asked for: the bans made since the start,
-// the bans active and permanent at now, and the clients in the table.
+// by cause, the bans active and permanent at now, and the clients in the
+// table.
 func (m *Metrics) AddBansAndClients(
 	ledger *bans.Ledger, limiter *ratelimit.Limiter, now func() time.Time,
 ) {
-	m.registry.MustRegister(
-		// Every ban smallwebwaf makes so far is for a broken limit.
-		prometheus.NewCounterFunc(prometheus.CounterOpts{
+	for _, cause := range []string{bans.CauseLimit, bans.CauseAttack} {
+		m.registry.MustRegister(prometheus.NewCounterFunc(prometheus.CounterOpts{
 			Name:        "smallwebwaf_bans_made_total",
 			Help:        "Bans made, by cause.",
-			ConstLabels: prometheus.Labels{"cause": "limit"},
+			ConstLabels: prometheus.Labels{"cause": cause},
 		}, func() float64 {
-			return float64(ledger.Made())
-		}),
+			return float64(ledger.Made(cause))
+		}))
+	}
+
+	m.registry.MustRegister(
 		prometheus.NewGaugeFunc(prometheus.GaugeOpts{
 			Name: "smallwebwaf_active_bans",
 			Help: "Bans active now, the permanent ones included.",
@@ -173,6 +179,24 @@ func (m *Metrics) AddBansAndClients(
 	)
 }
 
+// AddRules adds the metrics of the rule files: the requests that matched
+// each rule, which RuleMatched counts, and the rules loaded from
+// ruleFiles, read as the metrics are asked for. It is called once, before
+// RuleMatched.
+func (m *Metrics) AddRules(ruleFiles *rules.Files) {
+	m.ruleMatches = counterVec("smallwebwaf_rule_matches_total",
+		"Requests that matched a rule of the rule files, by its id and action.",
+		[]string{"rule_id", "action"})
+
+	m.registry.MustRegister(m.ruleMatches,
+		prometheus.NewGaugeFunc(prometheus.GaugeOpts{
+			Name: "smallwebwaf_rules_loaded",
+			Help: "Rules loaded from the rule files.",
+		}, func() float64 {
+			return float64(ruleFiles.Len())
+		}))
+}
+
 // ServeHTTP answers with the metrics in the Prometheus text format.
 func (m *Metrics) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	m.handler.ServeHTTP(w, r)
@@ -219,6 +243,12 @@ func (m *Metrics) RequestEnded(
 	}
 }
 
+// RuleMatched counts a request that matched the rule id, whose action is
+// action.
+func (m *Metrics) RuleMatched(id, action string) {
+	m.ruleMatches.WithLabelValues(id, action).Inc()
+}
+
 // StateFileWritten counts a write of the state file name, of size bytes,
 // that ended with err.
 func (m *Metrics) StateFileWritten(name string, size int, err error) {