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/proxy/bans.go

@@ -6,6 +6,7 @@ import (
 
 	"sneak.berlin/go/smallwebwaf/internal/bans"
 	"sneak.berlin/go/smallwebwaf/internal/requestlog"
+	"sneak.berlin/go/smallwebwaf/internal/rules"
 )
 
 // banResponse is a refusal answered with SWWAF_BAN_RESPONSE, and logged
@@ -51,20 +52,12 @@ func (rq *request) limitBroken(now time.Time) bool {
 
 	netblock := rq.netblock()
 	ban := rq.h.ledger.BanForLimit(netblock, now, bans.Notes{
-		Country: rq.line.Country,
-		Limit:   hit.Limit,
-		Window:  hit.Window,
-		Count:   hit.Requests,
-		Request: bans.Request{
-			Time:      now,
-			Method:    rq.in.Method,
-			Host:      rq.in.Host,
-			Path:      rq.in.URL.RequestURI(),
-			Status:    rq.h.config.BanResponse,
-			UserAgent: rq.in.UserAgent(),
-		},
-		// The histories count this request only once it has ended.
-		Requests: rq.h.limiter.Requests(netblock) + 1,
+		Country:  rq.line.Country,
+		Limit:    hit.Limit,
+		Window:   hit.Window,
+		Count:    hit.Requests,
+		Request:  rq.noted(now),
+		Requests: rq.netblockRequests(netblock),
 	})
 	rq.h.limiter.Reset(group)
 	rq.line.BanExpires = banExpires(ban)
@@ -72,6 +65,40 @@ func (rq *request) limitBroken(now time.Time) bool {
 	return true
 }
 
+// banForAttack bans the client's netblock at now for a clear sign of
+// attack, the match of rule, a ban rule.
+func (rq *request) banForAttack(now time.Time, rule rules.Rule) {
+	netblock := rq.netblock()
+	ban := rq.h.ledger.BanForAttack(netblock, now, bans.Notes{
+		Country:  rq.line.Country,
+		RuleID:   rule.ID,
+		Target:   rule.Target,
+		Request:  rq.noted(now),
+		Requests: rq.netblockRequests(netblock),
+	})
+	rq.line.BanExpires = banExpires(ban)
+}
+
+// noted is the request, refused at now with SWWAF_BAN_RESPONSE, as the
+// notes of the ban it makes keep it.
+func (rq *request) noted(now time.Time) bans.Request {
+	return bans.Request{
+		Time:      now,
+		Method:    rq.in.Method,
+		Host:      rq.in.Host,
+		Path:      rq.in.URL.RequestURI(),
+		Status:    rq.h.config.BanResponse,
+		UserAgent: rq.in.UserAgent(),
+	}
+}
+
+// netblockRequests is how many requests netblock has sent since it was
+// first seen, this one included: the histories count it only once it has
+// ended.
+func (rq *request) netblockRequests(netblock netip.Prefix) int64 {
+	return rq.h.limiter.Requests(netblock) + 1
+}
+
 // netblock is the netblock a ban on the client covers: its IPv4 address,
 // widened to SWWAF_BAN_SCOPE_V4_PREFIX, or the IPv6 group clientGroup
 // counts it in.