waf: refuse request lines and header lines over 8 KiB first (closes #339)

The header limits now also refuse a request line over 8 KiB with 414
(action request_line_too_long) and a header line over 8 KiB, Host
included, with 431. Like the other header limits they are fixed, run
first and make no ban. One long query string or cookie no longer keeps
the Core Rule Set busy for a third of a second.

Model: opus-5-5

README.md

@@ -260,7 +260,7 @@ Every setting the code reads, with its default:
 | `SWW_WAF_LOOKUP_SOURCE`                           | `geojs`                                                                                  | Where each client's AS number and country come from: `geojs` (a web service), `file` (a local database) or `off`.                                                                                                                                               |
 | `SWW_WAF_LOOKUP_DB_PATH`                          | empty                                                                                    | The IPinfo Lite database file, in its `.mmdb` form, read while the source is `file`.                                                                                                                                                                            |
 | `SWW_WAF_ASN_AND_COUNTRY_LOOKUP_TIMEOUT_MS`       | `800`                                                                                    | How long a request waits for its client's first GeoJS answer when a setting needs it, and how long a request to GeoJS may take, in milliseconds.                                                                                                                |
-| `SWW_WAF_ADD_LOOKUP_HEADERS`                      | `false`                                                                                  | `true` passes the app the client's AS number and country in `X-Client-ASN` and `X-Client-Country`.                                                                                                                                                              |
+| `SWW_WAF_ADD_LOOKUP_HEADERS`                      | `true`, or `false` while the lookup source is `off`                                      | `true` passes the app the client's AS number and country in `X-Client-ASN` and `X-Client-Country`.                                                                                                                                                              |
 | `SWW_WAF_EXCLUSIVELY_ALLOWED_COUNTRIES`           | empty                                                                                    | When set, the only countries whose clients get through; a client the lookup cannot place is refused too.                                                                                                                                                        |
 | `SWW_WAF_TAG_LISTS`                               | empty                                                                                    | Address lists that each add a tag to their clients' requests, as `name=URL` pairs, such as `torexit=https://example.com/tor.txt`.                                                                                                                               |
 | `SWW_WAF_TAG_DENY`                                | empty                                                                                    | Tags whose requests are refused, such as `torexit,country=CN`.                                                                                                                                                                                                  |
@@ -540,9 +540,10 @@ request reaches the app.
 A refused visitor is answered with `SWW_WAF_BAN_RESPONSE`. A `block` rule or a
 Core Rule Set match answers `403` and bans nobody, since the Core Rule Set has
 false positives; such refusals count toward `SWW_WAF_REFUSALS_LIMIT_PER_MINUTE`
-instead. A request over the header limits of step 3 is answered `431`, and bans
+instead. A request over the header limits of step 3 is answered `414` for a
-nobody either. `rproxy` itself answers `405` to a method it does not pass on,
+request line over 8 KiB and `431` otherwise. It bans nobody either. `rproxy`
-and the status for a size or time limit, such as `413` for a body too large.
+itself answers `405` to a method it does not pass on, and the status for a size
+or time limit, such as `413` for a body too large.
 
 ### Clients and bans
 

SPEC.md

@@ -151,26 +151,26 @@ field gives that name. `refusal_limit` and `byte_limits` give theirs in
       around its address, a /64 by default, since one abuser usually controls a
       whole /64. A client is therefore one IPv4 address or one IPv6 group.
 3. The header limits (`header_limits`; see "Answering in time"). They come first
-   after `SWW_WAF_ALLOW_NETS`, since they only count header fields and cookies.
+   after `SWW_WAF_ALLOW_NETS`, since they only measure lines and count header
-   Next, the tag lists (`tag_lists`; see "Request tags"). Each list that holds
+   fields and cookies. Next, the tag lists (`tag_lists`; see "Request tags").
-   the client adds its tag. Next, `routewatch_tags` adds the client's `asn=` and
+   Each list that holds the client adds its tag. Next, `routewatch_tags` adds
-   `prefix=` tags while `SWW_WAF_ROUTEWATCH_URL` is set. A client in
+   the client's `asn=` and `prefix=` tags while `SWW_WAF_ROUTEWATCH_URL` is set.
-   `SWW_WAF_ALLOW_NETS` skips the header limits and gets no tag.
+   A client in `SWW_WAF_ALLOW_NETS` skips the header limits and gets no tag.
 4. The static lists. A client in `SWW_WAF_ALLOW_NETS` skips steps 5 to 15, the
    byte limits and the refusal limit. A client in `SWW_WAF_DENY_NETS` is refused
    (`deny_nets`); a client in both lists is let through.
 5. Bans. A client under a ban is refused (`active_ban`; see "Bans").
 6. The lookup, unless `SWW_WAF_LOOKUP_SOURCE` is `off` (see "Lookup of AS number
-   and country"). The request goes on at once. It waits for the first GeoJS
+   and country"). The request waits for the first GeoJS answer, up to
-   answer, up to `SWW_WAF_ASN_AND_COUNTRY_LOOKUP_TIMEOUT_MS`, only when one of
+   `SWW_WAF_ASN_AND_COUNTRY_LOOKUP_TIMEOUT_MS`, when one of these needs it:
-   these needs it:
+    - `SWW_WAF_ADD_LOOKUP_HEADERS`, which is `true` by default;
     - the country list;
     - a biased threshold;
     - `SWW_WAF_TAG_DENY` or `SWW_WAF_TAG_LIMIT_PERCENT` naming an `asn=` or
-      `country=` tag;
+      `country=` tag.
-    - `SWW_WAF_ADD_LOOKUP_HEADERS`.
 
-    A request that ends before the answer comes is logged without it.
+    Otherwise the request goes on at once. A request that ends before the answer
+    comes is logged without it.
 
 7. The country list (`countries`; see "Country list").
 8. The reputation sources (see "Reputation"), in this order:
@@ -197,10 +197,10 @@ field gives that name. `refusal_limit` and `byte_limits` give theirs in
 16. A path under `/_sww/` is answered `404`, so that the app never sees that
     prefix.
 17. `rproxy` passes the request to `SWW_RPROXY_UPSTREAM_URL`, streaming (see
-    "Passing a request to the app"). With `SWW_WAF_ADD_LOOKUP_HEADERS`,
+    "Passing a request to the app"). While `SWW_WAF_ADD_LOOKUP_HEADERS` is
-    `X-Client-ASN` and `X-Client-Country` are added for the app's own logs; a
+    `true`, as by default, `X-Client-ASN` and `X-Client-Country` are added for
-    header whose value is unknown is left out. Whatever that setting says, any
+    the app's own logs; a header whose value is unknown is left out. Whatever
-    such header the client sent is removed.
+    that setting says, any such header the client sent is removed.
 18. After the visitor's answer has ended, `rproxy` sends the report (see "The
     report"). `waf` then counts:
     - For a request it allowed, the body bytes of the response, of the request
@@ -252,9 +252,9 @@ does not reach neighbours who did nothing. Requests refused under a ban are not
 counted against limits. They are counted in the client's history and in the
 ban's notes.
 
-A request over the header limits is refused with `431` before the bans are
+A request over the header limits is refused with `414` or `431` before the bans
-checked (see "Answering in time"). It makes no ban, makes no ban permanent and
+are checked (see "Answering in time"). It makes no ban, makes no ban permanent
-is not counted in a ban's notes.
+and is not counted in a ban's notes.
 
 An offence is a request `waf` holds against the client. It is one of:
 
@@ -2373,15 +2373,15 @@ runs no check, writes no request log line and counts nothing in the metrics.
 answer but the last below carries `X-Sww-Disposition`.
 
 - `X-Sww-Disposition: allow`, status `200`, no body. `rproxy` passes the request
-  to the app. With `SWW_WAF_ADD_LOOKUP_HEADERS` the answer also carries
+  to the app. While `SWW_WAF_ADD_LOOKUP_HEADERS` is `true`, the answer also
-  `X-Client-ASN` and `X-Client-Country`, which `rproxy` adds to the request it
+  carries `X-Client-ASN` and `X-Client-Country`, which `rproxy` adds to the
-  passes on. A header whose value is unknown is left out.
+  request it passes on. A header whose value is unknown is left out.
 - `X-Sww-Disposition: deny`, with the status, headers and body the visitor is to
   get. `rproxy` gives them to the visitor, less this header. The status is one
   of:
     - `SWW_WAF_BAN_RESPONSE`, for a refusal;
     - `403`, for a `block` rule or the Core Rule Set;
-    - `431`, for a request over the header limits;
+    - `414` or `431`, for a request over the header limits;
     - `404`, for a path under `/_sww/` that passes the checks, so that the app
       never sees that prefix.
 - `X-Sww-Disposition: close`, status `200`, no body. This takes the place of a
@@ -2442,22 +2442,31 @@ never wait. These can still wait for GeoJS:
 - a rule file;
 - the Core Rule Set.
 
-The header limits are fixed, with no setting. `waf` refuses a request over
+The header limits are fixed, with no setting. A line's length is in bytes and
-either one:
+does not count its line ending. `waf` refuses a request whose request line is
+longer than 8 KiB with `414`. An example is `GET /search?q=` followed by 30,000
+characters.
 
+It refuses a request with `431` for any of:
+
+- a header line longer than 8 KiB. Each value of a header sent twice is a line
+  of its own. `Host` counts as a line.
 - more than 50 cookies. Each part of its `Cookie` headers between semicolons
   counts as one, unless it is empty or only spaces and tabs.
 - more than 100 header fields. A header sent twice counts twice. `Host` and
   `Transfer-Encoding` do not count. `X-Request-ID` and `X-Forwarded-Proto` do.
 
-Real clients never reach these limits. The answer is `deny` with `431`, and the
+Real clients rarely reach these limits. nginx refuses lines over 8 KiB by
-log line's action is `request_header_too_large`. The refusal makes no ban and is
+default, and Apache's default limit is about the same. The answer is `deny`. The
-no offence.
+log line's action is `request_line_too_long` for `414` and
+`request_header_too_large` for `431`. The refusal makes no ban and is no
+offence.
 
 The header limits are the first check after `SWW_WAF_ALLOW_NETS`. A request over
 them is refused before any later check runs. So it causes no lookup, no query to
 an outside source and no rule match, and the rate limits do not count it. A
-client under a ban or in `SWW_WAF_DENY_NETS` also gets `431` for such a request.
+client under a ban or in `SWW_WAF_DENY_NETS` also gets `414` or `431` for such a
+request.
 
 The limits apply on every path and in every `SWW_WAF_CORE_RULE_SET_MODE`. A
 client in `SWW_WAF_ALLOW_NETS` skips them, as it skips the Core Rule Set. In
@@ -2465,9 +2474,10 @@ client in `SWW_WAF_ALLOW_NETS` skips them, as it skips the Core Rule Set. In
 other check runs on it.
 
 The Core Rule Set runs each of its rules on each cookie, so thousands of small
-cookies would keep it busy for over a second. Within the limits, one long cookie
+cookies would keep it busy for over a second. One 30 KB cookie or query string
-or query string can still keep it busy for a fraction of a second. So enough
+would keep it busy for a third of a second or more. A request with several long
-such requests at once can overload `waf` past
+`Cookie` lines, each within the limits, can keep it as busy. Enough such
+requests at once can still overload `waf` past
 `SWW_RPROXY_WAF_BACKEND_TIMEOUT_MS`.
 
 ### The report

docs/request-log.md

@@ -102,7 +102,8 @@ Every one of these lines has:
       ban this request made or made permanent;
     - `country_denied`, `client_is_rate_limited`, `blocked_by_block_rule` and
       `blocked_by_core_rule_set`: refused by that check;
-    - `request_header_too_large`: over a header limit;
+    - `request_line_too_long`: a request line over the header limits;
+    - `request_header_too_large`: headers over the header limits;
     - `own_endpoint`: answered at one of `waf`'s own endpoints, or `404` for a
       path under `/_sww/`.
 - `would_action`: in `observe` mode, what `enforce` mode would have done with a
@@ -124,7 +125,10 @@ Every one of these lines has:
     - `rate_limits`: `window`, `count` and `limit`;
     - `trap_paths`: `path`, the trap path asked for;
     - `rule_files`: `rule_id` and `rule_action`, of the rule that refused it;
-    - `header_limits`: `fields`, `fields_limit`, `cookies` and `cookies_limit`;
+    - `header_limits`: for a request line, `request_line_bytes` and
+      `request_line_bytes_limit`; for headers, `longest_header_line_bytes`,
+      `header_line_bytes_limit`, `fields`, `fields_limit`, `cookies` and
+      `cookies_limit`;
     - `core_rule_set`: `score`, and `threshold`,
       `SWW_WAF_CORE_RULE_SET_SCORE_THRESHOLD`;
     - `refusal_limit`: `window`, `count` and `limit`, of the refusal limit;

docs/settings.md

@@ -150,7 +150,7 @@ cut off; the client is banned.
 - `SWW_WAF_LOOKUP_SOURCE` (default `geojs`): `geojs`, `file` or `off`. `off`
   stops the start while a setting that needs a lookup is set:
     - `SWW_WAF_EXCLUSIVELY_ALLOWED_COUNTRIES`;
-    - `SWW_WAF_ADD_LOOKUP_HEADERS`;
+    - `SWW_WAF_ADD_LOOKUP_HEADERS` set to `true`;
     - `SWW_WAF_TAG_DENY` or `SWW_WAF_TAG_LIMIT_PERCENT` naming a `country=` tag,
       or an `asn=` tag while `SWW_WAF_ROUTEWATCH_URL` is unset;
     - the two byte percentage lists and `SWW_WAF_ASN_LIMIT_PERCENT_URL`;
@@ -161,9 +161,11 @@ cut off; the client is banned.
 - `SWW_WAF_ASN_AND_COUNTRY_LOOKUP_TIMEOUT_MS` (default `800`): how long a
   request waits for its client's first answer from GeoJS, and how long a request
   to GeoJS may take. A time in milliseconds; never `off`.
-- `SWW_WAF_ADD_LOOKUP_HEADERS` (default `false`): `true` has `rproxy` pass the
+- `SWW_WAF_ADD_LOOKUP_HEADERS` (default `true`): `true` has `rproxy` pass the
   app the client's AS number in `X-Client-ASN` and its country in
-  `X-Client-Country`.
+  `X-Client-Country`. The default is `false` while `SWW_WAF_LOOKUP_SOURCE` is
+  `off`. With GeoJS, a new client's first request waits for its answer, up to
+  `SWW_WAF_ASN_AND_COUNTRY_LOOKUP_TIMEOUT_MS`.
 
 ## Country list
 
@@ -421,8 +423,9 @@ A few limits are fixed rather than settings:
 - at most 20,000 anomaly counters are kept;
 - each alert destination's queue holds at most 1,000 alerts;
 - `waf` holds at most 10,000 answered requests awaiting their reports;
-- `waf` refuses a request with more than 50 cookies or more than 100 header
+- `waf` refuses a request with a request line or header line over 8 KiB, more
-  fields (see "Answering in time" under "`waf`" in [`SPEC.md`](../SPEC.md));
+  than 50 cookies or more than 100 header fields (see "Answering in time" under
+  "`waf`" in [`SPEC.md`](../SPEC.md));
 - `rproxy` takes a request line and headers of at most 32 KiB, and closes a
   kept-open connection idle for 120 seconds;
 - `rproxy` reads at most 1 MiB of the body of `waf`'s answer, and answers `502`

internal/config/waf.go

@@ -84,7 +84,8 @@ type WAF struct {
 	// client's first answer from GeoJS while a setting needs it
 	// (SWW_WAF_ASN_AND_COUNTRY_LOOKUP_TIMEOUT_MS), which cannot be off.
 	// AddLookupHeaders is true when the app is passed the client's AS number
-	// and country in headers (SWW_WAF_ADD_LOOKUP_HEADERS).
+	// and country in headers (SWW_WAF_ADD_LOOKUP_HEADERS), by default unless
+	// LookupSource is off.
 	LookupSource               string
 	LookupDBPath               string
 	ASNAndCountryLookupTimeout time.Duration
@@ -549,7 +550,6 @@ func WAFFromEnvironment(v *viper.Viper) (*WAF, error) {
 			"SWW_WAF_ASN_AND_COUNTRY_LOOKUP_TIMEOUT_MS",
 			"800",
 		),
-		AddLookupHeaders: env.boolean("SWW_WAF_ADD_LOOKUP_HEADERS", "false"),
 		ExclusivelyAllowedCountries: env.countries(
 			"SWW_WAF_EXCLUSIVELY_ALLOWED_COUNTRIES", ""),
 		TagLists:        env.tagLists("SWW_WAF_TAG_LISTS"),
@@ -724,6 +724,9 @@ func WAFFromEnvironment(v *viper.Viper) (*WAF, error) {
 
 	cfg.LogRemoteAppName = env.appName("SWW_WAF_LOG_REMOTE_APP_NAME",
 		cfg.InstanceName, cfg.LogRemoteURL != nil)
+	// The app gets the headers by default, unless no client is looked up.
+	cfg.AddLookupHeaders = env.boolean("SWW_WAF_ADD_LOOKUP_HEADERS",
+		strconv.FormatBool(cfg.LookupSource != off))
 	cfg.BlocklistAction, cfg.BlocklistLimitPercent = env.action(
 		"SWW_WAF_BLOCKLIST_ACTION", "deny")
 	cfg.DNSBLAbuseIPDBAction, cfg.DNSBLAbuseIPDBLimitPercent = env.action(

internal/config/waf_test.go

@@ -287,6 +287,7 @@ func TestDefaults(t *testing.T) {
 	})
 	wantLookupSettings(t, cfg, config.WAF{
 		LookupSource: defaultLookupSource, ASNAndCountryLookupTimeout: 800 * time.Millisecond,
+		AddLookupHeaders: true,
 	})
 	wantByteLimitSettings(t, cfg, config.WAF{
 		BytesLimitPerMinute: 0, BytesLimitPerHour: 50 << 30,
@@ -1395,13 +1396,13 @@ func TestLookupSettingsAsSet(t *testing.T) {
 	t.Parallel()
 
 	cfg := wafFromEnvironment(t, environment{
-		asnAndCountryLookupTimeout: "500", addLookupHeaders: enabled,
+		asnAndCountryLookupTimeout: "500", addLookupHeaders: disabled,
 	})
 	wantLookupSettings(t, cfg, config.WAF{
 		LookupSource: defaultLookupSource, ASNAndCountryLookupTimeout: 500 * time.Millisecond,
-		AddLookupHeaders: true,
 	})
 
+	// With no client looked up, the headers are off unless set.
 	cfg = wafFromEnvironment(t, environment{lookupSource: off})
 	wantLookupSettings(t, cfg, config.WAF{
 		LookupSource: off, ASNAndCountryLookupTimeout: 800 * time.Millisecond,
@@ -1422,6 +1423,10 @@ func TestLookupDBPathGoesWithTheFileSourceAlone(t *testing.T) {
 			cfg.LookupSource, cfg.LookupDBPath, path)
 	}
 
+	if !cfg.AddLookupHeaders {
+		t.Error("headers off by default with lookups from file, want on")
+	}
+
 	for _, tc := range []struct {
 		env  environment
 		want string
@@ -2927,7 +2932,7 @@ func TestLogsEachSettingWithItsValue(t *testing.T) {
 		lookupSource:                   defaultLookupSource,
 		lookupDBPath:                   "",
 		asnAndCountryLookupTimeout:     "800",
-		addLookupHeaders:               disabled,
+		addLookupHeaders:               enabled,
 		allowedCountries:               "",
 		tagLists:                       "",
 		tagDeny:                        "",

internal/requestlog/requestlog.go

@@ -21,7 +21,12 @@ const (
 	// the app.
 	ActionForward = "forward"
 
-	// ActionRequestHeaderTooLarge is a request over the header limits.
+	// ActionRequestLineTooLong is a request whose request line is too long for
+	// the header limits.
+	ActionRequestLineTooLong = "request_line_too_long"
+
+	// ActionRequestHeaderTooLarge is a request whose headers are over the
+	// header limits.
 	ActionRequestHeaderTooLarge = "request_header_too_large"
 
 	// ActionClientIsRateLimited is a request refused because it took its
@@ -143,7 +148,7 @@ type Line struct {
 	// taken with a request it would have refused: ActionClientDenied,
 	// ActionTemporarilyBanned, ActionPermanentlyBanned, ActionCountryDenied,
 	// ActionClientIsRateLimited, ActionBlockedByBlockRule,
-	// ActionBlockedByCoreRuleSet, or, in waf,
+	// ActionBlockedByCoreRuleSet, or, in waf, ActionRequestLineTooLong or
 	// ActionRequestHeaderTooLarge for the header limits.
 	WouldAction string `json:"would_action,omitempty"`
 	// Heuristic is the name of the heuristic that refused the request, in

internal/waf/anomaly_test.go

@@ -349,6 +349,7 @@ func TestRequestCountsForTheASNumberGeoJSGivesBeforeItEnds(t *testing.T) {
 		map[string]string{
 			trustedProxies:                 trustLocalhost,
 			asnAndCountryLookupTimeout:     "3600000",
+			addLookupHeaders:               falseValue,
 			anomalyASN + requestsPerMinute: aLot,
 		})
 	server.Store(started)

internal/waf/answertime_test.go

@@ -39,6 +39,7 @@ const (
 	// The header limits SPEC.md gives.
 	cookieLimit      = 50
 	headerFieldLimit = 100
+	lineLimit        = 8192
 	// cookieHeader is the header the cookie limit counts.
 	cookieHeader = "Cookie"
 	// tooLarge is how waf refuses a request over the header limits.
@@ -104,11 +105,139 @@ func TestHeaderLimitRefusalNamesItsHeuristicCountsAndLimits(t *testing.T) {
 	fillHeaders(req, headerFieldLimit+1)
 	do(t, req)
 
+	// The longest header line is X-Request-ID's, with its 26-character id.
 	wantHeuristic(
 		t,
 		s.out.requestLine(t),
 		"header_limits",
-		`{"fields": 101, "fields_limit": 100, "cookies": 0, "cookies_limit": 50}`,
+		`{"longest_header_line_bytes": 40, "header_line_bytes_limit": 8192,
+		"fields": 101, "fields_limit": 100, "cookies": 0, "cookies_limit": 50}`,
+	)
+}
+
+// longQuery returns a path whose request line, sent by Go's client as
+// "GET <path> HTTP/1.1", is lineBytes long.
+func longQuery(lineBytes int) string {
+	const around = len("GET /?q= HTTP/1.1")
+
+	return "/?q=" + strings.Repeat("a", lineBytes-around)
+}
+
+func TestARequestLineOverTheLimitIsRefusedWith414BeforeAnyOtherCheck(
+	t *testing.T,
+) {
+	t.Parallel()
+
+	for _, tc := range []struct {
+		name      string
+		lineBytes int
+		// cookies is how many cookies the request carries.
+		cookies int
+		status  int
+		action  string
+	}{
+		{
+			"at the limit", lineLimit, 0, http.StatusOK,
+			requestlog.ActionForward,
+		},
+		{
+			"over the limit", lineLimit + 1, 0, http.StatusRequestURITooLong,
+			requestlog.ActionRequestLineTooLong,
+		},
+		{
+			"over the limit and the cookie limit", lineLimit + 1,
+			cookieLimit + 1, http.StatusRequestURITooLong,
+			requestlog.ActionRequestLineTooLong,
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			s := startWAF(t, "", map[string]string{coreRuleSetMode: block})
+			req := s.question(siteA, client, longQuery(tc.lineBytes))
+
+			if tc.cookies > 0 {
+				req.Header.Set(cookieHeader, cookies(tc.cookies))
+			}
+
+			got := do(t, req)
+			line := s.out.requestLine(t)
+
+			if tc.status == http.StatusOK {
+				wantDisposition(t, got, tc.status, waf.DispositionAllow)
+			} else {
+				wantDisposition(t, got, tc.status, waf.DispositionDeny)
+			}
+
+			wantLine(t, line, tc.status, tc.action)
+
+			refused := tc.status != http.StatusOK
+			if refused != (line.DurationCoreRuleSetMS == nil) {
+				t.Errorf(
+					"Core Rule Set time %v for a request refused: %t",
+					line.DurationCoreRuleSetMS,
+					refused,
+				)
+			}
+		})
+	}
+}
+
+func TestAHeaderLineOverTheLimitIsRefusedWith431(t *testing.T) {
+	t.Parallel()
+
+	for _, tc := range []struct {
+		name string
+		make func(*http.Request)
+		// refused is true for a request over the limit, and false for one at it.
+		refused bool
+	}{
+		{"a header line at the limit", func(req *http.Request) {
+			req.Header.Set("X-Long", strings.Repeat("a", lineLimit-len("X-Long: ")))
+		}, false},
+		{"a header line over the limit", func(req *http.Request) {
+			req.Header.Set("X-Long", strings.Repeat("a", lineLimit+1-len("X-Long: ")))
+		}, true},
+		{"one cookie over the limit", func(req *http.Request) {
+			req.Header.Set(cookieHeader, "a="+strings.Repeat("a", lineLimit))
+		}, true},
+		{"a Host line over the limit", func(req *http.Request) {
+			req.Host = strings.Repeat("a", lineLimit+1-len("Host: "))
+		}, true},
+		{"a header sent twice, each line within the limit", func(req *http.Request) {
+			req.Header.Add("X-Long", strings.Repeat("a", 8000))
+			req.Header.Add("X-Long", strings.Repeat("a", 8000))
+		}, false},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			s := startWAF(t, "", nil)
+			req := s.question(siteA, client, "/")
+			tc.make(req)
+
+			got := do(t, req)
+
+			if tc.refused {
+				wantDisposition(t, got, tooLarge, waf.DispositionDeny)
+			} else {
+				wantDisposition(t, got, http.StatusOK, waf.DispositionAllow)
+			}
+		})
+	}
+}
+
+func TestRequestLineRefusalNamesItsHeuristicLengthAndLimit(t *testing.T) {
+	t.Parallel()
+
+	s := startWAF(t, "", nil)
+	do(t, s.question(siteA, client, longQuery(lineLimit+1)))
+
+	wantHeuristic(
+		t,
+		s.out.requestLine(t),
+		"header_limits",
+		`{"request_line_bytes": 8193, "request_line_bytes_limit": 8192}`,
 	)
 }
 

internal/waf/biased_test.go

@@ -387,12 +387,14 @@ func TestRequestWaitsForItsLookupWhileABiasedThresholdIsSet(t *testing.T) {
 
 			// In a synctest bubble, as
 			// TestRequestWaitsAsLongAsTheASNAndCountryLookupTimeoutSays says,
-			// with a GeoJS that never answers.
+			// with a GeoJS that never answers. The headers, which need the
+			// answer too, are off.
 			synctest.Test(t, func(t *testing.T) {
 				server, out, _ := newWAF(t, silentGeoJSURL, time.Now,
 					map[string]string{
 						asnAndCountryLookupTimeout: strconv.FormatInt(
 							timeout.Milliseconds(), 10),
+						addLookupHeaders: falseValue,
 						tagLists:         "vpn=" + vpnList,
 						tc.setting:       tc.value,
 					})

internal/waf/countries_test.go

@@ -108,8 +108,11 @@ func TestCountryRefusalNamesItsHeuristicCountryAndSetting(t *testing.T) {
 	t.Parallel()
 
 	geojsURL, _ := startGeoJS(t)
+	// The headers are off, so that only the country list makes the request
+	// wait for its answer.
 	s, _, _ := startWithClock(t, geojsURL, map[string]string{
-		asnAndCountryLookupTimeout: "3600000", allowedCountries: "de",
+		asnAndCountryLookupTimeout: "3600000", addLookupHeaders: falseValue,
+		allowedCountries: "de",
 	})
 
 	line := s.get(
@@ -239,7 +242,10 @@ func TestPrivateAddressIsNeverLookedUp(t *testing.T) {
 		name string
 		env  map[string]string
 	}{
-		{"no setting needs the lookup", nil},
+		{
+			"no setting needs the lookup",
+			map[string]string{addLookupHeaders: falseValue},
+		},
 		{"a tag setting needs it", map[string]string{tagDeny: denyKP}},
 	} {
 		t.Run(tc.name, func(t *testing.T) {

internal/waf/headerlimits.go

@@ -10,16 +10,22 @@ import (
 	"sneak.berlin/go/smallwebwaf/internal/requestlog"
 )
 
-// The header limits: the most cookies and header fields a request may have.
+// The header limits: the most cookies and header fields a request may have,
-// Real clients never reach them.
+// and the longest its request line and each header line may be, in bytes, not
+// counting the line ending. Real clients rarely reach them. maxLineBytes is
+// what nginx allows by default.
 const (
 	maxCookies      = 50
 	maxHeaderFields = 100
+	maxLineBytes    = 8 << 10
 )
 
-// headerLimits refuses a request with more than maxHeaderFields header fields
+// headerLimits refuses a request with a request line longer than maxLineBytes,
-// or more than maxCookies cookies, with 431. Its figures are the request's
+// with 414. It refuses a request with a header line longer than maxLineBytes,
-// header fields and cookies, and the limit of each.
+// more than maxHeaderFields header fields or more than maxCookies cookies, with
+// 431. Its figures are the request line's length and its limit for 414. For
+// 431 they are the longest header line, the header fields and the cookies,
+// each with its limit.
 type headerLimits struct{}
 
 func (headerLimits) name() string { return "header_limits" }
@@ -29,20 +35,59 @@ func (headerLimits) check(
 	rq *request,
 	_ time.Time,
 ) *verdict {
+	requestLine := rq.requestLineBytes()
+	if requestLine > maxLineBytes {
+		return &verdict{
+			action: requestlog.ActionRequestLineTooLong,
+			figures: map[string]any{
+				"request_line_bytes":       requestLine,
+				"request_line_bytes_limit": maxLineBytes,
+			},
+		}
+	}
+
+	longest := rq.longestHeaderLineBytes()
 	fields, cookies := rq.headerCounts()
-	if fields <= maxHeaderFields && cookies <= maxCookies {
+
+	if longest <= maxLineBytes && fields <= maxHeaderFields &&
+		cookies <= maxCookies {
 		return nil
 	}
 
 	return &verdict{
 		action: requestlog.ActionRequestHeaderTooLarge,
 		figures: map[string]any{
+			"longest_header_line_bytes": longest,
+			"header_line_bytes_limit":   maxLineBytes,
 			"fields":                    fields, "fields_limit": maxHeaderFields,
 			"cookies": cookies, "cookies_limit": maxCookies,
 		},
 	}
 }
 
+// requestLineBytes returns the length of the request's request line, such as
+// "GET /search?q=x HTTP/1.1", not counting its line ending. The target is the
+// one the visitor sent, which rproxy's question carries unchanged.
+func (rq *request) requestLineBytes() int {
+	return len(rq.in.Method) + len(" ") + len(rq.in.RequestURI) +
+		len(" ") + len(rq.in.Proto)
+}
+
+// longestHeaderLineBytes returns the length of the request's longest header
+// line, such as "Cookie: a=1", not counting its line ending. Each value of a
+// header sent twice is a line of its own, and Host is a line too.
+func (rq *request) longestHeaderLineBytes() int {
+	longest := len("Host: ") + len(rq.in.Host)
+
+	for name, values := range rq.in.Header {
+		for _, value := range values {
+			longest = max(longest, len(name)+len(": ")+len(value))
+		}
+	}
+
+	return longest
+}
+
 // headerCounts returns the request's header fields, each value of a header sent
 // twice being one, and its cookies, each part of a Cookie header between
 // semicolons being one unless it is empty or only spaces and tabs. The Core

internal/waf/heuristics.go

@@ -41,8 +41,8 @@ const (
 
 // beforeLookup are the heuristics that run before the client's AS number and
 // country are looked up, so that a client they refuse is not looked up.
-// header_limits comes first: it only counts, and a request it refuses causes no
+// header_limits comes first: it only measures and counts, and a request it
-// other work.
+// refuses causes no other work.
 func beforeLookup() []heuristic {
 	return []heuristic{
 		headerLimits{},

internal/waf/lookup.go

@@ -12,7 +12,7 @@ import (
 )
 
 // The headers in which an answer of allow gives rproxy the client's AS number
-// and country, for the app, while SWW_WAF_ADD_LOOKUP_HEADERS is set. Go writes
+// and country, for the app, while SWW_WAF_ADD_LOOKUP_HEADERS is true. Go writes
 // every header name in this form, as it sends it and as it receives it, so
 // X-Client-ASN arrives as X-Client-Asn; header names are not case-sensitive.
 const (

internal/waf/lookup_test.go

@@ -36,6 +36,7 @@ func TestEveryClientIsLookedUpWithoutWaitingWhileNoSettingNeedsIt(
 	geojsURL, asked, release := startHeldGeoJS(t)
 	s, _, server := startWithClock(t, geojsURL, map[string]string{
 		asnAndCountryLookupTimeout: "3600000",
+		addLookupHeaders:           falseValue,
 		rateLimitPerMinute:         "1",
 	})
 
@@ -418,7 +419,7 @@ func TestClientsOwnLookupHeadersAreRemovedWhileTheSettingIsOff(
 		geojsURL,
 		time.Now,
 		map[string]string{
-			trustedProxies: trustLocalhost,
+			trustedProxies: trustLocalhost, addLookupHeaders: falseValue,
 		},
 	)
 	s := &sender{t: t, addr: addr, out: out}
@@ -457,6 +458,8 @@ func TestRequestWaitsAsLongAsTheASNAndCountryLookupTimeoutSays(
 			map[string]string{
 				asnAndCountryLookupTimeout: strconv.FormatInt(
 					timeout.Milliseconds(), 10),
+				// Off, so that only the country list makes the request wait.
+				addLookupHeaders: falseValue,
 				allowedCountries: "DE",
 			})
 

internal/waf/proxy_test.go

@@ -93,6 +93,10 @@ const off = "off"
 // on is the value that switches a setting that takes true or false on.
 const on = "true"
 
+// falseValue is the value that switches a setting that takes true or false
+// off.
+const falseValue = "false"
+
 // output collects what sww writes on stdout.
 type output struct {
 	mu  sync.Mutex

internal/waf/request.go

@@ -177,7 +177,7 @@ func requestHeaders(r *http.Request, names []string) map[string]string {
 // check is the one place where a request can be refused. It returns nil to let
 // the request through. The heuristics of checkClient decide: a request they
 // refuse is answered with SWW_WAF_BAN_RESPONSE, 403 for a block rule or the Core
-// Rule Set, or 431 for the header limits. In observe mode nothing is refused,
+// Rule Set, or 414 or 431 for the header limits. In observe mode nothing is refused,
 // and the log line names what enforce mode would have done. ctx is the
 // request's own context.
 func (rq *request) check(ctx context.Context) *refusal {
@@ -196,6 +196,8 @@ func (rq *request) check(ctx context.Context) *refusal {
 	case action == requestlog.ActionBlockedByBlockRule ||
 		action == requestlog.ActionBlockedByCoreRuleSet:
 		return &refusal{status: http.StatusForbidden, action: action}
+	case action == requestlog.ActionRequestLineTooLong:
+		return &refusal{status: http.StatusRequestURITooLong, action: action}
 	case action == requestlog.ActionRequestHeaderTooLarge:
 		return &refusal{
 			status: http.StatusRequestHeaderFieldsTooLarge,

internal/waf/waf.go

@@ -320,7 +320,7 @@ func asTheVisitorSentIt(r *http.Request, body []byte) *http.Request {
 }
 
 // allow answers a question with DispositionAllow and, while
-// SWW_WAF_ADD_LOOKUP_HEADERS is set, the client's AS number and country.
+// SWW_WAF_ADD_LOOKUP_HEADERS is true, the client's AS number and country.
 func (rq *request) allow() {
 	rq.allowed = true
 

internal/waf/waf_test.go

@@ -869,7 +869,7 @@ func TestAllowCarriesTheLookupHeadersWhileTheSettingIsSet(t *testing.T) {
 		wantASN, wantCountry string
 	}{
 		{on, "AS64496", "DE"},
-		{"false", "", ""},
+		{falseValue, "", ""},
 	} {
 		t.Run(tc.setting, func(t *testing.T) {
 			t.Parallel()
@@ -1690,7 +1690,12 @@ func TestALargeBodyAnnouncedAndLongHeadersAreNoReasonToRefuse(t *testing.T) {
 		strings.NewReader("a body"))
 	req.Header.Set(waf.ContentLengthHeader, "1073741824")
 	req.Header.Set(forwardedFor, otherClient)
-	req.Header.Set("X-Long", strings.Repeat("x", 40<<10))
+
+	// 40,000 bytes of headers, over rproxy's 32 KiB, in lines within the
+	// header limits.
+	for i := range 5 {
+		req.Header.Set("X-Long-"+strconv.Itoa(i), strings.Repeat("x", 8000))
+	}
 
 	got := do(t, req)
 	wantDisposition(t, got, http.StatusOK, waf.DispositionAllow)