waf: decide every visitor request within rproxy's timeout (closes #394)

The Core Rule Set is the one check whose time a visitor can stretch.
At paranoia level 4 it took over 2 s on a request with an 8 KiB
request line, three 8 KiB Cookie lines and a 64 KiB form body.
SWW_WAF_CORE_RULE_SET_BODY_INSPECTION_SIZE now takes at most 8K. The
Core Rule Set also reads no JSON body over 1 KiB, since Coraza turns
JSON into up to 8 times its size in names and values. That brings
such a request under 1 s.

A test per kind of input times the Core Rule Set on the worst request
within the limits, at the slowest settings. SPEC.md lists the limits
that bound it.

Model: opus-5-5

internal/coreruleset/coreruleset.go

@@ -481,12 +481,21 @@ func (c *CoreRuleSet) Inspect(
 	return Result{RuleIDs: ids, Score: score(tx)}, read, err
 }
 
+// mostJSONRead is the largest JSON body the Core Rule Set reads, even while
+// SWW_WAF_CORE_RULE_SET_BODY_INSPECTION_SIZE is larger. Coraza names each
+// value in a JSON body by the whole path to it, so what it gives the Core
+// Rule Set to read can outgrow the body: up to 8 times its size, and up to
+// 4 KiB for a small body. 1 KiB of JSON thus gives at most 8 KiB, no more
+// than the largest body of another kind.
+const mostJSONRead = 1 << 10
+
 // readBody reads body, the body of the request in tx, which has run on
 // the request's headers, while SWW_WAF_CORE_RULE_SET_BODY_INSPECTION_SIZE is
 // set and the body is of a kind the Core Rule Set reads: form data and
 // multipart, of which it reads the first c.bodyInspectionSize bytes, and
 // JSON and XML, which it reads only when they are no longer than that,
-// since they cannot be read in part.
+// since they cannot be read in part. The Core Rule Set reads no JSON body
+// longer than mostJSONRead either.
 // readBody reads one byte past c.bodyInspectionSize, to tell which they
 // are, gives the Core Rule Set what it reads, and returns what it read and
 // the error that ended the reading early, if one did.
@@ -499,6 +508,8 @@ func (c *CoreRuleSet) readBody(
 	}
 
 	inPart := false
+	// largest is the largest JSON or XML body the Core Rule Set reads.
+	largest := c.bodyInspectionSize
 	// How the body is read is a variable of the transaction, which only
 	// Coraza's interface for plugins reads.
 	state := tx.(plugintypes.TransactionState) //nolint:forcetypeassert // every one is
@@ -506,14 +517,16 @@ func (c *CoreRuleSet) readBody(
 	switch state.Variables().RequestBodyProcessor().Get() {
 	case "URLENCODED", "MULTIPART":
 		inPart = true
-	case "JSON", "XML":
+	case "JSON":
+		largest = min(largest, mostJSONRead)
+	case "XML":
 	default:
 		return nil, nil
 	}
 
 	read, err := io.ReadAll(io.LimitReader(body, c.bodyInspectionSize+1))
 
-	if inPart || (err == nil && int64(len(read)) <= c.bodyInspectionSize) {
+	if inPart || (err == nil && int64(len(read)) <= largest) {
 		// Coraza holds what it reads of the body in memory, up to the
 		// limit, so this cannot fail.
 		_, _, _ = tx.WriteRequestBody(read)

internal/coreruleset/coreruleset_test.go

@@ -390,22 +390,15 @@ func TestMoreParametersThanCorazaKeepsIsAMatch(t *testing.T) {
 		matched(900300),
 	)
 
-	// So it is with the fields of a form data or JSON body.
+	// So it is with the fields of a form data body. A JSON body the Core
+	// Rule Set reads, of at most mostJSONRead bytes, cannot hold that many.
 	crs = readingBodies(t)
 
-	for _, tc := range []struct{ header, body string }{
-		{formData, strings.Repeat("a=1&", 999) + attack},
-		{jsonBody, `{"a":[` + strings.Repeat("1,", 998) + `1],"id":"` + injection + `"}`},
-	} {
-		wantBody(t, crs, post(tc.header), tc.body, matched(942100), tc.body)
-	}
+	body := strings.Repeat("a=1&", 999) + attack
+	wantBody(t, crs, post(formData), body, matched(942100), body)
 
-	for _, tc := range []struct{ header, body string }{
-		{formData, strings.Repeat("a=1&", 1000) + attack},
-		{jsonBody, `{"a":[` + strings.Repeat("1,", 999) + `1],"id":"` + injection + `"}`},
-	} {
-		wantBody(t, crs, post(tc.header), tc.body, matched(900300), tc.body)
-	}
+	body = strings.Repeat("a=1&", 1000) + attack
+	wantBody(t, crs, post(formData), body, matched(900300), body)
 }
 
 func TestRedirectURIMayNameALocalAddress(t *testing.T) {
@@ -1512,13 +1505,15 @@ const (
 	wpTags    = "/wp-json/wp/v2/tags"
 )
 
-// readingBodiesUpTo64K returns the Core Rule Set as sww runs it by default,
+// readingBodiesUpTo8K returns the Core Rule Set as sww runs it by default,
 // but reading bodies up to the largest SWW_WAF_CORE_RULE_SET_BODY_INSPECTION_SIZE.
-func readingBodiesUpTo64K(t *testing.T) *coreruleset.CoreRuleSet {
+func readingBodiesUpTo8K(t *testing.T) *coreruleset.CoreRuleSet {
 	t.Helper()
 
 	return shared(t, coreruleset.Params{
-		ParanoiaLevel: 1, DisabledRules: defaultDisabledRules, BodyInspectionSize: 64<<10 - 1,
+		ParanoiaLevel:      1,
+		DisabledRules:      defaultDisabledRules,
+		BodyInspectionSize: mostBodyRead,
 	})
 }
 
@@ -1582,7 +1577,7 @@ func TestWordPressAttacksAreRefused(t *testing.T) {
 
 	const threshold = 5 // SWW_WAF_CORE_RULE_SET_SCORE_THRESHOLD's default
 
-	defaults, bodies := atDefaults(t), readingBodiesUpTo64K(t)
+	defaults, bodies := atDefaults(t), readingBodiesUpTo8K(t)
 
 	for _, attack := range []string{
 		sqlInjection,
@@ -1693,7 +1688,7 @@ func wordpressRESTAddresses(route string) []string {
 func TestWordPressExclusionsFollowEveryRESTAddress(t *testing.T) {
 	t.Parallel()
 
-	crs := readingBodiesUpTo64K(t)
+	crs := readingBodiesUpTo8K(t)
 	content := `{"content":"` + wordpressBlock + `"}`
 
 	for _, route := range []string{
@@ -1919,7 +1914,7 @@ func TestWordPressCommandAfterASeparatorIsRefusedOnSearchesAndNames(
 		wantResult(t, crs, get(target+command), matched(932235))
 	}
 
-	bodies := readingBodiesUpTo64K(t)
+	bodies := readingBodiesUpTo8K(t)
 
 	for _, p := range wordpressBodyFields(command) {
 		r := request{http.MethodPost, p.target, []string{p.contentType}}
@@ -2143,7 +2138,7 @@ func TestWordPressBodyFieldsAreCheckedInTheQuery(t *testing.T) {
 func TestWordPressBodyNamesAndAddressesAreExcludedOnlyThere(t *testing.T) {
 	t.Parallel()
 
-	crs := readingBodiesUpTo64K(t)
+	crs := readingBodiesUpTo8K(t)
 
 	for _, v := range wordpressWords() {
 		for _, field := range []string{"title", "excerpt", "name"} {
@@ -2262,7 +2257,7 @@ func TestWordPressExclusionsAreNarrow(t *testing.T) {
 		length  = "Content-Length: 2"
 	)
 
-	crs := readingBodiesUpTo64K(t)
+	crs := readingBodiesUpTo8K(t)
 	saving := request{
 		http.MethodPost,
 		wpPost,
@@ -2473,19 +2468,35 @@ func TestFormDataAndMultipartAreReadUpToTheLimit(t *testing.T) {
 func TestJSONAndXMLAreReadOnlyWhenNoLargerThanTheLimit(t *testing.T) {
 	t.Parallel()
 
-	crs := readingBodies(t)
+	// The limit is the body inspection size, but at most mostJSONRead for
+	// JSON. smallSize is a body inspection size under mostJSONRead.
+	const smallSize = 512
 
-	for _, tc := range []struct{ header, head, tail string }{
-		{jsonBody, `{"q":"` + injection + `","pad":"`, `"}`},
-		{xmlBody, "<r><q>" + injection + "</q><pad>", "</pad></r>"},
+	bodies, smallBodies := readingBodies(t), shared(t, coreruleset.Params{
+		ParanoiaLevel: 1, DisabledRules: defaultDisabledRules,
+		BodyInspectionSize: smallSize,
+	})
+	jsonHead, jsonTail := `{"q":"`+injection+`","pad":"`, `"}`
+
+	for _, tc := range []struct {
+		crs                *coreruleset.CoreRuleSet
+		header, head, tail string
+		limit              int
+	}{
+		{bodies, jsonBody, jsonHead, jsonTail, mostJSONRead},
+		{smallBodies, jsonBody, jsonHead, jsonTail, smallSize},
+		{
+			bodies, xmlBody, "<r><q>" + injection + "</q><pad>", "</pad></r>",
+			bodyInspectionSize,
+		},
 	} {
-		fits := padded(tc.head, tc.tail, bodyInspectionSize)
-		wantBody(t, crs, post(tc.header), fits, matched(942100), fits)
+		fits := padded(tc.head, tc.tail, tc.limit)
+		wantBody(t, tc.crs, post(tc.header), fits, matched(942100), fits)
 
-		larger := padded(tc.head, tc.tail, bodyInspectionSize+1)
+		larger := padded(tc.head, tc.tail, tc.limit+1)
 		wantBody(
 			t,
-			crs,
+			tc.crs,
 			post(tc.header),
 			larger,
 			coreruleset.Result{},

internal/coreruleset/inspectiontime_test.go

@@ -0,0 +1,371 @@
+package coreruleset_test
+
+import (
+	"maps"
+	"net/http"
+	"net/http/httptest"
+	"net/netip"
+	"slices"
+	"strconv"
+	"strings"
+	"testing"
+	"time"
+
+	"sneak.berlin/go/smallwebwaf/internal/coreruleset"
+)
+
+// The bounds on what a visitor can send, as SPEC.md gives them.
+const (
+	// lineLimit is the longest request line or header line.
+	lineLimit = 8 << 10
+	// headerLimit is the most bytes rproxy reads of a request line and
+	// headers together.
+	headerLimit = 32 << 10
+	// mostCookies and mostHeaderFields are waf's limits on cookies and header
+	// fields.
+	mostCookies      = 50
+	mostHeaderFields = 100
+	// mostBodyRead is the largest SWW_WAF_CORE_RULE_SET_BODY_INSPECTION_SIZE.
+	mostBodyRead = 8 << 10
+	// mostJSONRead is the largest JSON body the Core Rule Set reads.
+	mostJSONRead = 1 << 10
+)
+
+// inspectionTimeLimit is the most time the Core Rule Set may take on one
+// request. It is the default of rproxy's SWW_RPROXY_WAF_BACKEND_TIMEOUT_MS, 2
+// seconds, less the default of SWW_WAF_ASN_AND_COUNTRY_LOOKUP_TIMEOUT_MS, 800
+// milliseconds, which a question can also wait for GeoJS, and less 200
+// milliseconds for waf's other checks.
+const inspectionTimeLimit = time.Second
+
+// text returns n bytes of letters, digits and spaces, which the Core Rule Set
+// takes longer over than one letter repeated.
+func text(n int) string {
+	const words = "select 0x2f from tbl_1 where name like abc_9 "
+
+	return strings.Repeat(words, n/len(words)+1)[:n]
+}
+
+// visitorRequest is a request a visitor can send, at the most of one or more
+// of the bounds above.
+type visitorRequest struct {
+	name   string
+	target string
+	// header holds the headers besides Host.
+	header http.Header
+	// contentType is the body's type, "" for no body.
+	contentType string
+	body        string
+}
+
+// longestTarget returns a target whose request line, "POST <target>
+// HTTP/1.1", is lineLimit bytes long.
+func longestTarget() string {
+	const around = len("POST /?q= HTTP/1.1")
+
+	return "/?q=" + strings.ReplaceAll(text(lineLimit-around), " ", "+")
+}
+
+// cookieLine returns a Cookie value whose line, "Cookie: <value>", is
+// lineLimit bytes long, made of count cookies.
+func cookieLine(count int) string {
+	const linePrefix = len("Cookie: ")
+
+	cookies := make([]string, count)
+	for i := range cookies {
+		cookies[i] = "c" + strconv.Itoa(i) + "="
+	}
+
+	// Each cookie is followed by "; ", but for the last.
+	room := lineLimit - linePrefix - len(strings.Join(cookies, "; "))
+	for i := range cookies {
+		share := room / count
+		if i == 0 {
+			share += room % count
+		}
+
+		cookies[i] += strings.ReplaceAll(text(share), " ", "_")
+	}
+
+	return strings.Join(cookies, "; ")
+}
+
+// headerValue returns a value whose line, "<name>: <value>", is n bytes long.
+func headerValue(name string, n int) string {
+	return text(n - len(name) - len(": "))
+}
+
+// formFields returns a form body of mostBodyRead bytes holding count fields.
+func formFields(count int) string {
+	fields := make([]string, count)
+	for i := range fields {
+		fields[i] = "f" + strconv.Itoa(i) + "="
+	}
+
+	room := mostBodyRead - len(strings.Join(fields, "&"))
+	for i := range fields {
+		share := room / count
+		if i == 0 {
+			share += room % count
+		}
+
+		fields[i] += strings.ReplaceAll(text(share), " ", "+")
+	}
+
+	return strings.Join(fields, "&")
+}
+
+// multipartBody returns a multipart body of mostBodyRead bytes, with the
+// boundary "b", holding fields of about size bytes each.
+func multipartBody(size int) string {
+	var body strings.Builder
+
+	const end = "--b--\r\n"
+
+	for i := 0; ; i++ {
+		head := "--b\r\nContent-Disposition: form-data; name=\"f" +
+			strconv.Itoa(i) + "\"\r\n\r\n"
+
+		room := mostBodyRead - body.Len() - len(
+			end,
+		) - len(
+			head,
+		) - len(
+			"\r\n",
+		)
+		if room <= 0 {
+			break
+		}
+
+		body.WriteString(head + text(min(size, room)) + "\r\n")
+	}
+
+	body.WriteString(end)
+
+	return body.String()
+}
+
+// jsonArrayOfMostElements returns a JSON array of at most mostJSONRead bytes
+// holding as many elements as fit, each the number 1.
+func jsonArrayOfMostElements() string {
+	return "[1" + strings.Repeat(
+		",1",
+		(mostJSONRead-len("[1]"))/len(",1"),
+	) + "]"
+}
+
+// jsonOfMostElementsUnderAKey returns a JSON body of mostJSONRead bytes
+// holding as many elements as fit, each the number 1, in an array under a
+// key of 6 bytes. Coraza names each element "json.<key>.<index>", so a
+// longer key makes longer names. 6 bytes is the longest key that keeps the
+// names and values of this body within the 8 KiB Coraza allows.
+func jsonOfMostElementsUnderAKey() string {
+	head := `{"` + text(6) + `":[1`
+
+	return head + strings.Repeat(
+		",1",
+		(mostJSONRead-len(head+"]}"))/len(",1"),
+	) + "]}"
+}
+
+// The kinds of body the Core Rule Set reads, and the header that names a
+// request's cookies.
+const (
+	formType      = "application/x-www-form-urlencoded"
+	jsonType      = "application/json"
+	multipartType = "multipart/form-data; boundary=b"
+	cookieHeader  = "Cookie"
+)
+
+// fullLine is the length of each of the request line and the three or four
+// header lines that together fill rproxy's limit, with room for the line
+// endings and the other headers.
+const fullLine = lineLimit - 64
+
+// worstCaseRequests are, for each kind of thing a visitor sends, the requests
+// that keep the Core Rule Set busiest, within the bounds above. The last
+// holds the most of everything at once: Cookie lines keep it busier than
+// other header lines, and the JSON body of the most elements under a key
+// keeps it busier than the other bodies.
+func worstCaseRequests() []visitorRequest {
+	fullCookieLine := cookieLine(1)[:fullLine-len("Cookie: ")]
+
+	return append(
+		append(worstCaseHeaders(), worstCaseBodies()...),
+		visitorRequest{
+			name:   "the longest request line, three Cookie lines and body",
+			target: longestTarget()[:fullLine-len("POST  HTTP/1.1")],
+			header: http.Header{cookieHeader: {
+				fullCookieLine, fullCookieLine, fullCookieLine,
+			}},
+			contentType: jsonType, body: jsonOfMostElementsUnderAKey(),
+		},
+	)
+}
+
+// worstCaseHeaders are the requests of worstCaseRequests with no body.
+func worstCaseHeaders() []visitorRequest {
+	headerFields := http.Header{}
+
+	for i := range mostHeaderFields - 1 {
+		name := "X-Field-" + strconv.Itoa(i)
+		headerFields.Set(
+			name,
+			headerValue(name, headerLimit/mostHeaderFields),
+		)
+	}
+
+	return []visitorRequest{
+		{name: "the longest request line", target: longestTarget()},
+		{
+			name: "the longest request line, as query parameters",
+			target: "/?" + strings.Repeat(
+				"a=1&",
+				(lineLimit-len("POST /? HTTP/1.1"))/len("a=1&"),
+			),
+		},
+		{
+			name:   "the longest Cookie line, as one cookie",
+			target: "/",
+			header: http.Header{cookieHeader: {cookieLine(1)}},
+		},
+		{
+			name:   "the longest Cookie line, as the most cookies",
+			target: "/",
+			header: http.Header{cookieHeader: {cookieLine(mostCookies)}},
+		},
+		{name: "the most header fields", target: "/", header: headerFields},
+		{
+			name:   "the longest header lines",
+			target: "/",
+			header: http.Header{
+				"User-Agent": {headerValue("User-Agent", fullLine)},
+				"Referer":    {headerValue("Referer", fullLine)},
+				"Accept":     {headerValue("Accept", fullLine)},
+				"X-Long":     {headerValue("X-Long", fullLine)},
+			},
+		},
+	}
+}
+
+// worstCaseBodies are the requests of worstCaseRequests whose body holds
+// the most the Core Rule Set reads.
+func worstCaseBodies() []visitorRequest {
+	const nested = (mostJSONRead - len(`{"a":1}`)) / len(`{"a":}`)
+
+	return []visitorRequest{
+		{
+			name: "a form body of one field", target: "/",
+			contentType: formType, body: formFields(1),
+		},
+		{
+			name: "a form body of the most fields Coraza keeps", target: "/",
+			contentType: formType, body: formFields(1000),
+		},
+		{
+			name: "a JSON body of one string", target: "/",
+			contentType: jsonType,
+			body: `{"a":"` + text(
+				mostJSONRead-len(`{"a":""}`),
+			) + `"}`,
+		},
+		{
+			name: "a JSON body of the most elements", target: "/",
+			contentType: jsonType, body: jsonArrayOfMostElements(),
+		},
+		{
+			name: "a JSON body of the most elements under a key", target: "/",
+			contentType: jsonType, body: jsonOfMostElementsUnderAKey(),
+		},
+		{
+			name: "a JSON body nested deep", target: "/",
+			contentType: jsonType,
+			body: strings.Repeat(`{"a":`, nested) + "1" +
+				strings.Repeat("}", nested),
+		},
+		{
+			name: "an XML body of many elements", target: "/",
+			contentType: "application/xml",
+			body: "<a>" + strings.Repeat(
+				"<b>x</b>",
+				(mostBodyRead-len("<a></a>"))/len("<b>x</b>"),
+			) + "</a>",
+		},
+		{
+			name: "a multipart body of one field", target: "/",
+			contentType: multipartType, body: multipartBody(mostBodyRead),
+		},
+		{
+			name: "a multipart body of many fields", target: "/",
+			contentType: multipartType, body: multipartBody(1),
+		},
+	}
+}
+
+// inspectionTime returns how long crs takes to inspect tc, and fails t unless
+// it reads all of tc's body and Coraza parses it.
+func inspectionTime(
+	t *testing.T, crs *coreruleset.CoreRuleSet, tc visitorRequest,
+) time.Duration {
+	t.Helper()
+
+	req := httptest.NewRequestWithContext(
+		t.Context(), http.MethodPost, tc.target, nil,
+	)
+	maps.Copy(req.Header, tc.header)
+
+	if tc.contentType != "" {
+		req.Header.Set("Content-Type", tc.contentType)
+	}
+
+	began := time.Now()
+	result, read, _ := crs.Inspect(
+		req, netip.MustParseAddr("192.0.2.1"), strings.NewReader(tc.body),
+	)
+	took := time.Since(began)
+
+	if string(read) != tc.body {
+		t.Errorf("read %d bytes of %d", len(read), len(tc.body))
+	}
+
+	// Rule 900440 matches a body Coraza could not parse.
+	if slices.Contains(result.RuleIDs, 900440) {
+		t.Errorf("Coraza could not parse the body")
+	}
+
+	return took
+}
+
+// TestTheCoreRuleSetInspectsEachWorstCaseRequestInTime runs one at a time, so
+// that the tests running in parallel do not slow it. Other work on the host
+// can still slow one try, so a request fails only when three tries in a row
+// take too long.
+//
+//nolint:paralleltest // one at a time, as above
+func TestTheCoreRuleSetInspectsEachWorstCaseRequestInTime(t *testing.T) {
+	const tries = 3
+
+	// The settings that make the Core Rule Set slowest: the highest paranoia
+	// level, no rule switched off, and the most of a body read.
+	crs := shared(t, coreruleset.Params{
+		ParanoiaLevel: 4, BodyInspectionSize: mostBodyRead,
+	})
+
+	for _, tc := range worstCaseRequests() {
+		t.Run(tc.name, func(t *testing.T) {
+			var took time.Duration
+
+			for range tries {
+				took = inspectionTime(t, crs, tc)
+				if took <= inspectionTimeLimit {
+					return
+				}
+			}
+
+			t.Errorf(
+				"took %s on the last of %d tries, over %s",
+				took, tries, inspectionTimeLimit,
+			)
+		})
+	}
+}