http2: close connections when receiving too many headers

Maintaining HPACK state requires that we parse and process
all HEADERS and CONTINUATION frames on a connection.
When a request's headers exceed MaxHeaderBytes, we don't
allocate memory to store the excess headers but we do
parse them. This permits an attacker to cause an HTTP/2
endpoint to read arbitrary amounts of data, all associated
with a request which is going to be rejected.

Set a limit on the amount of excess header frames we
will process before closing a connection.

Thanks to Bartek Nowotarski for reporting this issue.

Fixes CVE-2023-45288
Fixes golang/go#65051

Change-Id: I15df097268df13bb5a9e9d3a5c04a8a141d850f6
Reviewed-on: https://team-review.git.corp.google.com/c/golang/go-private/+/2130527
Reviewed-by: Roland Shoemaker <bracewell@google.com>
Reviewed-by: Tatiana Bradley <tatianabradley@google.com>
Reviewed-on: https://go-review.googlesource.com/c/net/+/576155
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

http2/frame.go

@@ -1564,6 +1564,7 @@ func (fr *Framer) readMetaFrame(hf *HeadersFrame) (*MetaHeadersFrame, error) {
 		if size > remainSize {
 			hdec.SetEmitEnabled(false)
 			mh.Truncated = true
+			remainSize = 0
 			return
 		}
 		remainSize -= size
@@ -1576,6 +1577,36 @@ func (fr *Framer) readMetaFrame(hf *HeadersFrame) (*MetaHeadersFrame, error) {
 	var hc headersOrContinuation = hf
 	for {
 		frag := hc.HeaderBlockFragment()
+
+		// Avoid parsing large amounts of headers that we will then discard.
+		// If the sender exceeds the max header list size by too much,
+		// skip parsing the fragment and close the connection.
+		//
+		// "Too much" is either any CONTINUATION frame after we've already
+		// exceeded the max header list size (in which case remainSize is 0),
+		// or a frame whose encoded size is more than twice the remaining
+		// header list bytes we're willing to accept.
+		if int64(len(frag)) > int64(2*remainSize) {
+			if VerboseLogs {
+				log.Printf("http2: header list too large")
+			}
+			// It would be nice to send a RST_STREAM before sending the GOAWAY,
+			// but the struture of the server's frame writer makes this difficult.
+			return nil, ConnectionError(ErrCodeProtocol)
+		}
+
+		// Also close the connection after any CONTINUATION frame following an
+		// invalid header, since we stop tracking the size of the headers after
+		// an invalid one.
+		if invalid != nil {
+			if VerboseLogs {
+				log.Printf("http2: invalid header: %v", invalid)
+			}
+			// It would be nice to send a RST_STREAM before sending the GOAWAY,
+			// but the struture of the server's frame writer makes this difficult.
+			return nil, ConnectionError(ErrCodeProtocol)
+		}
+
 		if _, err := hdec.Write(frag); err != nil {
 			return nil, ConnectionError(ErrCodeCompression)
 		}

http2/server_test.go

@@ -4786,3 +4786,87 @@ Frames:
 		close(s)
 	}
 }
+
+func TestServerContinuationFlood(t *testing.T) {
+	st := newServerTester(t, func(w http.ResponseWriter, r *http.Request) {
+		fmt.Println(r.Header)
+	}, func(ts *httptest.Server) {
+		ts.Config.MaxHeaderBytes = 4096
+	})
+	defer st.Close()
+
+	st.writePreface()
+	st.writeInitialSettings()
+	st.writeSettingsAck()
+
+	st.writeHeaders(HeadersFrameParam{
+		StreamID:      1,
+		BlockFragment: st.encodeHeader(),
+		EndStream:     true,
+	})
+	for i := 0; i < 1000; i++ {
+		st.fr.WriteContinuation(1, false, st.encodeHeaderRaw(
+			fmt.Sprintf("x-%v", i), "1234567890",
+		))
+	}
+	st.fr.WriteContinuation(1, true, st.encodeHeaderRaw(
+		"x-last-header", "1",
+	))
+
+	var sawGoAway bool
+	for {
+		f, err := st.readFrame()
+		if err != nil {
+			break
+		}
+		switch f.(type) {
+		case *GoAwayFrame:
+			sawGoAway = true
+		case *HeadersFrame:
+			t.Fatalf("received HEADERS frame; want GOAWAY")
+		}
+	}
+	if !sawGoAway {
+		t.Errorf("connection closed with no GOAWAY frame; want one")
+	}
+}
+
+func TestServerContinuationAfterInvalidHeader(t *testing.T) {
+	st := newServerTester(t, func(w http.ResponseWriter, r *http.Request) {
+		fmt.Println(r.Header)
+	})
+	defer st.Close()
+
+	st.writePreface()
+	st.writeInitialSettings()
+	st.writeSettingsAck()
+
+	st.writeHeaders(HeadersFrameParam{
+		StreamID:      1,
+		BlockFragment: st.encodeHeader(),
+		EndStream:     true,
+	})
+	st.fr.WriteContinuation(1, false, st.encodeHeaderRaw(
+		"x-invalid-header", "\x00",
+	))
+	st.fr.WriteContinuation(1, true, st.encodeHeaderRaw(
+		"x-valid-header", "1",
+	))
+
+	var sawGoAway bool
+	for {
+		f, err := st.readFrame()
+		if err != nil {
+			break
+		}
+		switch f.(type) {
+		case *GoAwayFrame:
+			sawGoAway = true
+		case *HeadersFrame:
+			t.Fatalf("received HEADERS frame; want GOAWAY")
+		}
+	}
+	if !sawGoAway {
+		t.Errorf("connection closed with no GOAWAY frame; want one")
+	}
+}