http2: handle server errors after sending GOAWAY

The HTTP/2 server uses serverConn.goAwayCode to track whether a
connection has encountered a fatal error. If an error is encountered
after sending a ErrCodeNo GOAWAY, upgrade goAwayCode to reflect the
error status of the connection.

Fixes an issue where a server connection could hang forever waiting
for a clean shutdown that was preempted by a subsequent fatal error.

Fixes CVE-2022-27664
For golang/go#53977

Change-Id: I165b81ab53176c77a68c42976030499d57bb05d3
Reviewed-on: https://team-review.git.corp.google.com/c/golang/go-private/+/1413887
Reviewed-by: Damien Neil <dneil@google.com>
Reviewed-by: Roland Shoemaker <bracewell@google.com>
Reviewed-on: https://go-review.googlesource.com/c/net/+/428735
Run-TryBot: Damien Neil <dneil@google.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>

http2/server.go

@@ -1371,6 +1371,9 @@ func (sc *serverConn) startGracefulShutdownInternal() {
 func (sc *serverConn) goAway(code ErrCode) {
 	sc.serveG.check()
 	if sc.inGoAway {
+		if sc.goAwayCode == ErrCodeNo {
+			sc.goAwayCode = code
+		}
 		return
 	}
 	sc.inGoAway = true

http2/server_test.go

@@ -4366,3 +4366,46 @@ func TestServerSendsEarlyHints(t *testing.T) {
 		}
 	})
 }
+
+func TestProtocolErrorAfterGoAway(t *testing.T) {
+	st := newServerTester(t, func(w http.ResponseWriter, r *http.Request) {
+		io.Copy(io.Discard, r.Body)
+	})
+	defer st.Close()
+
+	st.greet()
+	content := "some content"
+	st.writeHeaders(HeadersFrameParam{
+		StreamID: 1,
+		BlockFragment: st.encodeHeader(
+			":method", "POST",
+			"content-length", strconv.Itoa(len(content)),
+		),
+		EndStream:  false,
+		EndHeaders: true,
+	})
+	st.writeData(1, false, []byte(content[:5]))
+
+	_, err := st.readFrame()
+	if err != nil {
+		st.t.Fatal(err)
+	}
+
+	// Send a GOAWAY with ErrCodeNo, followed by a bogus window update.
+	// The server should close the connection.
+	if err := st.fr.WriteGoAway(1, ErrCodeNo, nil); err != nil {
+		t.Fatal(err)
+	}
+	if err := st.fr.WriteWindowUpdate(0, 1<<31-1); err != nil {
+		t.Fatal(err)
+	}
+
+	for {
+		if _, err := st.readFrame(); err != nil {
+			if err != io.EOF {
+				t.Errorf("unexpected readFrame error: %v", err)
+			}
+			break
+		}
+	}
+}