http2: limit number of rejected stream openings

Limit the number of streams that are rejected upon creation. Since
each such rejection is associated with an `NGHTTP2_ENHANCE_YOUR_CALM`
error that should tell the peer to not open any more streams,
continuing to open streams should be read as a sign of a misbehaving
peer. The limit is currently set to 100 but could be changed or made
configurable.

This is intended to mitigate CVE-2019-9514.

Backport-PR-URL: #29123
PR-URL: #29122
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

src/node_http2.cc

@@ -6,6 +6,8 @@
 #include "node_http2_state.h"
 #include "node_internals.h"
 #include "node_perf.h"
+#include "node_revert.h"
+#include "util-inl.h"
 
 #include <algorithm>
 
@@ -921,11 +923,17 @@ int Http2Session::OnBeginHeadersCallback(nghttp2_session* handle,
     if (UNLIKELY(!session->CanAddStream() ||
                  Http2Stream::New(session, id, frame->headers.cat) ==
                      nullptr)) {
+      if (session->rejected_stream_count_++ > 100 &&
+          !IsReverted(SECURITY_REVERT_CVE_2019_9514)) {
+        return NGHTTP2_ERR_CALLBACK_FAILURE;
+      }
       // Too many concurrent streams being opened
       nghttp2_submit_rst_stream(**session, NGHTTP2_FLAG_NONE, id,
                                 NGHTTP2_ENHANCE_YOUR_CALM);
       return NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE;
     }
+
+    session->rejected_stream_count_ = 0;
   } else if (!stream->IsDestroyed()) {
     stream->StartHeaders(frame->headers.cat);
   }

src/node_http2.h

@@ -1017,6 +1017,11 @@ class Http2Session : public AsyncWrap, public StreamListener {
   std::vector<nghttp2_stream_write> outgoing_buffers_;
   std::vector<uint8_t> outgoing_storage_;
   std::vector<int32_t> pending_rst_streams_;
+  // Count streams that have been rejected while being opened. Exceeding a fixed
+  // limit will result in the session being destroyed, as an indication of a
+  // misbehaving peer. This counter is reset once new streams are being
+  // accepted again.
+  int32_t rejected_stream_count_ = 0;
 
   void CopyDataIntoOutgoing(const uint8_t* src, size_t src_length);
   void ClearOutgoing(int status);

src/node_revert.h

@@ -15,8 +15,11 @@
  **/
 namespace node {
 
-#define SECURITY_REVERSIONS(XX)
+#define SECURITY_REVERSIONS(XX)                                            \
+  XX(CVE_2019_9514, "CVE-2019-9514", "HTTP/2 Reset Flood")                 \
 //  XX(CVE_2016_PEND, "CVE-2016-PEND", "Vulnerability Title")
+  // TODO(addaleax): Remove all of the above before Node.js 13 as the comment
+  // at the start of the file indicates.
 
 enum reversion {
 #define V(code, ...) SECURITY_REVERT_##code,