http2: allow security revert for Ping/Settings Flood

nghttp2 has updated its limit for outstanding Ping/Settings ACKs
to 1000. This commit allows reverting to the old default of 10000.

The associated CVEs are CVE-2019-9512/CVE-2019-9515.

Backport-PR-URL: #29124
PR-URL: #29122
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

src/node_http2.cc

@@ -144,6 +144,9 @@ Http2Options::Http2Options(Environment* env, nghttp2_session_type type) {
         buffer[IDX_OPTIONS_PEER_MAX_CONCURRENT_STREAMS]);
   }
 
+  if (IsReverted(SECURITY_REVERT_CVE_2019_9512))
+    nghttp2_option_set_max_outbound_ack(options_, 10000);
+
   // The padding strategy sets the mechanism by which we determine how much
   // additional frame padding to apply to DATA and HEADERS frames. Currently
   // this is set on a per-session basis, but eventually we may switch to

src/node_revert.h

@@ -17,6 +17,7 @@ namespace node {
 
 #define SECURITY_REVERSIONS(XX) \
   XX(CVE_2018_12116, "CVE-2018-12116", "HTTP request splitting")           \
+  XX(CVE_2019_9512, "CVE-2019-9512", "HTTP/2 Ping/Settings Flood")         \
   XX(CVE_2019_9514, "CVE-2019-9514", "HTTP/2 Reset Flood")                 \
   XX(CVE_2019_9516, "CVE-2019-9516", "HTTP/2 0-Length Headers Leak")       \
   XX(CVE_2019_9518, "CVE-2019-9518", "HTTP/2 Empty DATA Frame Flooding")   \