http2: stop reading from socket if writes are in progress

addaleax · BethGriggs · commit 854dba649e82 · 2019-08-15T17:38:23.000+01:00
If a write to the underlying socket finishes asynchronously, that means that we cannot write any more data at that point without waiting for it to finish. If this happens, we should also not be producing any more input. This is part of mitigating CVE-2019-9511/CVE-2019-9517. Backport-PR-URL: #29124 PR-URL: #29122 Reviewed-By: Rich Trott <rtrott@gmail.com> Reviewed-By: James M Snell <jasnell@gmail.com>
diff --git a/src/node_http2.cc b/src/node_http2.cc
@@ -1585,9 +1585,18 @@ void Http2Session::OnStreamAfterWriteImpl(WriteWrap* w, int status, void* ctx) {
   Http2Session* session = static_cast<Http2Session*>(ctx);
   DEBUG_HTTP2SESSION2(session, "write finished with status %d", status);
 
+  CHECK_NE(session->flags_ & SESSION_STATE_WRITE_IN_PROGRESS, 0);
+  session->flags_ &= ~SESSION_STATE_WRITE_IN_PROGRESS;
+
   // Inform all pending writes about their completion.
   session->ClearOutgoing(status);
 
+  if ((session->flags_ & SESSION_STATE_READING_STOPPED) &&
+      nghttp2_session_want_read(session->session_)) {
+    session->flags_ &= ~SESSION_STATE_READING_STOPPED;
+    session->stream_->ReadStart();
+  }
+
   if (!(session->flags_ & SESSION_STATE_WRITE_SCHEDULED)) {
     // Schedule a new write if nghttp2 wants to send data.
     session->MaybeScheduleWrite();
@@ -1627,10 +1636,13 @@ void Http2Session::MaybeScheduleWrite() {
 }
 
 void Http2Session::MaybeStopReading() {
+  if (flags_ & SESSION_STATE_READING_STOPPED) return;
   int want_read = nghttp2_session_want_read(session_);
   DEBUG_HTTP2SESSION2(this, "wants read? %d", want_read);
-  if (want_read == 0)
+  if (want_read == 0 || (flags_ & SESSION_STATE_WRITE_IN_PROGRESS)) {
+    flags_ |= SESSION_STATE_READING_STOPPED;
     stream_->ReadStop();
+  }
 }
 
 // Unset the sending state, finish up all current writes, and reset
@@ -1757,6 +1769,8 @@ uint8_t Http2Session::SendPendingData() {
 
   chunks_sent_since_last_write_++;
 
+  CHECK_EQ(flags_ & SESSION_STATE_WRITE_IN_PROGRESS, 0);
+
   // DoTryWrite may modify both the buffer list start itself and the
   // base pointers/length of the individual buffers.
   uv_buf_t* writebufs = *bufs;
@@ -1766,8 +1780,11 @@ uint8_t Http2Session::SendPendingData() {
     return 0;
   }
 
+  flags_ |= SESSION_STATE_WRITE_IN_PROGRESS;
+
   WriteWrap* req = AllocateSend();
   if (stream_->DoWrite(req, writebufs, count, nullptr) != 0) {
+    flags_ &= ~SESSION_STATE_WRITE_IN_PROGRESS;
     req->Dispose();
   }
 
diff --git a/src/node_http2.h b/src/node_http2.h
@@ -384,6 +384,8 @@ enum session_state_flags {
   SESSION_STATE_CLOSED = 0x4,
   SESSION_STATE_CLOSING = 0x8,
   SESSION_STATE_SENDING = 0x10,
+  SESSION_STATE_WRITE_IN_PROGRESS = 0x20,
+  SESSION_STATE_READING_STOPPED = 0x40,
 };
 
 // This allows for 4 default-sized frames with their frame headers
