http2: treat non-EOF empty frames like other invalid frames

Use the existing mechanism that we have to keep track of invalid frames
for treating this specific kind of invalid frame.

The commit that originally introduced this check was 695e38b,
which was supposed to proected against CVE-2019-9518, which in turn
was specifically about a *flood* of empty data frames. While these are
still invalid frames either way, it makes sense to be forgiving here
and just treat them like other invalid frames, i.e. to allow a small
(configurable) number of them.

Fixes: #37849

PR-URL: #37875
Backport-PR-URL: #38673
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

Author: addaleax

src/node_http2.cc

@@ -1277,7 +1277,11 @@ int Http2Session::HandleDataFrame(const nghttp2_frame* frame) {
       frame->hd.flags & NGHTTP2_FLAG_END_STREAM) {
     stream->EmitRead(UV_EOF);
   } else if (frame->hd.length == 0) {
-    return 1;  // Consider 0-length frame without END_STREAM an error.
+    if (invalid_frame_count_++ > js_fields_->max_invalid_frames) {
+      Debug(this, "rejecting empty-frame-without-END_STREAM flood\n");
+      // Consider a flood of 0-length frames without END_STREAM an error.
+      return 1;
+    }
   }
   return 0;
 }

test/fixtures/emptyframe.http2

@@ -0,0 +1,39 @@
+'use strict';
+const common = require('../common');
+if (!common.hasCrypto)
+  common.skip('missing crypto');
+const { readSync } = require('../common/fixtures');
+const net = require('net');
+const http2 = require('http2');
+const { once } = require('events');
+
+async function main() {
+  const blobWithEmptyFrame = readSync('emptyframe.http2');
+  const server = net.createServer((socket) => {
+    socket.end(blobWithEmptyFrame);
+  }).listen(0);
+  await once(server, 'listening');
+
+  for (const maxSessionInvalidFrames of [0, 2]) {
+    const client = http2.connect(`http://localhost:${server.address().port}`, {
+      maxSessionInvalidFrames
+    });
+    const stream = client.request({
+      ':method': 'GET',
+      ':path': '/'
+    });
+    if (maxSessionInvalidFrames) {
+      stream.on('error', common.mustNotCall());
+      client.on('error', common.mustNotCall());
+    } else {
+      stream.on('error', common.mustCall());
+      client.on('error', common.mustCall());
+    }
+    stream.resume();
+    await once(stream, 'end');
+    client.close();
+  }
+  server.close();
+}
+
+main().then(common.mustCall());