Fix HTTP/2 CVEs

A number of HTTP/2 CVEs were documented recently:

  https://www.kb.cert.org/vuls/id/605641/

This commit, along with a few changes and additions in Cowlib,
fix or improve protection against all of them.

For CVE-2019-9511, also known as Data Dribble, the new option
stream_window_data_threshold can be used to control how little
the DATA frames that Cowboy sends can get.

For CVE-2019-9516, also known as 0-Length Headers Leak, Cowboy
will now simply reject streams containing 0-length header names.

For CVE-2019-9517, also known as Internal Data Buffering, the
backpressure changes were already pretty good at preventing this
issue, but a new option max_connection_buffer_size was added for
even better control over how much memory we are willing to allocate.

For CVE-2019-9512, also known as Ping Flood; CVE-2019-9515, also
known as Settings Flood; CVE-2019-9518, also known as Empty Frame
Flooding; and similar undocumented scenarios, a frame rate limiting
mechanism was added. By default Cowboy will now allow 1000 frames
every 10 seconds. This can be configured via max_received_frame_rate.

For CVE-2019-9514, also known as Reset Flood, another rate limiting
mechanism was added and can be configured via max_reset_stream_rate.
By default Cowboy will do up to 10 stream resets every 10 seconds.

Finally, nothing was done for CVE-2019-9513, also known as Resource
Loop, because Cowboy does not currently implement the HTTP/2
priority mechanism (in parts because these issues were well known
from the start).

Tests were added for all cases except Internal Data Buffering,
which I'm not sure how to test, and Resource Loop, which is not
currently relevant.

1 files changed, 214 insertions, 22 deletions

diff --git a/test/security_SUITE.erl b/test/security_SUITE.erl
index 4d8a68c..684b78a 100644
--- a/test/security_SUITE.erl
+++ b/test/security_SUITE.erl
@@ -30,7 +30,28 @@ all() ->
 	cowboy_test:common_all().
 
 groups() ->
-	cowboy_test:common_groups(ct_helper:all(?MODULE)).
+	Tests = [nc_rand, nc_zero],
+	H1Tests = [slowloris, slowloris_chunks],
+	H2CTests = [
+		http2_data_dribble,
+		http2_empty_frame_flooding_data,
+		http2_empty_frame_flooding_headers_continuation,
+		http2_empty_frame_flooding_push_promise,
+		http2_ping_flood,
+		http2_reset_flood,
+		http2_settings_flood,
+		http2_zero_length_header_leak
+	],
+	[
+		{http, [parallel], Tests ++ H1Tests},
+		{https, [parallel], Tests ++ H1Tests},
+		{h2, [parallel], Tests},
+		{h2c, [parallel], Tests ++ H2CTests},
+		{http_compress, [parallel], Tests ++ H1Tests},
+		{https_compress, [parallel], Tests ++ H1Tests},
+		{h2_compress, [parallel], Tests},
+		{h2c_compress, [parallel], Tests ++ H2CTests}
+	].
 
 init_per_suite(Config) ->
 	ct_helper:create_static_dir(config(priv_dir, Config) ++ "/static"),
@@ -49,11 +70,200 @@ end_per_group(Name, _) ->
 
 init_dispatch(_) ->
 	cowboy_router:compile([{"localhost", [
-		{"/", hello_h, []}
+		{"/", hello_h, []},
+		{"/echo/:key", echo_h, []},
+		{"/resp/:key[/:arg]", resp_h, []}
 	]}]).
 
 %% Tests.
 
+http2_data_dribble(Config) ->
+	doc("Request a very large response then update the window 1 byte at a time. (CVE-2019-9511)"),
+	{ok, Socket} = rfc7540_SUITE:do_handshake(Config),
+	%% Send a GET request for a very large response.
+	{HeadersBlock, _} = cow_hpack:encode([
+		{<<":method">>, <<"GET">>},
+		{<<":scheme">>, <<"http">>},
+		{<<":authority">>, <<"localhost">>}, %% @todo Correct port number.
+		{<<":path">>, <<"/resp/stream_body/loop">>}
+	]),
+	ok = gen_tcp:send(Socket, cow_http2:headers(1, fin, HeadersBlock)),
+	%% Receive a response with a few DATA frames draining the window.
+	{ok, <<SkipLen:24, 1:8, _:8, 1:32>>} = gen_tcp:recv(Socket, 9, 1000),
+	{ok, _} = gen_tcp:recv(Socket, SkipLen, 1000),
+	{ok, <<16384:24, 0:8, 0:8, 1:32, _:16384/unit:8>>} = gen_tcp:recv(Socket, 9 + 16384, 1000),
+	{ok, <<16384:24, 0:8, 0:8, 1:32, _:16384/unit:8>>} = gen_tcp:recv(Socket, 9 + 16384, 1000),
+	{ok, <<16384:24, 0:8, 0:8, 1:32, _:16384/unit:8>>} = gen_tcp:recv(Socket, 9 + 16384, 1000),
+	{ok, <<16383:24, 0:8, 0:8, 1:32, _:16383/unit:8>>} = gen_tcp:recv(Socket, 9 + 16383, 1000),
+	%% Send WINDOW_UPDATE frames with a value of 1. The server should
+	%% not attempt to send data until the window is over a configurable threshold.
+	ok = gen_tcp:send(Socket, [
+		cow_http2:window_update(1),
+		cow_http2:window_update(1, 1)
+	]),
+	{error, timeout} = gen_tcp:recv(Socket, 0, 1000),
+	ok.
+
+http2_empty_frame_flooding_data(Config) ->
+	doc("Confirm that Cowboy detects empty DATA frame flooding. (CVE-2019-9518)"),
+	{ok, Socket} = rfc7540_SUITE:do_handshake(Config),
+	%% Send a POST request followed by many empty DATA frames.
+	{HeadersBlock, _} = cow_hpack:encode([
+		{<<":method">>, <<"POST">>},
+		{<<":scheme">>, <<"http">>},
+		{<<":authority">>, <<"localhost">>}, %% @todo Correct port number.
+		{<<":path">>, <<"/echo/read_body">>}
+	]),
+	ok = gen_tcp:send(Socket, cow_http2:headers(1, nofin, HeadersBlock)),
+	_ = [gen_tcp:send(Socket, cow_http2:data(1, nofin, <<>>)) || _ <- lists:seq(1, 2000)],
+	%% When Cowboy detects a flood it must close the connection.
+	%% We skip WINDOW_UPDATE frames sent when Cowboy starts to read the body.
+	case gen_tcp:recv(Socket, 43, 6000) of
+		{ok, <<_:26/unit:8, _:24, 7:8, _:72, 11:32>>} ->
+			ok;
+		%% We also accept the connection being closed immediately,
+		%% which may happen because we send the GOAWAY right before closing.
+		{error, closed} ->
+			ok
+	end.
+
+http2_empty_frame_flooding_headers_continuation(Config) ->
+	doc("Confirm that Cowboy detects empty HEADERS/CONTINUATION frame flooding. (CVE-2019-9518)"),
+	{ok, Socket} = rfc7540_SUITE:do_handshake(Config),
+	%% Send many empty HEADERS/CONTINUATION frames before the headers.
+	ok = gen_tcp:send(Socket, <<0:24, 1:8, 0:9, 1:31>>),
+	_ = [gen_tcp:send(Socket, <<0:24, 9:8, 0:9, 1:31>>) || _ <- lists:seq(1, 2000)],
+	{HeadersBlock, _} = cow_hpack:encode([
+		{<<":method">>, <<"POST">>},
+		{<<":scheme">>, <<"http">>},
+		{<<":authority">>, <<"localhost">>}, %% @todo Correct port number.
+		{<<":path">>, <<"/">>}
+	]),
+	Len = iolist_size(HeadersBlock),
+	_ = gen_tcp:send(Socket, [<<Len:24, 9:8, 0:5, 1:1, 0:1, 1:1, 0:1, 1:31>>, HeadersBlock]),
+	%% When Cowboy detects a flood it must close the connection.
+	case gen_tcp:recv(Socket, 17, 6000) of
+		{ok, <<_:24, 7:8, _:72, 11:32>>} ->
+			ok;
+		%% We also accept the connection being closed immediately,
+		%% which may happen because we send the GOAWAY right before closing.
+		{error, closed} ->
+			ok
+	end.
+
+http2_empty_frame_flooding_push_promise(Config) ->
+	doc("Confirm that Cowboy detects empty PUSH_PROMISE frame flooding. (CVE-2019-9518)"),
+	{ok, Socket} = rfc7540_SUITE:do_handshake(Config),
+	%% Send a HEADERS frame to which we will attach a PUSH_PROMISE.
+	%% We use nofin in order to keep the stream alive.
+	{HeadersBlock, _} = cow_hpack:encode([
+		{<<":method">>, <<"GET">>},
+		{<<":scheme">>, <<"http">>},
+		{<<":authority">>, <<"localhost">>}, %% @todo Correct port number.
+		{<<":path">>, <<"/">>}
+	]),
+	ok = gen_tcp:send(Socket, cow_http2:headers(1, nofin, HeadersBlock)),
+	%% Send nofin PUSH_PROMISE frame without any data.
+	ok = gen_tcp:send(Socket, <<4:24, 5:8, 0:8, 0:1, 1:31, 0:1, 3:31>>),
+	%% Receive a PROTOCOL_ERROR connection error.
+	%%
+	%% Cowboy rejects all PUSH_PROMISE frames therefore no flooding
+	%% can take place.
+	{ok, <<_:24, 7:8, _:72, 1:32>>} = gen_tcp:recv(Socket, 17, 6000),
+	ok.
+
+%% @todo http2_internal_data_buffering(Config) -> I do not know how to test this.
+%	doc("Request many very large responses, with a larger than necessary window size, "
+%		"but do not attempt to read from the socket. (CVE-2019-9517)"),
+
+http2_ping_flood(Config) ->
+	doc("Confirm that Cowboy detects PING floods. (CVE-2019-9512)"),
+	{ok, Socket} = rfc7540_SUITE:do_handshake(Config),
+	%% Flood the server with PING frames.
+	_ = [gen_tcp:send(Socket, cow_http2:ping(0)) || _ <- lists:seq(1, 2000)],
+	%% Receive a number of PING ACK frames in return, following by the closing of the connection.
+	try
+		[case gen_tcp:recv(Socket, 17, 6000) of
+			{ok, <<8:24, 6:8, _:7, 1:1, _:32, 0:64>>} -> ok;
+			{ok, <<_:24, 7:8, _:72, 11:32>>} -> throw(goaway);
+			%% We also accept the connection being closed immediately,
+			%% which may happen because we send the GOAWAY right before closing.
+			{error, closed} -> throw(goaway)
+		end || _ <- lists:seq(1, 2000)],
+		error(flood_successful)
+	catch throw:goaway ->
+		ok
+	end.
+
+http2_reset_flood(Config) ->
+	doc("Confirm that Cowboy detects reset floods. (CVE-2019-9514)"),
+	{ok, Socket} = rfc7540_SUITE:do_handshake(Config),
+	%% Flood the server with HEADERS frames without a :method pseudo-header.
+	{HeadersBlock, _} = cow_hpack:encode([
+		{<<":scheme">>, <<"http">>},
+		{<<":authority">>, <<"localhost">>}, %% @todo Correct port number.
+		{<<":path">>, <<"/">>}
+	]),
+	_ = [gen_tcp:send(Socket, cow_http2:headers(ID, fin, HeadersBlock)) || ID <- lists:seq(1, 100, 2)],
+	%% Receive a number of RST_STREAM frames in return, following by the closing of the connection.
+	try
+		[case gen_tcp:recv(Socket, 13, 6000) of
+			{ok, <<_:24, 3:8, _:8, ID:32, 1:32>>} -> ok;
+			{ok, <<_:24, 7:8, _:72>>} ->
+				{ok, <<11:32>>} = gen_tcp:recv(Socket, 4, 1000),
+				throw(goaway);
+			%% We also accept the connection being closed immediately,
+			%% which may happen because we send the GOAWAY right before closing.
+			{error, closed} ->
+				throw(goaway)
+		end || ID <- lists:seq(1, 100, 2)],
+		error(flood_successful)
+	catch throw:goaway ->
+		ok
+	end.
+
+%% @todo If we ever implement the PRIORITY mechanism, this test should
+%% be implemented as well. CVE-2019-9513 https://www.kb.cert.org/vuls/id/605641/
+%% http2_resource_loop
+
+http2_settings_flood(Config) ->
+	doc("Confirm that Cowboy detects SETTINGS floods. (CVE-2019-9515)"),
+	{ok, Socket} = rfc7540_SUITE:do_handshake(Config),
+	%% Flood the server with empty SETTINGS frames.
+	_ = [gen_tcp:send(Socket, cow_http2:settings(#{})) || _ <- lists:seq(1, 2000)],
+	%% Receive a number of SETTINGS ACK frames in return, following by the closing of the connection.
+	try
+		[case gen_tcp:recv(Socket, 9, 6000) of
+			{ok, <<0:24, 4:8, 0:7, 1:1, 0:32>>} -> ok;
+			{ok, <<_:24, 7:8, _:40>>} ->
+				{ok, <<_:32, 11:32>>} = gen_tcp:recv(Socket, 8, 1000),
+				throw(goaway);
+			%% We also accept the connection being closed immediately,
+			%% which may happen because we send the GOAWAY right before closing.
+			{error, closed} ->
+				throw(goaway)
+		end || _ <- lists:seq(1, 2000)],
+		error(flood_successful)
+	catch throw:goaway ->
+		ok
+	end.
+
+http2_zero_length_header_leak(Config) ->
+	doc("Confirm that Cowboy rejects HEADERS frame with a 0-length header name. (CVE-2019-9516)"),
+	{ok, Socket} = rfc7540_SUITE:do_handshake(Config),
+	%% Send a GET request with a 0-length header name.
+	{HeadersBlock, _} = cow_hpack:encode([
+		{<<":method">>, <<"GET">>},
+		{<<":scheme">>, <<"http">>},
+		{<<":authority">>, <<"localhost">>}, %% @todo Correct port number.
+		{<<":path">>, <<"/">>},
+		{<<>>, <<"CVE-2019-9516">>}
+	]),
+	ok = gen_tcp:send(Socket, cow_http2:headers(1, fin, HeadersBlock)),
+	%% Receive a PROTOCOL_ERROR stream error.
+	{ok, <<_:24, 3:8, _:8, 1:32, 1:32>>} = gen_tcp:recv(Socket, 13, 6000),
+	ok.
+
 nc_rand(Config) ->
 	doc("Throw random garbage at the server, then check if it's still up."),
 	do_nc(Config, "/dev/urandom").
@@ -67,9 +277,9 @@ do_nc(Config, Input) ->
 	Nc = os:find_executable("nc"),
 	case {Cat, Nc} of
 		{false, _} ->
-			{skip, {not_found, cat}};
+			{skip, "The cat executable was not found."};
 		{_, false} ->
-			{skip, {not_found, nc}};
+			{skip, "The nc executable was not found."};
 		_ ->
 			StrPort = integer_to_list(config(port, Config)),
 			_ = [
@@ -84,15 +294,6 @@ do_nc(Config, Input) ->
 slowloris(Config) ->
 	doc("Send request headers one byte at a time. "
 		"Confirm that the connection gets closed."),
-	_ = case config(protocol, Config) of
-		http ->
-			do_http_slowloris(Config);
-		http2 ->
-			%% @todo Write an equivalent test for HTTP2.
-			ok
-	end.
-
-do_http_slowloris(Config) ->
 	Client = raw_open(Config),
 	try
 		[begin
@@ -107,15 +308,6 @@ do_http_slowloris(Config) ->
 	end.
 
 slowloris_chunks(Config) ->
-	_ = case config(protocol, Config) of
-		http ->
-			do_http_slowloris_chunks(Config);
-		http2 ->
-			%% @todo Write an equivalent test for HTTP2.
-			ok
-	end.
-
-do_http_slowloris_chunks(Config) ->
 	doc("Send request headers one line at a time. "
 		"Confirm that the connection gets closed."),
 	Client = raw_open(Config),