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http2: do not create ArrayBuffers when no DATA received
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Lazily allocate `ArrayBuffer`s for the contents of DATA frames.
Creating `ArrayBuffer`s is, sadly, not a cheap operation with V8.

This is part of performance improvements to mitigate CVE-2019-9513.

Together with the previous commit, these changes improve throughput
in the adversarial case by about 100 %, and there is little more
that we can do besides artificially limiting the rate of incoming
metadata frames (i.e. after this patch, CPU usage is virtually
exclusively in libnghttp2).

[This backport also applies changes from 83e1b97 and required
some manual work due to the lack of `AllocatedBuffer` on v10.x.
More work was necessary for v8.x, including copying utilities
for `util.h` from more recent Node.js versions.]

Refs: #26201

Backport-PR-URL: #29124
PR-URL: #29122
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
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@addaleax @BethGriggs
addaleax authored and BethGriggs committed Aug 15, 2019
1 parent dd60d35 commit 7de642b
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Showing 4 changed files with 92 additions and 71 deletions.
139 changes: 76 additions & 63 deletions src/node_http2.cc
View file
Expand Up @@ -675,7 +675,7 @@ Http2Session::Http2Session(Environment* env,
ArrayBuffer::New(env->isolate(), js_fields_, kSessionUint8FieldCount);
Local<Uint8Array> uint8_arr =
Uint8Array::New(ab, 0, kSessionUint8FieldCount);
/*USE*/(wrap->Set(env->context(), env->fields_string(), uint8_arr));
USE(wrap->Set(env->context(), env->fields_string(), uint8_arr));
}
}

Expand All @@ -702,6 +702,7 @@ Http2Session::~Http2Session() {
DEBUG_HTTP2SESSION(this, "freeing nghttp2 session");
nghttp2_session_del(session_);
CHECK_EQ(current_nghttp2_memory_, 0);
free(stream_buf_allocation_.base);
}

inline bool HasHttp2Observer(Environment* env) {
Expand Down Expand Up @@ -1211,18 +1212,31 @@ inline int Http2Session::OnDataChunkReceived(nghttp2_session* handle,

stream->statistics_.received_bytes += len;

Local<ArrayBuffer> ab;
if (session->stream_buf_ab_.IsEmpty()) {
ab = ArrayBuffer::New(env->isolate(),
session->stream_buf_allocation_.base,
session->stream_buf_allocation_.len,
v8::ArrayBufferCreationMode::kInternalized);
session->stream_buf_allocation_ = uv_buf_init(nullptr, 0);
session->stream_buf_ab_.Reset(env->isolate(), ab);
} else {
ab = session->stream_buf_ab_.Get(env->isolate());
}

// There is a single large array buffer for the entire data read from the
// network; create a slice of that array buffer and emit it as the
// received data buffer.
CHECK(!session->stream_buf_ab_.IsEmpty());
size_t offset = reinterpret_cast<const char*>(data) - session->stream_buf_;
size_t offset = data - reinterpret_cast<uint8_t*>(session->stream_buf_.base);

// Verify that the data offset is inside the current read buffer.
CHECK_LE(offset, session->stream_buf_size_);
CHECK_LE(offset, session->stream_buf_.len);
CHECK_LE(offset + len, session->stream_buf_.len);

Local<Object> buf =
Buffer::New(env, session->stream_buf_ab_, offset, len).ToLocalChecked();
Local<Object> buffer =
Buffer::New(env, ab, offset, len).ToLocalChecked();

stream->EmitData(len, buf, Local<Object>());
stream->EmitData(len, buffer, Local<Object>());
if (!stream->IsReading())
stream->inbound_consumed_data_while_paused_ += len;
else
Expand Down Expand Up @@ -1841,83 +1855,82 @@ void Http2Session::OnStreamAllocImpl(size_t suggested_size,
uv_buf_t* buf,
void* ctx) {
Http2Session* session = static_cast<Http2Session*>(ctx);
CHECK_EQ(session->stream_buf_, nullptr);
CHECK_EQ(session->stream_buf_size_, 0);
buf->base = session->stream_buf_ = Malloc(suggested_size);
buf->len = session->stream_buf_size_ = suggested_size;
session->IncrementCurrentSessionMemory(suggested_size);
CHECK_EQ(session->stream_buf_.base, nullptr);
CHECK_EQ(session->stream_buf_.len, 0);
*buf = uv_buf_init(Malloc(suggested_size), suggested_size);
}

// Callback used to receive inbound data from the i/o stream
void Http2Session::OnStreamReadImpl(ssize_t nread,
const uv_buf_t* buf,
const uv_buf_t* buf_,
uv_handle_type pending,
void* ctx) {
Http2Session* session = static_cast<Http2Session*>(ctx);
Http2Scope h2scope(session);
CHECK_NE(session->stream_, nullptr);
DEBUG_HTTP2SESSION2(session, "receiving %d bytes", nread);
CHECK_EQ(session->stream_buf_allocation_.base, nullptr);
CHECK(session->stream_buf_ab_.IsEmpty());

// Only pass data on if nread > 0
if (nread <= 0) {
free(session->stream_buf_);
if (buf_ != nullptr)
free(buf_->base);
if (nread < 0) {
uv_buf_t tmp_buf = uv_buf_init(nullptr, 0);
session->prev_read_cb_.fn(nread,
&tmp_buf,
pending,
session->prev_read_cb_.ctx);
}
} else {
// Only pass data on if nread > 0

// Verify that currently: There is memory allocated into which
// the data has been read, and that memory buffer is at least as large
// as the amount of data we have read, but we have not yet made an
// ArrayBuffer out of it.
CHECK_NE(session->stream_buf_, nullptr);
CHECK_EQ(session->stream_buf_, buf->base);
CHECK_EQ(session->stream_buf_size_, buf->len);
CHECK_GE(session->stream_buf_size_, static_cast<size_t>(nread));
CHECK(session->stream_buf_ab_.IsEmpty());
return;
}

Environment* env = session->env();
Isolate* isolate = env->isolate();
HandleScope scope(isolate);
Local<Context> context = env->context();
Context::Scope context_scope(context);
// Shrink to the actual amount of used data.
uv_buf_t buf = *buf_;
buf.base = Realloc(buf.base, nread);

session->IncrementCurrentSessionMemory(nread);
OnScopeLeave on_scope_leave([&]() {
// Once finished handling this write, reset the stream buffer.
// The memory has either been free()d or was handed over to V8.
// We use `nread` instead of `buf.size()` here, because the buffer is
// cleared as part of the `.ToArrayBuffer()` call below.
session->DecrementCurrentSessionMemory(nread);
session->stream_buf_ab_.Reset();
free(session->stream_buf_allocation_.base);
session->stream_buf_allocation_ = uv_buf_init(nullptr, 0);
session->stream_buf_ = uv_buf_init(nullptr, 0);
});

// Create an array buffer for the read data. DATA frames will be emitted
// as slices of this array buffer to avoid having to copy memory.
session->stream_buf_ab_ =
ArrayBuffer::New(isolate,
session->stream_buf_,
session->stream_buf_size_,
v8::ArrayBufferCreationMode::kInternalized);

uv_buf_t buf_ = uv_buf_init(buf->base, nread);
session->statistics_.data_received += nread;
ssize_t ret = session->Write(&buf_, 1);

// Note: if ssize_t is not defined (e.g. on Win32), nghttp2 will typedef
// ssize_t to int. Cast here so that the < 0 check actually works on
// Windows.
if (static_cast<int>(ret) < 0) {
DEBUG_HTTP2SESSION2(session, "fatal error receiving data: %d", ret);

Local<Value> argv[1] = {
Integer::New(isolate, ret),
};
session->MakeCallback(env->error_string(), arraysize(argv), argv);
} else {
session->MaybeStopReading();
}
}
// Make sure that there was no read previously active.
CHECK_EQ(session->stream_buf_.base, nullptr);
CHECK_EQ(session->stream_buf_.len, 0);

// Remember the current buffer, so that OnDataChunkReceived knows the
// offset of a DATA frame's data into the socket read buffer.
session->stream_buf_ = uv_buf_init(buf.base, nread);

// Since we are finished handling this write, reset the stream buffer.
// The memory has either been free()d or was handed over to V8.
session->DecrementCurrentSessionMemory(session->stream_buf_size_);
session->stream_buf_ = nullptr;
session->stream_buf_size_ = 0;
session->stream_buf_ab_ = Local<ArrayBuffer>();
// Verify that currently: There is memory allocated into which
// the data has been read, and that memory buffer is at least as large
// as the amount of data we have read, but we have not yet made an
// ArrayBuffer out of it.
CHECK_LE(static_cast<size_t>(nread), session->stream_buf_.len);

// Store this so we can create an ArrayBuffer for read data from it.
// DATA frames will be emitted as slices of that ArrayBuffer to avoid having
// to copy memory.
session->stream_buf_allocation_ = buf;

session->statistics_.data_received += nread;
ssize_t ret = session->Write(&session->stream_buf_, 1);

if (UNLIKELY(ret < 0)) {
DEBUG_HTTP2SESSION2(session, "fatal error receiving data: %d", ret);
Local<Value> arg = Integer::New(session->env()->isolate(), ret);
session->MakeCallback(session->env()->error_string(), 1, &arg);
return;
}
}

void Http2Session::OnStreamDestructImpl(void* ctx) {
Expand Down
10 changes: 3 additions & 7 deletions src/node_http2.h
View file
Expand Up @@ -834,10 +834,6 @@ class Http2Session : public AsyncWrap {

size_t self_size() const override { return sizeof(*this); }

char* stream_alloc() {
return stream_buf_;
}

// Schedule an RstStream for after the current write finishes.
inline void AddPendingRstStream(int32_t stream_id) {
pending_rst_streams_.emplace_back(stream_id);
Expand Down Expand Up @@ -1062,9 +1058,9 @@ class Http2Session : public AsyncWrap {
// use this to allow timeout tracking during long-lasting writes
uint32_t chunks_sent_since_last_write_ = 0;

char* stream_buf_ = nullptr;
size_t stream_buf_size_ = 0;
v8::Local<v8::ArrayBuffer> stream_buf_ab_;
uv_buf_t stream_buf_ = uv_buf_init(nullptr, 0);
v8::Global<v8::ArrayBuffer> stream_buf_ab_;
uv_buf_t stream_buf_allocation_ = uv_buf_init(nullptr, 0);

size_t max_outstanding_pings_ = DEFAULT_MAX_PINGS;
std::queue<Http2Ping*> outstanding_pings_;
Expand Down
12 changes: 12 additions & 0 deletions src/util.h
View file
Expand Up @@ -33,6 +33,7 @@
#include <stdlib.h>
#include <string.h>

#include <functional>
#include <type_traits> // std::remove_reference

namespace node {
Expand Down Expand Up @@ -433,6 +434,17 @@ class BufferValue : public MaybeStackBuffer<char> {
if (name##_length > 0) \
CHECK_NE(name##_data, nullptr);

// Use this when a variable or parameter is unused in order to explicitly
// silence a compiler warning about that.
template <typename T> inline void USE(T&&) {}

// Run a function when exiting the current scope.
struct OnScopeLeave {
std::function<void()> fn_;

explicit OnScopeLeave(std::function<void()> fn) : fn_(fn) {}
~OnScopeLeave() { fn_(); }
};

} // namespace node

Expand Down
2 changes: 1 addition & 1 deletion test/sequential/test-http2-max-session-memory.js
View file
Expand Up @@ -8,7 +8,7 @@ const http2 = require('http2');

// Test that maxSessionMemory Caps work

const largeBuffer = Buffer.alloc(1e6);
const largeBuffer = Buffer.alloc(2e6);

const server = http2.createServer({ maxSessionMemory: 1 });

Expand Down

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