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android13/packages/modules/DnsResolver/DnsTlsSocket.cpp

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/*
* Copyright (C) 2018 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#define LOG_TAG "resolv"
#include "DnsTlsSocket.h"
#include <arpa/inet.h>
#include <arpa/nameser.h>
#include <errno.h>
#include <linux/tcp.h>
#include <openssl/err.h>
#include <openssl/sha.h>
#include <sys/eventfd.h>
#include <sys/poll.h>
#include <unistd.h>
#include <algorithm>
#include "DnsTlsSessionCache.h"
#include "IDnsTlsSocketObserver.h"
#include <android-base/logging.h>
#include <netdutils/SocketOption.h>
#include <netdutils/ThreadUtil.h>
#include "Experiments.h"
#include "netd_resolv/resolv.h"
#include "private/android_filesystem_config.h" // AID_DNS
#include "resolv_private.h"
namespace android {
using netdutils::enableSockopt;
using netdutils::enableTcpKeepAlives;
using netdutils::isOk;
using netdutils::setThreadName;
using netdutils::Slice;
using netdutils::Status;
namespace net {
namespace {
constexpr const char kCaCertDir[] = "/system/etc/security/cacerts";
int waitForReading(int fd, int timeoutMs = -1) {
pollfd fds = {.fd = fd, .events = POLLIN};
return TEMP_FAILURE_RETRY(poll(&fds, 1, timeoutMs));
}
int waitForWriting(int fd, int timeoutMs = -1) {
pollfd fds = {.fd = fd, .events = POLLOUT};
return TEMP_FAILURE_RETRY(poll(&fds, 1, timeoutMs));
}
} // namespace
Status DnsTlsSocket::tcpConnect() {
LOG(DEBUG) << mMark << " connecting TCP socket";
int type = SOCK_NONBLOCK | SOCK_CLOEXEC;
switch (mServer.protocol) {
case IPPROTO_TCP:
type |= SOCK_STREAM;
break;
default:
return Status(EPROTONOSUPPORT);
}
mSslFd.reset(socket(mServer.ss.ss_family, type, mServer.protocol));
if (mSslFd.get() == -1) {
PLOG(ERROR) << "Failed to create socket";
return Status(errno);
}
resolv_tag_socket(mSslFd.get(), AID_DNS, NET_CONTEXT_INVALID_PID);
const socklen_t len = sizeof(mMark);
if (setsockopt(mSslFd.get(), SOL_SOCKET, SO_MARK, &mMark, len) == -1) {
const int err = errno;
PLOG(ERROR) << "Failed to set socket mark";
mSslFd.reset();
return Status(err);
}
const Status tfo = enableSockopt(mSslFd.get(), SOL_TCP, TCP_FASTOPEN_CONNECT);
if (!isOk(tfo) && tfo.code() != ENOPROTOOPT) {
LOG(WARNING) << "Failed to enable TFO: " << tfo.msg();
}
// Send 5 keepalives, 3 seconds apart, after 15 seconds of inactivity.
enableTcpKeepAlives(mSslFd.get(), 15U, 5U, 3U).ignoreError();
if (connect(mSslFd.get(), reinterpret_cast<const struct sockaddr *>(&mServer.ss),
sizeof(mServer.ss)) != 0 &&
errno != EINPROGRESS) {
const int err = errno;
PLOG(WARNING) << "Socket failed to connect";
mSslFd.reset();
return Status(err);
}
return netdutils::status::ok;
}
bool DnsTlsSocket::setTestCaCertificate() {
bssl::UniquePtr<BIO> bio(
BIO_new_mem_buf(mServer.certificate.data(), mServer.certificate.size()));
bssl::UniquePtr<X509> cert(PEM_read_bio_X509(bio.get(), nullptr, nullptr, nullptr));
if (!cert) {
LOG(ERROR) << "Failed to read cert";
return false;
}
X509_STORE* cert_store = SSL_CTX_get_cert_store(mSslCtx.get());
if (!X509_STORE_add_cert(cert_store, cert.get())) {
LOG(ERROR) << "Failed to add cert";
return false;
}
return true;
}
// TODO: Try to use static sSslCtx instead of mSslCtx
bool DnsTlsSocket::initialize() {
// This method is called every time when a new SSL connection is created.
// This lock only serves to help catch bugs in code that calls this method.
std::lock_guard guard(mLock);
if (mSslCtx) {
// This is a bug in the caller.
return false;
}
mSslCtx.reset(SSL_CTX_new(TLS_method()));
if (!mSslCtx) {
return false;
}
// Load system CA certs from CAPath for hostname verification.
//
// For discussion of alternative, sustainable approaches see b/71909242.
if (!mServer.certificate.empty()) {
// Inject test CA certs from ResolverParamsParcel.caCertificate for INTERNAL TESTING ONLY.
// This is only allowed by DnsResolverService if the caller is AID_ROOT.
LOG(WARNING) << "Setting test CA certificate. This should never happen in production code.";
if (!setTestCaCertificate()) {
LOG(ERROR) << "Failed to set test CA certificate";
return false;
}
} else {
if (SSL_CTX_load_verify_locations(mSslCtx.get(), nullptr, kCaCertDir) != 1) {
LOG(ERROR) << "Failed to load CA cert dir: " << kCaCertDir;
return false;
}
}
// Enable TLS false start
SSL_CTX_set_false_start_allowed_without_alpn(mSslCtx.get(), 1);
SSL_CTX_set_mode(mSslCtx.get(), SSL_MODE_ENABLE_FALSE_START);
// Enable session cache
mCache->prepareSslContext(mSslCtx.get());
mEventFd.reset(eventfd(0, EFD_NONBLOCK | EFD_CLOEXEC));
mShutdownEvent.reset(eventfd(0, EFD_NONBLOCK | EFD_CLOEXEC));
const Experiments* const instance = Experiments::getInstance();
mConnectTimeoutMs = instance->getFlag("dot_connect_timeout_ms", kDotConnectTimeoutMs);
if (mConnectTimeoutMs < 1000) mConnectTimeoutMs = 1000;
mAsyncHandshake = instance->getFlag("dot_async_handshake", 0);
LOG(DEBUG) << "DnsTlsSocket is initialized with { mConnectTimeoutMs: " << mConnectTimeoutMs
<< ", mAsyncHandshake: " << mAsyncHandshake << " }";
transitionState(State::UNINITIALIZED, State::INITIALIZED);
return true;
}
bool DnsTlsSocket::startHandshake() {
std::lock_guard guard(mLock);
if (mState != State::INITIALIZED) {
LOG(ERROR) << "Calling startHandshake in unexpected state " << static_cast<int>(mState);
return false;
}
transitionState(State::INITIALIZED, State::CONNECTING);
if (!mAsyncHandshake) {
if (Status status = tcpConnect(); !status.ok()) {
transitionState(State::CONNECTING, State::WAIT_FOR_DELETE);
LOG(WARNING) << "TCP Handshake failed: " << status.code();
return false;
}
if (mSsl = sslConnect(mSslFd.get()); !mSsl) {
transitionState(State::CONNECTING, State::WAIT_FOR_DELETE);
LOG(WARNING) << "TLS Handshake failed";
return false;
}
}
// Start the I/O loop.
mLoopThread.reset(new std::thread(&DnsTlsSocket::loop, this));
return true;
}
bssl::UniquePtr<SSL> DnsTlsSocket::prepareForSslConnect(int fd) {
if (!mSslCtx) {
LOG(ERROR) << "Internal error: context is null in sslConnect";
return nullptr;
}
if (!SSL_CTX_set_min_proto_version(mSslCtx.get(), TLS1_2_VERSION)) {
LOG(ERROR) << "Failed to set minimum TLS version";
return nullptr;
}
bssl::UniquePtr<SSL> ssl(SSL_new(mSslCtx.get()));
// This file descriptor is owned by mSslFd, so don't let libssl close it.
bssl::UniquePtr<BIO> bio(BIO_new_socket(fd, BIO_NOCLOSE));
SSL_set_bio(ssl.get(), bio.get(), bio.get());
(void)bio.release();
if (!mCache->prepareSsl(ssl.get())) {
return nullptr;
}
if (!mServer.name.empty()) {
LOG(VERBOSE) << "Checking DNS over TLS hostname = " << mServer.name.c_str();
if (SSL_set_tlsext_host_name(ssl.get(), mServer.name.c_str()) != 1) {
LOG(ERROR) << "Failed to set SNI to " << mServer.name;
return nullptr;
}
X509_VERIFY_PARAM* param = SSL_get0_param(ssl.get());
if (X509_VERIFY_PARAM_set1_host(param, mServer.name.data(), mServer.name.size()) != 1) {
LOG(ERROR) << "Failed to set verify host param to " << mServer.name;
return nullptr;
}
// This will cause the handshake to fail if certificate verification fails.
SSL_set_verify(ssl.get(), SSL_VERIFY_PEER, nullptr);
}
bssl::UniquePtr<SSL_SESSION> session = mCache->getSession();
if (session) {
LOG(DEBUG) << "Setting session";
SSL_set_session(ssl.get(), session.get());
} else {
LOG(DEBUG) << "No session available";
}
return ssl;
}
bssl::UniquePtr<SSL> DnsTlsSocket::sslConnect(int fd) {
bssl::UniquePtr<SSL> ssl;
if (ssl = prepareForSslConnect(fd); !ssl) {
return nullptr;
}
for (;;) {
LOG(DEBUG) << " Calling SSL_connect with mark 0x" << std::hex << mMark;
int ret = SSL_connect(ssl.get());
LOG(DEBUG) << " SSL_connect returned " << ret << " with mark 0x" << std::hex << mMark;
if (ret == 1) break; // SSL handshake complete;
const int ssl_err = SSL_get_error(ssl.get(), ret);
switch (ssl_err) {
case SSL_ERROR_WANT_READ:
// SSL_ERROR_WANT_READ is returned because the application data has been sent during
// the TCP connection handshake, the device is waiting for the SSL handshake reply
// from the server.
if (int err = waitForReading(fd, mConnectTimeoutMs); err <= 0) {
PLOG(WARNING) << "SSL_connect read error " << err << ", mark 0x" << std::hex
<< mMark;
return nullptr;
}
break;
case SSL_ERROR_WANT_WRITE:
// If no application data is sent during the TCP connection handshake, the
// device is waiting for the connection established to perform SSL handshake.
if (int err = waitForWriting(fd, mConnectTimeoutMs); err <= 0) {
PLOG(WARNING) << "SSL_connect write error " << err << ", mark 0x" << std::hex
<< mMark;
return nullptr;
}
break;
default:
PLOG(WARNING) << "SSL_connect ssl error =" << ssl_err << ", mark 0x" << std::hex
<< mMark;
return nullptr;
}
}
LOG(DEBUG) << mMark << " handshake complete";
return ssl;
}
bssl::UniquePtr<SSL> DnsTlsSocket::sslConnectV2(int fd) {
bssl::UniquePtr<SSL> ssl;
if (ssl = prepareForSslConnect(fd); !ssl) {
return nullptr;
}
for (;;) {
LOG(DEBUG) << " Calling SSL_connect with mark 0x" << std::hex << mMark;
int ret = SSL_connect(ssl.get());
LOG(DEBUG) << " SSL_connect returned " << ret << " with mark 0x" << std::hex << mMark;
if (ret == 1) break; // SSL handshake complete;
enum { SSLFD = 0, EVENTFD = 1 };
pollfd fds[2] = {
{.fd = mSslFd.get(), .events = 0},
{.fd = mShutdownEvent.get(), .events = POLLIN},
};
const int ssl_err = SSL_get_error(ssl.get(), ret);
switch (ssl_err) {
case SSL_ERROR_WANT_READ:
fds[SSLFD].events = POLLIN;
break;
case SSL_ERROR_WANT_WRITE:
fds[SSLFD].events = POLLOUT;
break;
default:
PLOG(WARNING) << "SSL_connect ssl error =" << ssl_err << ", mark 0x" << std::hex
<< mMark;
return nullptr;
}
int n = TEMP_FAILURE_RETRY(poll(fds, std::size(fds), mConnectTimeoutMs));
if (n <= 0) {
PLOG(WARNING) << ((n == 0) ? "handshake timeout" : "Poll failed");
return nullptr;
}
if (fds[EVENTFD].revents & (POLLIN | POLLERR)) {
LOG(WARNING) << "Got shutdown request during handshake";
return nullptr;
}
if (fds[SSLFD].revents & POLLERR) {
LOG(WARNING) << "Got POLLERR on SSLFD during handshake";
return nullptr;
}
}
LOG(DEBUG) << mMark << " handshake complete";
return ssl;
}
void DnsTlsSocket::sslDisconnect() {
if (mSsl) {
SSL_shutdown(mSsl.get());
mSsl.reset();
}
mSslFd.reset();
}
bool DnsTlsSocket::sslWrite(const Slice buffer) {
LOG(DEBUG) << mMark << " Writing " << buffer.size() << " bytes";
for (;;) {
int ret = SSL_write(mSsl.get(), buffer.base(), buffer.size());
if (ret == int(buffer.size())) break; // SSL write complete;
if (ret < 1) {
const int ssl_err = SSL_get_error(mSsl.get(), ret);
switch (ssl_err) {
case SSL_ERROR_WANT_WRITE:
if (int err = waitForWriting(mSslFd.get()); err <= 0) {
PLOG(WARNING) << "Poll failed in sslWrite, error " << err;
return false;
}
continue;
case 0:
break; // SSL write complete;
default:
LOG(DEBUG) << "SSL_write error " << ssl_err;
return false;
}
}
}
LOG(DEBUG) << mMark << " Wrote " << buffer.size() << " bytes";
return true;
}
void DnsTlsSocket::loop() {
std::lock_guard guard(mLock);
std::deque<std::vector<uint8_t>> q;
const int timeout_msecs = DnsTlsSocket::kIdleTimeout.count() * 1000;
setThreadName(fmt::format("TlsListen_{}", mMark & 0xffff));
if (mAsyncHandshake) {
if (Status status = tcpConnect(); !status.ok()) {
LOG(WARNING) << "TCP Handshake failed: " << status.code();
mObserver->onClosed();
transitionState(State::CONNECTING, State::WAIT_FOR_DELETE);
return;
}
if (mSsl = sslConnectV2(mSslFd.get()); !mSsl) {
LOG(WARNING) << "TLS Handshake failed";
mObserver->onClosed();
transitionState(State::CONNECTING, State::WAIT_FOR_DELETE);
return;
}
LOG(DEBUG) << "Handshaking succeeded";
}
transitionState(State::CONNECTING, State::CONNECTED);
while (true) {
// poll() ignores negative fds
struct pollfd fds[2] = { { .fd = -1 }, { .fd = -1 } };
enum { SSLFD = 0, EVENTFD = 1 };
// Always listen for a response from server.
fds[SSLFD].fd = mSslFd.get();
fds[SSLFD].events = POLLIN;
// If we have pending queries, wait for space to write one.
// Otherwise, listen for new queries.
// Note: This blocks the destructor until q is empty, i.e. until all pending
// queries are sent or have failed to send.
if (!q.empty()) {
fds[SSLFD].events |= POLLOUT;
} else {
fds[EVENTFD].fd = mEventFd.get();
fds[EVENTFD].events = POLLIN;
}
const int s = TEMP_FAILURE_RETRY(poll(fds, std::size(fds), timeout_msecs));
if (s == 0) {
LOG(DEBUG) << "Idle timeout";
break;
}
if (s < 0) {
PLOG(DEBUG) << "Poll failed";
break;
}
if (fds[SSLFD].revents & (POLLIN | POLLERR | POLLHUP)) {
bool readFailed = false;
// readResponse() only reads one DNS (and consumes exact bytes) from ssl.
// Keep doing so until ssl has no pending data.
// TODO: readResponse() can block until it reads a complete DNS response. Consider
// refactoring it to not get blocked in any case.
do {
if (!readResponse()) {
LOG(DEBUG) << "SSL remote close or read error.";
readFailed = true;
}
} while (SSL_pending(mSsl.get()) > 0 && !readFailed);
if (readFailed) {
break;
}
}
if (fds[EVENTFD].revents & (POLLIN | POLLERR)) {
int64_t num_queries;
ssize_t res = read(mEventFd.get(), &num_queries, sizeof(num_queries));
if (res < 0) {
LOG(WARNING) << "Error during eventfd read";
break;
} else if (res == 0) {
LOG(WARNING) << "eventfd closed; disconnecting";
break;
} else if (res != sizeof(num_queries)) {
LOG(ERROR) << "Int size mismatch: " << res << " != " << sizeof(num_queries);
break;
} else if (num_queries < 0) {
LOG(DEBUG) << "Negative eventfd read indicates destructor-initiated shutdown";
break;
}
// Take ownership of all pending queries. (q is always empty here.)
mQueue.swap(q);
} else if (fds[SSLFD].revents & POLLOUT) {
// q cannot be empty here.
// Sending the entire queue here would risk a TCP flow control deadlock, so
// we only send a single query on each cycle of this loop.
// TODO: Coalesce multiple pending queries if there is enough space in the
// write buffer.
if (!sendQuery(q.front())) {
break;
}
q.pop_front();
}
}
LOG(DEBUG) << "Disconnecting";
sslDisconnect();
LOG(DEBUG) << "Calling onClosed";
mObserver->onClosed();
transitionState(State::CONNECTED, State::WAIT_FOR_DELETE);
LOG(DEBUG) << "Ending loop";
}
DnsTlsSocket::~DnsTlsSocket() {
LOG(DEBUG) << "Destructor";
// This will trigger an orderly shutdown in loop().
requestLoopShutdown();
{
// Wait for the orderly shutdown to complete.
std::lock_guard guard(mLock);
if (mLoopThread && std::this_thread::get_id() == mLoopThread->get_id()) {
LOG(ERROR) << "Violation of re-entrance precondition";
return;
}
}
if (mLoopThread) {
LOG(DEBUG) << "Waiting for loop thread to terminate";
mLoopThread->join();
mLoopThread.reset();
}
LOG(DEBUG) << "Destructor completed";
}
bool DnsTlsSocket::query(uint16_t id, const Slice query) {
// Compose the entire message in a single buffer, so that it can be
// sent as a single TLS record.
std::vector<uint8_t> buf(query.size() + 4);
// Write 2-byte length
uint16_t len = query.size() + 2; // + 2 for the ID.
buf[0] = len >> 8;
buf[1] = len;
// Write 2-byte ID
buf[2] = id >> 8;
buf[3] = id;
// Copy body
std::memcpy(buf.data() + 4, query.base(), query.size());
mQueue.push(std::move(buf));
// Increment the mEventFd counter by 1.
return incrementEventFd(1);
}
void DnsTlsSocket::requestLoopShutdown() {
if (mEventFd != -1) {
// Write a negative number to the eventfd. This triggers an immediate shutdown.
incrementEventFd(INT64_MIN);
}
if (mShutdownEvent != -1) {
if (eventfd_write(mShutdownEvent.get(), INT64_MIN) == -1) {
PLOG(ERROR) << "Failed to write to mShutdownEvent";
}
}
}
bool DnsTlsSocket::incrementEventFd(const int64_t count) {
if (mEventFd == -1) {
LOG(ERROR) << "eventfd is not initialized";
return false;
}
ssize_t written = write(mEventFd.get(), &count, sizeof(count));
if (written != sizeof(count)) {
LOG(ERROR) << "Failed to increment eventfd by " << count;
return false;
}
return true;
}
void DnsTlsSocket::transitionState(State from, State to) {
if (mState != from) {
LOG(WARNING) << "BUG: transitioning from an unexpected state " << static_cast<int>(mState)
<< ", expect: from " << static_cast<int>(from) << " to "
<< static_cast<int>(to);
}
mState = to;
}
// Read exactly len bytes into buffer or fail with an SSL error code
int DnsTlsSocket::sslRead(const Slice buffer, bool wait) {
size_t remaining = buffer.size();
while (remaining > 0) {
int ret = SSL_read(mSsl.get(), buffer.limit() - remaining, remaining);
if (ret == 0) {
if (remaining < buffer.size())
LOG(WARNING) << "SSL closed with " << remaining << " of " << buffer.size()
<< " bytes remaining";
return SSL_ERROR_ZERO_RETURN;
}
if (ret < 0) {
const int ssl_err = SSL_get_error(mSsl.get(), ret);
if (wait && ssl_err == SSL_ERROR_WANT_READ) {
if (int err = waitForReading(mSslFd.get()); err <= 0) {
PLOG(WARNING) << "Poll failed in sslRead, error " << err;
return SSL_ERROR_SYSCALL;
}
continue;
} else {
LOG(DEBUG) << "SSL_read error " << ssl_err;
return ssl_err;
}
}
remaining -= ret;
wait = true; // Once a read is started, try to finish.
}
return SSL_ERROR_NONE;
}
bool DnsTlsSocket::sendQuery(const std::vector<uint8_t>& buf) {
if (!sslWrite(netdutils::makeSlice(buf))) {
return false;
}
LOG(DEBUG) << mMark << " SSL_write complete";
return true;
}
bool DnsTlsSocket::readResponse() {
LOG(DEBUG) << "reading response";
uint8_t responseHeader[2];
int err = sslRead(Slice(responseHeader, 2), false);
if (err == SSL_ERROR_WANT_READ) {
LOG(DEBUG) << "Ignoring spurious wakeup from server";
return true;
}
if (err != SSL_ERROR_NONE) {
return false;
}
// Truncate responses larger than MAX_SIZE. This is safe because a DNS packet is
// always invalid when truncated, so the response will be treated as an error.
constexpr uint16_t MAX_SIZE = 8192;
const uint16_t responseSize = (responseHeader[0] << 8) | responseHeader[1];
LOG(DEBUG) << mMark << " Expecting response of size " << responseSize;
std::vector<uint8_t> response(std::min(responseSize, MAX_SIZE));
if (sslRead(netdutils::makeSlice(response), true) != SSL_ERROR_NONE) {
LOG(DEBUG) << mMark << " Failed to read " << response.size() << " bytes";
return false;
}
uint16_t remainingBytes = responseSize - response.size();
while (remainingBytes > 0) {
constexpr uint16_t CHUNK_SIZE = 2048;
std::vector<uint8_t> discard(std::min(remainingBytes, CHUNK_SIZE));
if (sslRead(netdutils::makeSlice(discard), true) != SSL_ERROR_NONE) {
LOG(DEBUG) << mMark << " Failed to discard " << discard.size() << " bytes";
return false;
}
remainingBytes -= discard.size();
}
LOG(DEBUG) << mMark << " SSL_read complete";
mObserver->onResponse(std::move(response));
return true;
}
} // end of namespace net
} // end of namespace android
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