/*
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* Copyright (C) 2018 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#define LOG_TAG "DnsTlsSocket"
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//#define LOG_NDEBUG 0
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#include "DnsTlsSocket.h"
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#include <arpa/inet.h>
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#include <arpa/nameser.h>
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#include <errno.h>
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#include <linux/tcp.h>
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#include <openssl/err.h>
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#include <openssl/sha.h>
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#include <sys/eventfd.h>
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#include <sys/poll.h>
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#include <algorithm>
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#include "DnsTlsSessionCache.h"
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#include "IDnsTlsSocketObserver.h"
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#include "log/log.h"
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#include "netdutils/SocketOption.h"
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namespace android {
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using netdutils::enableSockopt;
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using netdutils::enableTcpKeepAlives;
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using netdutils::isOk;
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using netdutils::Slice;
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using netdutils::Status;
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namespace net {
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namespace {
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constexpr const char kCaCertDir[] = "/system/etc/security/cacerts";
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constexpr size_t SHA256_SIZE = SHA256_DIGEST_LENGTH;
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int waitForReading(int fd) {
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struct pollfd fds = { .fd = fd, .events = POLLIN };
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const int ret = TEMP_FAILURE_RETRY(poll(&fds, 1, -1));
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return ret;
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}
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int waitForWriting(int fd) {
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struct pollfd fds = { .fd = fd, .events = POLLOUT };
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const int ret = TEMP_FAILURE_RETRY(poll(&fds, 1, -1));
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return ret;
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}
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} // namespace
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Status DnsTlsSocket::tcpConnect() {
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ALOGV("%u connecting TCP socket", mMark);
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int type = SOCK_NONBLOCK | SOCK_CLOEXEC;
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switch (mServer.protocol) {
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case IPPROTO_TCP:
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type |= SOCK_STREAM;
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break;
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default:
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return Status(EPROTONOSUPPORT);
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}
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mSslFd.reset(socket(mServer.ss.ss_family, type, mServer.protocol));
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if (mSslFd.get() == -1) {
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ALOGE("Failed to create socket");
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return Status(errno);
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}
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const socklen_t len = sizeof(mMark);
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if (setsockopt(mSslFd.get(), SOL_SOCKET, SO_MARK, &mMark, len) == -1) {
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ALOGE("Failed to set socket mark");
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mSslFd.reset();
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return Status(errno);
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}
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const Status tfo = enableSockopt(mSslFd.get(), SOL_TCP, TCP_FASTOPEN_CONNECT);
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if (!isOk(tfo) && tfo.code() != ENOPROTOOPT) {
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ALOGI("Failed to enable TFO: %s", tfo.msg().c_str());
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}
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// Send 5 keepalives, 3 seconds apart, after 15 seconds of inactivity.
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enableTcpKeepAlives(mSslFd.get(), 15U, 5U, 3U).ignoreError();
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if (connect(mSslFd.get(), reinterpret_cast<const struct sockaddr *>(&mServer.ss),
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sizeof(mServer.ss)) != 0 &&
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errno != EINPROGRESS) {
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ALOGV("Socket failed to connect");
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mSslFd.reset();
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return Status(errno);
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}
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return netdutils::status::ok;
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}
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bool getSPKIDigest(const X509* cert, std::vector<uint8_t>* out) {
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int spki_len = i2d_X509_PUBKEY(X509_get_X509_PUBKEY(cert), nullptr);
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unsigned char spki[spki_len];
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unsigned char* temp = spki;
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if (spki_len != i2d_X509_PUBKEY(X509_get_X509_PUBKEY(cert), &temp)) {
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ALOGW("SPKI length mismatch");
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return false;
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}
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out->resize(SHA256_SIZE);
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unsigned int digest_len = 0;
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int ret = EVP_Digest(spki, spki_len, out->data(), &digest_len, EVP_sha256(), nullptr);
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if (ret != 1) {
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ALOGW("Server cert digest extraction failed");
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return false;
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}
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if (digest_len != out->size()) {
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ALOGW("Wrong digest length: %d", digest_len);
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return false;
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}
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return true;
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}
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bool DnsTlsSocket::initialize() {
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// This method should only be called once, at the beginning, so locking should be
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// unnecessary. This lock only serves to help catch bugs in code that calls this method.
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std::lock_guard guard(mLock);
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if (mSslCtx) {
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// This is a bug in the caller.
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return false;
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}
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mSslCtx.reset(SSL_CTX_new(TLS_method()));
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if (!mSslCtx) {
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return false;
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}
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// Load system CA certs for hostname verification.
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//
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// For discussion of alternative, sustainable approaches see b/71909242.
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if (SSL_CTX_load_verify_locations(mSslCtx.get(), nullptr, kCaCertDir) != 1) {
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ALOGE("Failed to load CA cert dir: %s", kCaCertDir);
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return false;
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}
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// Enable TLS false start
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SSL_CTX_set_false_start_allowed_without_alpn(mSslCtx.get(), 1);
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SSL_CTX_set_mode(mSslCtx.get(), SSL_MODE_ENABLE_FALSE_START);
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// Enable session cache
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mCache->prepareSslContext(mSslCtx.get());
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// Connect
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Status status = tcpConnect();
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if (!status.ok()) {
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return false;
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}
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mSsl = sslConnect(mSslFd.get());
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if (!mSsl) {
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return false;
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}
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mEventFd.reset(eventfd(0, EFD_NONBLOCK | EFD_CLOEXEC));
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// Start the I/O loop.
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mLoopThread.reset(new std::thread(&DnsTlsSocket::loop, this));
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return true;
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}
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bssl::UniquePtr<SSL> DnsTlsSocket::sslConnect(int fd) {
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if (!mSslCtx) {
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ALOGE("Internal error: context is null in sslConnect");
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return nullptr;
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}
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if (!SSL_CTX_set_min_proto_version(mSslCtx.get(), TLS1_2_VERSION)) {
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ALOGE("Failed to set minimum TLS version");
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return nullptr;
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}
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bssl::UniquePtr<SSL> ssl(SSL_new(mSslCtx.get()));
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// This file descriptor is owned by mSslFd, so don't let libssl close it.
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bssl::UniquePtr<BIO> bio(BIO_new_socket(fd, BIO_NOCLOSE));
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SSL_set_bio(ssl.get(), bio.get(), bio.get());
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bio.release();
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if (!mCache->prepareSsl(ssl.get())) {
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return nullptr;
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}
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if (!mServer.name.empty()) {
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if (SSL_set_tlsext_host_name(ssl.get(), mServer.name.c_str()) != 1) {
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ALOGE("Failed to set SNI to %s", mServer.name.c_str());
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return nullptr;
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}
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X509_VERIFY_PARAM* param = SSL_get0_param(ssl.get());
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if (X509_VERIFY_PARAM_set1_host(param, mServer.name.data(), mServer.name.size()) != 1) {
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ALOGE("Failed to set verify host param to %s", mServer.name.c_str());
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return nullptr;
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}
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// This will cause the handshake to fail if certificate verification fails.
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SSL_set_verify(ssl.get(), SSL_VERIFY_PEER, nullptr);
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}
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bssl::UniquePtr<SSL_SESSION> session = mCache->getSession();
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if (session) {
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ALOGV("Setting session");
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SSL_set_session(ssl.get(), session.get());
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} else {
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ALOGV("No session available");
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}
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for (;;) {
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ALOGV("%u Calling SSL_connect", mMark);
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int ret = SSL_connect(ssl.get());
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ALOGV("%u SSL_connect returned %d", mMark, ret);
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if (ret == 1) break; // SSL handshake complete;
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const int ssl_err = SSL_get_error(ssl.get(), ret);
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switch (ssl_err) {
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case SSL_ERROR_WANT_READ:
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if (waitForReading(fd) != 1) {
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ALOGW("SSL_connect read error: %d", errno);
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return nullptr;
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}
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break;
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case SSL_ERROR_WANT_WRITE:
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if (waitForWriting(fd) != 1) {
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ALOGW("SSL_connect write error");
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return nullptr;
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}
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break;
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default:
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ALOGW("SSL_connect error %d, errno=%d", ssl_err, errno);
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return nullptr;
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}
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}
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// TODO: Call SSL_shutdown before discarding the session if validation fails.
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if (!mServer.fingerprints.empty()) {
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ALOGV("Checking DNS over TLS fingerprint");
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// We only care that the chain is internally self-consistent, not that
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// it chains to a trusted root, so we can ignore some kinds of errors.
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// TODO: Add a CA root verification mode that respects these errors.
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int verify_result = SSL_get_verify_result(ssl.get());
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switch (verify_result) {
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case X509_V_OK:
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case X509_V_ERR_DEPTH_ZERO_SELF_SIGNED_CERT:
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case X509_V_ERR_SELF_SIGNED_CERT_IN_CHAIN:
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case X509_V_ERR_CERT_UNTRUSTED:
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break;
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default:
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ALOGW("Invalid certificate chain, error %d", verify_result);
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return nullptr;
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}
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STACK_OF(X509) *chain = SSL_get_peer_cert_chain(ssl.get());
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if (!chain) {
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ALOGW("Server has null certificate");
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return nullptr;
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}
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// Chain and its contents are owned by ssl, so we don't need to free explicitly.
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bool matched = false;
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for (size_t i = 0; i < sk_X509_num(chain); ++i) {
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// This appears to be O(N^2), but there doesn't seem to be a straightforward
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// way to walk a STACK_OF nondestructively in linear time.
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X509* cert = sk_X509_value(chain, i);
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std::vector<uint8_t> digest;
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if (!getSPKIDigest(cert, &digest)) {
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ALOGE("Digest computation failed");
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return nullptr;
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}
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if (mServer.fingerprints.count(digest) > 0) {
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matched = true;
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break;
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}
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}
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if (!matched) {
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ALOGW("No matching fingerprint");
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return nullptr;
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}
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ALOGV("DNS over TLS fingerprint is correct");
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}
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ALOGV("%u handshake complete", mMark);
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return ssl;
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}
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void DnsTlsSocket::sslDisconnect() {
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if (mSsl) {
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SSL_shutdown(mSsl.get());
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mSsl.reset();
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}
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mSslFd.reset();
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}
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bool DnsTlsSocket::sslWrite(const Slice buffer) {
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ALOGV("%u Writing %zu bytes", mMark, buffer.size());
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for (;;) {
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int ret = SSL_write(mSsl.get(), buffer.base(), buffer.size());
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if (ret == int(buffer.size())) break; // SSL write complete;
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if (ret < 1) {
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const int ssl_err = SSL_get_error(mSsl.get(), ret);
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switch (ssl_err) {
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case SSL_ERROR_WANT_WRITE:
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if (waitForWriting(mSslFd.get()) != 1) {
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ALOGV("SSL_write error");
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return false;
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}
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continue;
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case 0:
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break; // SSL write complete;
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default:
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ALOGV("SSL_write error %d", ssl_err);
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return false;
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}
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}
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}
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ALOGV("%u Wrote %zu bytes", mMark, buffer.size());
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return true;
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}
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void DnsTlsSocket::loop() {
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std::lock_guard guard(mLock);
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std::deque<std::vector<uint8_t>> q;
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const int timeout_msecs = DnsTlsSocket::kIdleTimeout.count() * 1000;
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while (true) {
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// poll() ignores negative fds
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struct pollfd fds[2] = { { .fd = -1 }, { .fd = -1 } };
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enum { SSLFD = 0, EVENTFD = 1 };
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// Always listen for a response from server.
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fds[SSLFD].fd = mSslFd.get();
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fds[SSLFD].events = POLLIN;
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// If we have pending queries, wait for space to write one.
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// Otherwise, listen for new queries.
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// Note: This blocks the destructor until q is empty, i.e. until all pending
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// queries are sent or have failed to send.
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if (!q.empty()) {
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fds[SSLFD].events |= POLLOUT;
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} else {
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fds[EVENTFD].fd = mEventFd.get();
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fds[EVENTFD].events = POLLIN;
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}
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const int s = TEMP_FAILURE_RETRY(poll(fds, std::size(fds), timeout_msecs));
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if (s == 0) {
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ALOGV("Idle timeout");
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break;
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}
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if (s < 0) {
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ALOGV("Poll failed: %d", errno);
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break;
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}
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if (fds[SSLFD].revents & (POLLIN | POLLERR | POLLHUP)) {
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if (!readResponse()) {
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ALOGV("SSL remote close or read error.");
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break;
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}
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}
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if (fds[EVENTFD].revents & (POLLIN | POLLERR)) {
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int64_t num_queries;
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ssize_t res = read(mEventFd.get(), &num_queries, sizeof(num_queries));
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if (res < 0) {
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ALOGW("Error during eventfd read");
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break;
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} else if (res == 0) {
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ALOGW("eventfd closed; disconnecting");
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break;
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} else if (res != sizeof(num_queries)) {
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ALOGE("Int size mismatch: %zd != %zu", res, sizeof(num_queries));
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break;
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} else if (num_queries < 0) {
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ALOGV("Negative eventfd read indicates destructor-initiated shutdown");
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break;
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}
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// Take ownership of all pending queries. (q is always empty here.)
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mQueue.swap(q);
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} else if (fds[SSLFD].revents & POLLOUT) {
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// q cannot be empty here.
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// Sending the entire queue here would risk a TCP flow control deadlock, so
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// we only send a single query on each cycle of this loop.
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// TODO: Coalesce multiple pending queries if there is enough space in the
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// write buffer.
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if (!sendQuery(q.front())) {
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break;
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}
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q.pop_front();
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}
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}
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ALOGV("Disconnecting");
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sslDisconnect();
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ALOGV("Calling onClosed");
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mObserver->onClosed();
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ALOGV("Ending loop");
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}
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DnsTlsSocket::~DnsTlsSocket() {
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ALOGV("Destructor");
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// This will trigger an orderly shutdown in loop().
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requestLoopShutdown();
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{
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// Wait for the orderly shutdown to complete.
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std::lock_guard guard(mLock);
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if (mLoopThread && std::this_thread::get_id() == mLoopThread->get_id()) {
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ALOGE("Violation of re-entrance precondition");
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return;
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}
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}
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if (mLoopThread) {
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ALOGV("Waiting for loop thread to terminate");
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mLoopThread->join();
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mLoopThread.reset();
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}
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ALOGV("Destructor completed");
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}
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bool DnsTlsSocket::query(uint16_t id, const Slice query) {
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// Compose the entire message in a single buffer, so that it can be
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// sent as a single TLS record.
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std::vector<uint8_t> buf(query.size() + 4);
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// Write 2-byte length
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uint16_t len = query.size() + 2; // + 2 for the ID.
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buf[0] = len >> 8;
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buf[1] = len;
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// Write 2-byte ID
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buf[2] = id >> 8;
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buf[3] = id;
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// Copy body
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std::memcpy(buf.data() + 4, query.base(), query.size());
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mQueue.push(std::move(buf));
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// Increment the mEventFd counter by 1.
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return incrementEventFd(1);
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}
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void DnsTlsSocket::requestLoopShutdown() {
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if (mEventFd != -1) {
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// Write a negative number to the eventfd. This triggers an immediate shutdown.
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incrementEventFd(INT64_MIN);
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}
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}
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bool DnsTlsSocket::incrementEventFd(const int64_t count) {
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if (mEventFd == -1) {
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ALOGE("eventfd is not initialized");
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return false;
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}
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ssize_t written = write(mEventFd.get(), &count, sizeof(count));
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if (written != sizeof(count)) {
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ALOGE("Failed to increment eventfd by %" PRId64, count);
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return false;
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}
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return true;
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}
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// Read exactly len bytes into buffer or fail with an SSL error code
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int DnsTlsSocket::sslRead(const Slice buffer, bool wait) {
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size_t remaining = buffer.size();
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while (remaining > 0) {
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int ret = SSL_read(mSsl.get(), buffer.limit() - remaining, remaining);
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if (ret == 0) {
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ALOGW_IF(remaining < buffer.size(), "SSL closed with %zu of %zu bytes remaining",
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remaining, buffer.size());
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return SSL_ERROR_ZERO_RETURN;
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}
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if (ret < 0) {
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const int ssl_err = SSL_get_error(mSsl.get(), ret);
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if (wait && ssl_err == SSL_ERROR_WANT_READ) {
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if (waitForReading(mSslFd.get()) != 1) {
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ALOGV("Poll failed in sslRead: %d", errno);
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return SSL_ERROR_SYSCALL;
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}
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continue;
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} else {
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ALOGV("SSL_read error %d", ssl_err);
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return ssl_err;
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}
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}
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remaining -= ret;
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wait = true; // Once a read is started, try to finish.
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}
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return SSL_ERROR_NONE;
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}
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bool DnsTlsSocket::sendQuery(const std::vector<uint8_t>& buf) {
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if (!sslWrite(netdutils::makeSlice(buf))) {
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return false;
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}
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ALOGV("%u SSL_write complete", mMark);
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return true;
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}
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bool DnsTlsSocket::readResponse() {
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ALOGV("reading response");
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uint8_t responseHeader[2];
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int err = sslRead(Slice(responseHeader, 2), false);
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if (err == SSL_ERROR_WANT_READ) {
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ALOGV("Ignoring spurious wakeup from server");
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return true;
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}
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if (err != SSL_ERROR_NONE) {
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return false;
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}
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// Truncate responses larger than MAX_SIZE. This is safe because a DNS packet is
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// always invalid when truncated, so the response will be treated as an error.
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constexpr uint16_t MAX_SIZE = 8192;
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const uint16_t responseSize = (responseHeader[0] << 8) | responseHeader[1];
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ALOGV("%u Expecting response of size %i", mMark, responseSize);
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std::vector<uint8_t> response(std::min(responseSize, MAX_SIZE));
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if (sslRead(netdutils::makeSlice(response), true) != SSL_ERROR_NONE) {
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ALOGV("%u Failed to read %zu bytes", mMark, response.size());
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return false;
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}
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uint16_t remainingBytes = responseSize - response.size();
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while (remainingBytes > 0) {
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constexpr uint16_t CHUNK_SIZE = 2048;
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std::vector<uint8_t> discard(std::min(remainingBytes, CHUNK_SIZE));
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if (sslRead(netdutils::makeSlice(discard), true) != SSL_ERROR_NONE) {
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ALOGV("%u Failed to discard %zu bytes", mMark, discard.size());
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return false;
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}
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remainingBytes -= discard.size();
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}
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ALOGV("%u SSL_read complete", mMark);
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mObserver->onResponse(std::move(response));
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return true;
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}
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} // end of namespace net
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} // end of namespace android
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