| /* |
| * 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 "private/android_filesystem_config.h" // AID_DNS |
| |
| namespace android { |
| |
| using netdutils::enableSockopt; |
| using netdutils::enableTcpKeepAlives; |
| using netdutils::isOk; |
| using netdutils::Slice; |
| using netdutils::Status; |
| |
| namespace net { |
| namespace { |
| |
| constexpr const char kCaCertDir[] = "/system/etc/security/cacerts"; |
| constexpr size_t SHA256_SIZE = SHA256_DIGEST_LENGTH; |
| |
| int waitForReading(int fd) { |
| struct pollfd fds = { .fd = fd, .events = POLLIN }; |
| const int ret = TEMP_FAILURE_RETRY(poll(&fds, 1, -1)); |
| return ret; |
| } |
| |
| int waitForWriting(int fd) { |
| struct pollfd fds = { .fd = fd, .events = POLLOUT }; |
| const int ret = TEMP_FAILURE_RETRY(poll(&fds, 1, -1)); |
| return ret; |
| } |
| |
| } // 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) { |
| LOG(ERROR) << "Failed to create socket"; |
| return Status(errno); |
| } |
| |
| if (fchown(mSslFd.get(), AID_DNS, -1) == -1) { |
| LOG(WARNING) << "Failed to chown socket: %s" << strerror(errno); |
| } |
| |
| const socklen_t len = sizeof(mMark); |
| if (setsockopt(mSslFd.get(), SOL_SOCKET, SO_MARK, &mMark, len) == -1) { |
| LOG(ERROR) << "Failed to set socket mark"; |
| mSslFd.reset(); |
| return Status(errno); |
| } |
| |
| 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) { |
| LOG(DEBUG) << "Socket failed to connect"; |
| mSslFd.reset(); |
| return Status(errno); |
| } |
| |
| return netdutils::status::ok; |
| } |
| |
| bool getSPKIDigest(const X509* cert, std::vector<uint8_t>* out) { |
| int spki_len = i2d_X509_PUBKEY(X509_get_X509_PUBKEY(cert), nullptr); |
| unsigned char spki[spki_len]; |
| unsigned char* temp = spki; |
| if (spki_len != i2d_X509_PUBKEY(X509_get_X509_PUBKEY(cert), &temp)) { |
| LOG(WARNING) << "SPKI length mismatch"; |
| return false; |
| } |
| out->resize(SHA256_SIZE); |
| unsigned int digest_len = 0; |
| int ret = EVP_Digest(spki, spki_len, out->data(), &digest_len, EVP_sha256(), nullptr); |
| if (ret != 1) { |
| LOG(WARNING) << "Server cert digest extraction failed"; |
| return false; |
| } |
| if (digest_len != out->size()) { |
| LOG(WARNING) << "Wrong digest length: " << digest_len; |
| return false; |
| } |
| return true; |
| } |
| |
| bool DnsTlsSocket::initialize() { |
| // This method should only be called once, at the beginning, so locking should be |
| // unnecessary. 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 for hostname verification. |
| // |
| // For discussion of alternative, sustainable approaches see b/71909242. |
| 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()); |
| |
| // Connect |
| Status status = tcpConnect(); |
| if (!status.ok()) { |
| return false; |
| } |
| mSsl = sslConnect(mSslFd.get()); |
| if (!mSsl) { |
| return false; |
| } |
| |
| mEventFd.reset(eventfd(0, EFD_NONBLOCK | EFD_CLOEXEC)); |
| |
| // Start the I/O loop. |
| mLoopThread.reset(new std::thread(&DnsTlsSocket::loop, this)); |
| |
| return true; |
| } |
| |
| bssl::UniquePtr<SSL> DnsTlsSocket::sslConnect(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()); |
| bio.release(); |
| |
| if (!mCache->prepareSsl(ssl.get())) { |
| return nullptr; |
| } |
| |
| if (!mServer.name.empty()) { |
| if (SSL_set_tlsext_host_name(ssl.get(), mServer.name.c_str()) != 1) { |
| LOG(ERROR) << "ailed 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"; |
| } |
| |
| for (;;) { |
| LOG(DEBUG) << mMark << " Calling SSL_connect"; |
| int ret = SSL_connect(ssl.get()); |
| LOG(DEBUG) << mMark << " SSL_connect returned " << ret; |
| 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: |
| if (waitForReading(fd) != 1) { |
| LOG(WARNING) << "SSL_connect read error: " << errno; |
| return nullptr; |
| } |
| break; |
| case SSL_ERROR_WANT_WRITE: |
| if (waitForWriting(fd) != 1) { |
| LOG(WARNING) << "SSL_connect write error"; |
| return nullptr; |
| } |
| break; |
| default: |
| LOG(WARNING) << "SSL_connect error " << ssl_err << ", errno=" << errno; |
| return nullptr; |
| } |
| } |
| |
| // TODO: Call SSL_shutdown before discarding the session if validation fails. |
| if (!mServer.fingerprints.empty()) { |
| LOG(DEBUG) << "Checking DNS over TLS fingerprint"; |
| |
| // We only care that the chain is internally self-consistent, not that |
| // it chains to a trusted root, so we can ignore some kinds of errors. |
| // TODO: Add a CA root verification mode that respects these errors. |
| int verify_result = SSL_get_verify_result(ssl.get()); |
| switch (verify_result) { |
| case X509_V_OK: |
| case X509_V_ERR_DEPTH_ZERO_SELF_SIGNED_CERT: |
| case X509_V_ERR_SELF_SIGNED_CERT_IN_CHAIN: |
| case X509_V_ERR_CERT_UNTRUSTED: |
| break; |
| default: |
| LOG(WARNING) << "Invalid certificate chain, error " << verify_result; |
| return nullptr; |
| } |
| |
| STACK_OF(X509) *chain = SSL_get_peer_cert_chain(ssl.get()); |
| if (!chain) { |
| LOG(WARNING) << "Server has null certificate"; |
| return nullptr; |
| } |
| // Chain and its contents are owned by ssl, so we don't need to free explicitly. |
| bool matched = false; |
| for (size_t i = 0; i < sk_X509_num(chain); ++i) { |
| // This appears to be O(N^2), but there doesn't seem to be a straightforward |
| // way to walk a STACK_OF nondestructively in linear time. |
| X509* cert = sk_X509_value(chain, i); |
| std::vector<uint8_t> digest; |
| if (!getSPKIDigest(cert, &digest)) { |
| LOG(ERROR) << "Digest computation failed"; |
| return nullptr; |
| } |
| |
| if (mServer.fingerprints.count(digest) > 0) { |
| matched = true; |
| break; |
| } |
| } |
| |
| if (!matched) { |
| LOG(WARNING) << "No matching fingerprint"; |
| return nullptr; |
| } |
| |
| LOG(DEBUG) << "DNS over TLS fingerprint is correct"; |
| } |
| |
| 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 (waitForWriting(mSslFd.get()) != 1) { |
| LOG(DEBUG) << "SSL_write error"; |
| 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; |
| 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) { |
| LOG(DEBUG) << "Poll failed: " << errno; |
| break; |
| } |
| if (fds[SSLFD].revents & (POLLIN | POLLERR | POLLHUP)) { |
| if (!readResponse()) { |
| LOG(DEBUG) << "SSL remote close or read error."; |
| 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(); |
| 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); |
| } |
| } |
| |
| 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; |
| } |
| |
| // 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 (waitForReading(mSslFd.get()) != 1) { |
| LOG(DEBUG) << "Poll failed in sslRead: " << errno; |
| 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 |