libs/binder/RpcTransportRaw.cpp

/*
 * Copyright (C) 2021 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 "RpcRawTransport"
#include <log/log.h>

#include <poll.h>
#include <stddef.h>

#include <binder/RpcTransportRaw.h>

#include "FdTrigger.h"
#include "RpcState.h"
#include "RpcTransportUtils.h"

namespace android {

namespace {

// Linux kernel supports up to 253 (from SCM_MAX_FD) for unix sockets.
constexpr size_t kMaxFdsPerMsg = 253;

// RpcTransport with TLS disabled.
class RpcTransportRaw : public RpcTransport {
public:
    explicit RpcTransportRaw(android::base::unique_fd socket) : mSocket(std::move(socket)) {}
    status_t pollRead(void) override {
        uint8_t buf;
        ssize_t ret = TEMP_FAILURE_RETRY(
                ::recv(mSocket.get(), &buf, sizeof(buf), MSG_PEEK | MSG_DONTWAIT));
        if (ret < 0) {
            int savedErrno = errno;
            if (savedErrno == EAGAIN || savedErrno == EWOULDBLOCK) {
                return WOULD_BLOCK;
            }

            LOG_RPC_DETAIL("RpcTransport poll(): %s", strerror(savedErrno));
            return -savedErrno;
        } else if (ret == 0) {
            return DEAD_OBJECT;
        }

        return OK;
    }

    status_t interruptableWriteFully(
            FdTrigger* fdTrigger, iovec* iovs, int niovs,
            const std::optional<android::base::function_ref<status_t()>>& altPoll,
            const std::vector<std::variant<base::unique_fd, base::borrowed_fd>>* ancillaryFds)
            override {
        bool sentFds = false;
        auto send = [&](iovec* iovs, int niovs) -> ssize_t {
            if (ancillaryFds != nullptr && !ancillaryFds->empty() && !sentFds) {
                if (ancillaryFds->size() > kMaxFdsPerMsg) {
                    // This shouldn't happen because we check the FD count in RpcState.
                    ALOGE("Saw too many file descriptors in RpcTransportCtxRaw: %zu (max is %zu). "
                          "Aborting session.",
                          ancillaryFds->size(), kMaxFdsPerMsg);
                    errno = EINVAL;
                    return -1;
                }

                // CMSG_DATA is not necessarily aligned, so we copy the FDs into a buffer and then
                // use memcpy.
                int fds[kMaxFdsPerMsg];
                for (size_t i = 0; i < ancillaryFds->size(); i++) {
                    fds[i] = std::visit([](const auto& fd) { return fd.get(); },
                                        ancillaryFds->at(i));
                }
                const size_t fdsByteSize = sizeof(int) * ancillaryFds->size();

                alignas(struct cmsghdr) char msgControlBuf[CMSG_SPACE(sizeof(int) * kMaxFdsPerMsg)];

                msghdr msg{
                        .msg_iov = iovs,
                        .msg_iovlen = static_cast<decltype(msg.msg_iovlen)>(niovs),
                        .msg_control = msgControlBuf,
                        .msg_controllen = sizeof(msgControlBuf),
                };

                cmsghdr* cmsg = CMSG_FIRSTHDR(&msg);
                cmsg->cmsg_level = SOL_SOCKET;
                cmsg->cmsg_type = SCM_RIGHTS;
                cmsg->cmsg_len = CMSG_LEN(fdsByteSize);
                memcpy(CMSG_DATA(cmsg), fds, fdsByteSize);

                msg.msg_controllen = CMSG_SPACE(fdsByteSize);

                ssize_t processedSize = TEMP_FAILURE_RETRY(
                        sendmsg(mSocket.get(), &msg, MSG_NOSIGNAL | MSG_CMSG_CLOEXEC));
                if (processedSize > 0) {
                    sentFds = true;
                }
                return processedSize;
            }

            msghdr msg{
                    .msg_iov = iovs,
                    // posix uses int, glibc uses size_t.  niovs is a
                    // non-negative int and can be cast to either.
                    .msg_iovlen = static_cast<decltype(msg.msg_iovlen)>(niovs),
            };
            return TEMP_FAILURE_RETRY(sendmsg(mSocket.get(), &msg, MSG_NOSIGNAL));
        };
        return interruptableReadOrWrite(mSocket.get(), fdTrigger, iovs, niovs, send, "sendmsg",
                                        POLLOUT, altPoll);
    }

    status_t interruptableReadFully(
            FdTrigger* fdTrigger, iovec* iovs, int niovs,
            const std::optional<android::base::function_ref<status_t()>>& altPoll,
            std::vector<std::variant<base::unique_fd, base::borrowed_fd>>* ancillaryFds) override {
        auto recv = [&](iovec* iovs, int niovs) -> ssize_t {
            if (ancillaryFds != nullptr) {
                int fdBuffer[kMaxFdsPerMsg];
                alignas(struct cmsghdr) char msgControlBuf[CMSG_SPACE(sizeof(fdBuffer))];

                msghdr msg{
                        .msg_iov = iovs,
                        .msg_iovlen = static_cast<decltype(msg.msg_iovlen)>(niovs),
                        .msg_control = msgControlBuf,
                        .msg_controllen = sizeof(msgControlBuf),
                };
                ssize_t processSize =
                        TEMP_FAILURE_RETRY(recvmsg(mSocket.get(), &msg, MSG_NOSIGNAL));
                if (processSize < 0) {
                    return -1;
                }

                for (cmsghdr* cmsg = CMSG_FIRSTHDR(&msg); cmsg != nullptr;
                     cmsg = CMSG_NXTHDR(&msg, cmsg)) {
                    if (cmsg->cmsg_level == SOL_SOCKET && cmsg->cmsg_type == SCM_RIGHTS) {
                        // NOTE: It is tempting to reinterpret_cast, but cmsg(3) explicitly asks
                        // application devs to memcpy the data to ensure memory alignment.
                        size_t dataLen = cmsg->cmsg_len - CMSG_LEN(0);
                        LOG_ALWAYS_FATAL_IF(dataLen > sizeof(fdBuffer)); // sanity check
                        memcpy(fdBuffer, CMSG_DATA(cmsg), dataLen);
                        size_t fdCount = dataLen / sizeof(int);
                        ancillaryFds->reserve(ancillaryFds->size() + fdCount);
                        for (size_t i = 0; i < fdCount; i++) {
                            ancillaryFds->emplace_back(base::unique_fd(fdBuffer[i]));
                        }
                        break;
                    }
                }

                if (msg.msg_flags & MSG_CTRUNC) {
                    ALOGE("msg was truncated. Aborting session.");
                    errno = EPIPE;
                    return -1;
                }

                return processSize;
            }
            msghdr msg{
                    .msg_iov = iovs,
                    // posix uses int, glibc uses size_t.  niovs is a
                    // non-negative int and can be cast to either.
                    .msg_iovlen = static_cast<decltype(msg.msg_iovlen)>(niovs),
            };
            return TEMP_FAILURE_RETRY(recvmsg(mSocket.get(), &msg, MSG_NOSIGNAL));
        };
        return interruptableReadOrWrite(mSocket.get(), fdTrigger, iovs, niovs, recv, "recvmsg",
                                        POLLIN, altPoll);
    }

private:
    base::unique_fd mSocket;
};

// RpcTransportCtx with TLS disabled.
class RpcTransportCtxRaw : public RpcTransportCtx {
public:
    std::unique_ptr<RpcTransport> newTransport(android::base::unique_fd fd, FdTrigger*) const {
        return std::make_unique<RpcTransportRaw>(std::move(fd));
    }
    std::vector<uint8_t> getCertificate(RpcCertificateFormat) const override { return {}; }
};

} // namespace

std::unique_ptr<RpcTransportCtx> RpcTransportCtxFactoryRaw::newServerCtx() const {
    return std::make_unique<RpcTransportCtxRaw>();
}

std::unique_ptr<RpcTransportCtx> RpcTransportCtxFactoryRaw::newClientCtx() const {
    return std::make_unique<RpcTransportCtxRaw>();
}

const char *RpcTransportCtxFactoryRaw::toCString() const {
    return "raw";
}

std::unique_ptr<RpcTransportCtxFactory> RpcTransportCtxFactoryRaw::make() {
    return std::unique_ptr<RpcTransportCtxFactoryRaw>(new RpcTransportCtxFactoryRaw());
}

} // namespace android