logd/LogListener.cpp

/*
 * Copyright (C) 2012-2014 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.
 */

#include <ctype.h>
#include <limits.h>
#include <stdio.h>
#include <sys/cdefs.h>
#include <sys/prctl.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <sys/un.h>
#include <unistd.h>

#include <cutils/sockets.h>
#include <private/android_filesystem_config.h>
#include <private/android_logger.h>

#include "LogBuffer.h"
#include "LogListener.h"
#include "LogUtils.h"

LogListener::LogListener(LogBufferInterface* buf, LogReader* reader)
    : SocketListener(getLogSocket(), false), logbuf(buf), reader(reader) {
}

bool LogListener::onDataAvailable(SocketClient* cli) {
    static bool name_set;
    if (!name_set) {
        prctl(PR_SET_NAME, "logd.writer");
        name_set = true;
    }

    // + 1 to ensure null terminator if MAX_PAYLOAD buffer is received
    char buffer[sizeof_log_id_t + sizeof(uint16_t) + sizeof(log_time) +
                LOGGER_ENTRY_MAX_PAYLOAD + 1];
    struct iovec iov = { buffer, sizeof(buffer) - 1 };

    alignas(4) char control[CMSG_SPACE(sizeof(struct ucred))];
    struct msghdr hdr = {
        NULL, 0, &iov, 1, control, sizeof(control), 0,
    };

    int socket = cli->getSocket();

    // To clear the entire buffer is secure/safe, but this contributes to 1.68%
    // overhead under logging load. We are safe because we check counts, but
    // still need to clear null terminator
    // memset(buffer, 0, sizeof(buffer));
    ssize_t n = recvmsg(socket, &hdr, 0);
    if (n <= (ssize_t)(sizeof(android_log_header_t))) {
        return false;
    }

    buffer[n] = 0;

    struct ucred* cred = NULL;

    struct cmsghdr* cmsg = CMSG_FIRSTHDR(&hdr);
    while (cmsg != NULL) {
        if (cmsg->cmsg_level == SOL_SOCKET &&
            cmsg->cmsg_type == SCM_CREDENTIALS) {
            cred = (struct ucred*)CMSG_DATA(cmsg);
            break;
        }
        cmsg = CMSG_NXTHDR(&hdr, cmsg);
    }

    struct ucred fake_cred;
    if (cred == NULL) {
        cred = &fake_cred;
        cred->pid = 0;
        cred->uid = DEFAULT_OVERFLOWUID;
    }

    if (cred->uid == AID_LOGD) {
        // ignore log messages we send to ourself.
        // Such log messages are often generated by libraries we depend on
        // which use standard Android logging.
        return false;
    }

    android_log_header_t* header =
        reinterpret_cast<android_log_header_t*>(buffer);
    log_id_t logId = static_cast<log_id_t>(header->id);
    if (/* logId < LOG_ID_MIN || */ logId >= LOG_ID_MAX ||
        logId == LOG_ID_KERNEL) {
        return false;
    }

    if ((logId == LOG_ID_SECURITY) &&
        (!__android_log_security() ||
         !clientHasLogCredentials(cred->uid, cred->gid, cred->pid))) {
        return false;
    }

    // Check credential validity, acquire corrected details if not supplied.
    if (cred->pid == 0) {
        cred->pid = logbuf ? logbuf->tidToPid(header->tid)
                           : android::tidToPid(header->tid);
        if (cred->pid == getpid()) {
            // We expect that /proc/<tid>/ is accessible to self even without
            // readproc group, so that we will always drop messages that come
            // from any of our logd threads and their library calls.
            return false;  // ignore self
        }
    }
    if (cred->uid == DEFAULT_OVERFLOWUID) {
        uid_t uid =
            logbuf ? logbuf->pidToUid(cred->pid) : android::pidToUid(cred->pid);
        if (uid == AID_LOGD) {
            uid = logbuf ? logbuf->pidToUid(header->tid)
                         : android::pidToUid(cred->pid);
        }
        if (uid != AID_LOGD) cred->uid = uid;
    }

    char* msg = ((char*)buffer) + sizeof(android_log_header_t);
    n -= sizeof(android_log_header_t);

    // NB: hdr.msg_flags & MSG_TRUNC is not tested, silently passing a
    // truncated message to the logs.

    if (logbuf != nullptr) {
        int res = logbuf->log(
            logId, header->realtime, cred->uid, cred->pid, header->tid, msg,
            ((size_t)n <= USHRT_MAX) ? (unsigned short)n : USHRT_MAX);
        if (res > 0 && reader != nullptr) {
            reader->notifyNewLog(static_cast<log_mask_t>(1 << logId));
        }
    }

    return true;
}

int LogListener::getLogSocket() {
    static const char socketName[] = "logdw";
    int sock = android_get_control_socket(socketName);

    if (sock < 0) {  // logd started up in init.sh
        sock = socket_local_server(
            socketName, ANDROID_SOCKET_NAMESPACE_RESERVED, SOCK_DGRAM);

        int on = 1;
        if (setsockopt(sock, SOL_SOCKET, SO_PASSCRED, &on, sizeof(on))) {
            return -1;
        }
    }
    return sock;
}