logd/main.cpp

/*
 * Copyright (C) 2012-2013 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 <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <sched.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/capability.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>

#include <linux/prctl.h>

#include <cutils/properties.h>

#include "private/android_filesystem_config.h"
#include "CommandListener.h"
#include "LogBuffer.h"
#include "LogListener.h"
#include "LogAudit.h"

//
//  The service is designed to be run by init, it does not respond well
// to starting up manually. When starting up manually the sockets will
// fail to open typically for one of the following reasons:
//     EADDRINUSE if logger is running.
//     EACCESS if started without precautions (below)
//
// Here is a cookbook procedure for starting up logd manually assuming
// init is out of the way, pedantically all permissions and selinux
// security is put back in place:
//
//    setenforce 0
//    rm /dev/socket/logd*
//    chmod 777 /dev/socket
//        # here is where you would attach the debugger or valgrind for example
//    runcon u:r:logd:s0 /system/bin/logd </dev/null >/dev/null 2>&1 &
//    sleep 1
//    chmod 755 /dev/socket
//    chown logd.logd /dev/socket/logd*
//    restorecon /dev/socket/logd*
//    setenforce 1
//
// If minimalism prevails, typical for debugging and security is not a concern:
//
//    setenforce 0
//    chmod 777 /dev/socket
//    logd
//

static int drop_privs() {
    struct sched_param param;
    memset(&param, 0, sizeof(param));

    if (sched_setscheduler((pid_t) 0, SCHED_BATCH, &param) < 0) {
        return -1;
    }

    if (prctl(PR_SET_KEEPCAPS, 1) < 0) {
        return -1;
    }

    if (setgid(AID_LOGD) != 0) {
        return -1;
    }

    if (setuid(AID_LOGD) != 0) {
        return -1;
    }

    struct __user_cap_header_struct capheader;
    struct __user_cap_data_struct capdata[2];
    memset(&capheader, 0, sizeof(capheader));
    memset(&capdata, 0, sizeof(capdata));
    capheader.version = _LINUX_CAPABILITY_VERSION_3;
    capheader.pid = 0;

    capdata[CAP_TO_INDEX(CAP_SYSLOG)].permitted = CAP_TO_MASK(CAP_SYSLOG);
    capdata[CAP_TO_INDEX(CAP_AUDIT_CONTROL)].permitted |= CAP_TO_MASK(CAP_AUDIT_CONTROL);

    capdata[0].effective = capdata[0].permitted;
    capdata[1].effective = capdata[1].permitted;
    capdata[0].inheritable = 0;
    capdata[1].inheritable = 0;

    if (capset(&capheader, &capdata[0]) < 0) {
        return -1;
    }

    return 0;
}

// Foreground waits for exit of the three main persistent threads that
// are started here.  The three threads are created to manage UNIX
// domain client sockets for writing, reading and controlling the user
// space logger.  Additional transitory per-client threads are created
// for each reader once they register.
int main() {
    int fdDmesg = -1;
    char dmesg[PROPERTY_VALUE_MAX];
    property_get("logd.auditd.dmesg", dmesg, "1");
    if (atol(dmesg)) {
        fdDmesg = open("/dev/kmsg", O_WRONLY);
    }

    if (drop_privs() != 0) {
        return -1;
    }

    // Serves the purpose of managing the last logs times read on a
    // socket connection, and as a reader lock on a range of log
    // entries.

    LastLogTimes *times = new LastLogTimes();

    // LogBuffer is the object which is responsible for holding all
    // log entries.

    LogBuffer *logBuf = new LogBuffer(times);

    char dgram_qlen_statistics[PROPERTY_VALUE_MAX];
    property_get("logd.dgram_qlen.statistics", dgram_qlen_statistics, "");
    if (atol(dgram_qlen_statistics)) {
        logBuf->enableDgramQlenStatistics();
    }

    // LogReader listens on /dev/socket/logdr. When a client
    // connects, log entries in the LogBuffer are written to the client.

    LogReader *reader = new LogReader(logBuf);
    if (reader->startListener()) {
        exit(1);
    }

    // LogListener listens on /dev/socket/logdw for client
    // initiated log messages. New log entries are added to LogBuffer
    // and LogReader is notified to send updates to connected clients.

    LogListener *swl = new LogListener(logBuf, reader);
    // Backlog and /proc/sys/net/unix/max_dgram_qlen set to large value
    if (swl->startListener(300)) {
        exit(1);
    }

    // Command listener listens on /dev/socket/logd for incoming logd
    // administrative commands.

    CommandListener *cl = new CommandListener(logBuf, reader, swl);
    if (cl->startListener()) {
        exit(1);
    }

    // LogAudit listens on NETLINK_AUDIT socket for selinux
    // initiated log messages. New log entries are added to LogBuffer
    // and LogReader is notified to send updates to connected clients.

    // failure is an option ... messages are in dmesg (required by standard)
    LogAudit *al = new LogAudit(logBuf, reader, fdDmesg);
    if (al->startListener()) {
        delete al;
        close(fdDmesg);
    }

    pause();
    exit(0);
}