liblog/logd_writer.c

/*
 * Copyright (C) 2007-2016 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 <endian.h>
#include <errno.h>
#include <fcntl.h>
#include <inttypes.h>
#include <poll.h>
#include <stdarg.h>
#include <stdatomic.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <time.h>
#include <unistd.h>

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

#include "config_write.h"
#include "log_portability.h"
#include "logger.h"

/* branchless on many architectures. */
#define min(x,y) ((y) ^ (((x) ^ (y)) & -((x) < (y))))

static int logdAvailable(log_id_t LogId);
static int logdOpen();
static void logdClose();
static int logdWrite(log_id_t logId, struct timespec *ts,
                     struct iovec *vec, size_t nr);

LIBLOG_HIDDEN struct android_log_transport_write logdLoggerWrite = {
    .node = { &logdLoggerWrite.node, &logdLoggerWrite.node },
    .context.sock = -EBADF,
    .name = "logd",
    .available = logdAvailable,
    .open = logdOpen,
    .close = logdClose,
    .write = logdWrite,
};

/* log_init_lock assumed */
static int logdOpen()
{
    int i, ret = 0;

    i = atomic_load(&logdLoggerWrite.context.sock);
    if (i < 0) {
        int sock = TEMP_FAILURE_RETRY(socket(PF_UNIX, SOCK_DGRAM |
                                                      SOCK_CLOEXEC |
                                                      SOCK_NONBLOCK, 0));
        if (sock < 0) {
            ret = -errno;
        } else {
            struct sockaddr_un un;
            memset(&un, 0, sizeof(struct sockaddr_un));
            un.sun_family = AF_UNIX;
            strcpy(un.sun_path, "/dev/socket/logdw");

            if (TEMP_FAILURE_RETRY(connect(sock, (struct sockaddr *)&un,
                                           sizeof(struct sockaddr_un))) < 0) {
                ret = -errno;
                switch (ret) {
                case -ENOTCONN:
                case -ECONNREFUSED:
                case -ENOENT:
                    i = atomic_exchange(&logdLoggerWrite.context.sock, ret);
                    /* FALLTHRU */
                default:
                    break;
                }
                close(sock);
            } else {
                ret = atomic_exchange(&logdLoggerWrite.context.sock, sock);
                if ((ret >= 0) && (ret != sock)) {
                    close(ret);
                }
                ret = 0;
            }
        }
    }

    return ret;
}

static void __logdClose(int negative_errno)
{
    int sock = atomic_exchange(&logdLoggerWrite.context.sock, negative_errno);
    if (sock >= 0) {
        close(sock);
    }
}

static void logdClose()
{
    __logdClose(-EBADF);
}

static int logdAvailable(log_id_t logId)
{
    if (logId >= LOG_ID_MAX || logId == LOG_ID_KERNEL) {
        return -EINVAL;
    }
    if (atomic_load(&logdLoggerWrite.context.sock) < 0) {
        if (access("/dev/socket/logdw", W_OK) == 0) {
            return 0;
        }
        return -EBADF;
    }
    return 1;
}

static int logdWrite(log_id_t logId, struct timespec *ts,
                     struct iovec *vec, size_t nr)
{
    ssize_t ret;
    int sock;
    static const unsigned headerLength = 1;
    struct iovec newVec[nr + headerLength];
    android_log_header_t header;
    size_t i, payloadSize;
    static atomic_int_fast32_t dropped;
    static atomic_int_fast32_t droppedSecurity;

    sock = atomic_load(&logdLoggerWrite.context.sock);
    if (sock < 0) switch (sock) {
    case -ENOTCONN:
    case -ECONNREFUSED:
    case -ENOENT:
        break;
    default:
        return -EBADF;
    }

    /* logd, after initialization and priv drop */
    if (__android_log_uid() == AID_LOGD) {
        /*
         * ignore log messages we send to ourself (logd).
         * Such log messages are often generated by libraries we depend on
         * which use standard Android logging.
         */
        return 0;
    }

    /*
     *  struct {
     *      // what we provide to socket
     *      android_log_header_t header;
     *      // caller provides
     *      union {
     *          struct {
     *              char     prio;
     *              char     payload[];
     *          } string;
     *          struct {
     *              uint32_t tag
     *              char     payload[];
     *          } binary;
     *      };
     *  };
     */

    header.tid = gettid();
    header.realtime.tv_sec = ts->tv_sec;
    header.realtime.tv_nsec = ts->tv_nsec;

    newVec[0].iov_base = (unsigned char *)&header;
    newVec[0].iov_len  = sizeof(header);

    if (sock >= 0) {
        int32_t snapshot = atomic_exchange_explicit(&droppedSecurity, 0,
                                                    memory_order_relaxed);
        if (snapshot) {
            android_log_event_int_t buffer;

            header.id = LOG_ID_SECURITY;
            buffer.header.tag = htole32(LIBLOG_LOG_TAG);
            buffer.payload.type = EVENT_TYPE_INT;
            buffer.payload.data = htole32(snapshot);

            newVec[headerLength].iov_base = &buffer;
            newVec[headerLength].iov_len  = sizeof(buffer);

            ret = TEMP_FAILURE_RETRY(writev(sock, newVec, 2));
            if (ret != (ssize_t)(sizeof(header) + sizeof(buffer))) {
                atomic_fetch_add_explicit(&droppedSecurity, snapshot,
                                          memory_order_relaxed);
            }
        }
        snapshot = atomic_exchange_explicit(&dropped, 0, memory_order_relaxed);
        if (snapshot && __android_log_is_loggable_len(ANDROID_LOG_INFO,
                                                      "liblog",
                                                      strlen("liblog"),
                                                      ANDROID_LOG_VERBOSE)) {
            android_log_event_int_t buffer;

            header.id = LOG_ID_EVENTS;
            buffer.header.tag = htole32(LIBLOG_LOG_TAG);
            buffer.payload.type = EVENT_TYPE_INT;
            buffer.payload.data = htole32(snapshot);

            newVec[headerLength].iov_base = &buffer;
            newVec[headerLength].iov_len  = sizeof(buffer);

            ret = TEMP_FAILURE_RETRY(writev(sock, newVec, 2));
            if (ret != (ssize_t)(sizeof(header) + sizeof(buffer))) {
                atomic_fetch_add_explicit(&dropped, snapshot,
                                          memory_order_relaxed);
            }
        }
    }

    header.id = logId;

    for (payloadSize = 0, i = headerLength; i < nr + headerLength; i++) {
        newVec[i].iov_base = vec[i - headerLength].iov_base;
        payloadSize += newVec[i].iov_len = vec[i - headerLength].iov_len;

        if (payloadSize > LOGGER_ENTRY_MAX_PAYLOAD) {
            newVec[i].iov_len -= payloadSize - LOGGER_ENTRY_MAX_PAYLOAD;
            if (newVec[i].iov_len) {
                ++i;
            }
            break;
        }
    }

    /*
     * The write below could be lost, but will never block.
     *
     * ENOTCONN occurs if logd has died.
     * ENOENT occurs if logd is not running and socket is missing.
     * ECONNREFUSED occurs if we can not reconnect to logd.
     * EAGAIN occurs if logd is overloaded.
     */
    if (sock < 0) {
        ret = sock;
    } else {
        ret = TEMP_FAILURE_RETRY(writev(sock, newVec, i));
        if (ret < 0) {
            ret = -errno;
        }
    }
    switch(ret) {
    case -ENOTCONN:
    case -ECONNREFUSED:
    case -ENOENT:
        if (__android_log_trylock()) {
            return ret; /* in a signal handler? try again when less stressed */
        }
        __logdClose(ret);
        ret = logdOpen();
        __android_log_unlock();

        if (ret < 0) {
            return ret;
        }

        ret = TEMP_FAILURE_RETRY(writev(
                atomic_load(&logdLoggerWrite.context.sock), newVec, i));
        if (ret < 0) {
            ret = -errno;
        }
        /* FALLTHRU */
    default:
        break;
    }

    if (ret > (ssize_t)sizeof(header)) {
        ret -= sizeof(header);
    } else if (ret == -EAGAIN) {
        atomic_fetch_add_explicit(&dropped, 1, memory_order_relaxed);
        if (logId == LOG_ID_SECURITY) {
            atomic_fetch_add_explicit(&droppedSecurity, 1,
                                      memory_order_relaxed);
        }
    }

    return ret;
}