logwrapper/logwrap.c

/*
 * Copyright (C) 2008 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 <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <signal.h>
#include <poll.h>
#include <sys/wait.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <fcntl.h>
#include <libgen.h>
#include <stdbool.h>

#include <logwrap/logwrap.h>
#include "private/android_filesystem_config.h"
#include "cutils/log.h"

#define ARRAY_SIZE(x)	(sizeof(x) / sizeof(*(x)))

static int signal_fd_write;

static void fatal(const char *msg) {
    fprintf(stderr, "%s", msg);
    ALOG(LOG_ERROR, "logwrapper", "%s", msg);
}

static int parent(const char *tag, int parent_read, int signal_fd, pid_t pid,
        int *chld_sts) {
    int status = 0;
    char buffer[4096];
    struct pollfd poll_fds[] = {
        [0] = {
            .fd = signal_fd,
            .events = POLLIN,
        },
        [1] = {
            .fd = parent_read,
            .events = POLLIN,
        },
    };
    int rc = 0;
    sigset_t chldset;

    int a = 0;  // start index of unprocessed data
    int b = 0;  // end index of unprocessed data
    int sz;
    bool remote_hung = false;
    bool found_child = false;

    char *btag = basename(tag);
    if (!btag) btag = (char*) tag;

    sigemptyset(&chldset);
    sigaddset(&chldset, SIGCHLD);
    sigprocmask(SIG_UNBLOCK, &chldset, NULL);

    while (!found_child) {
        if (poll(poll_fds, remote_hung ? 1 : 2, -1) < 0) {
            if (errno == EINTR)
                continue;
            fatal("poll failed\n");
            rc = -1;
            goto err_poll;
        }

        if (!remote_hung) {
            if (poll_fds[1].revents & POLLIN) {
                sz = read(parent_read, &buffer[b], sizeof(buffer) - 1 - b);

                sz += b;
                // Log one line at a time
                for (b = 0; b < sz; b++) {
                    if (buffer[b] == '\r') {
                        buffer[b] = '\0';
                    } else if (buffer[b] == '\n') {
                        buffer[b] = '\0';
                        ALOG(LOG_INFO, btag, "%s", &buffer[a]);
                        a = b + 1;
                    }
                }

                if (a == 0 && b == sizeof(buffer) - 1) {
                    // buffer is full, flush
                    buffer[b] = '\0';
                    ALOG(LOG_INFO, btag, "%s", &buffer[a]);
                    b = 0;
                } else if (a != b) {
                    // Keep left-overs
                    b -= a;
                    memmove(buffer, &buffer[a], b);
                    a = 0;
                } else {
                    a = 0;
                    b = 0;
                }
            }

            if (poll_fds[1].revents & POLLHUP) {
                remote_hung = true;
            }
        }

        if (poll_fds[0].revents & POLLIN) {
            char tmp[32];
            int ret;

            read(signal_fd, tmp, sizeof(tmp));
            while (!found_child) {
                do {
                    ret = waitpid(-1, &status, WNOHANG);
                } while (ret < 0 && errno == EINTR);

                if (ret <= 0)
                    break;

                found_child = (pid == ret);
            }
        }
    }

    // Flush remaining data
    if (a != b) {
        buffer[b] = '\0';
        ALOG(LOG_INFO, btag, "%s", &buffer[a]);
    }

    if (WIFEXITED(status)) {
        if (WEXITSTATUS(status))
            ALOG(LOG_INFO, "logwrapper", "%s terminated by exit(%d)", btag,
                    WEXITSTATUS(status));
    } else if (WIFSIGNALED(status)) {
        ALOG(LOG_INFO, "logwrapper", "%s terminated by signal %d", btag,
                WTERMSIG(status));
    } else if (WIFSTOPPED(status)) {
        ALOG(LOG_INFO, "logwrapper", "%s stopped by signal %d", btag,
                WSTOPSIG(status));
    }
    if (chld_sts != NULL)
        *chld_sts = status;

err_poll:
    return rc;
}

static void child(int argc, char* argv[]) {
    // create null terminated argv_child array
    char* argv_child[argc + 1];
    memcpy(argv_child, argv, argc * sizeof(char *));
    argv_child[argc] = NULL;

    if (execvp(argv_child[0], argv_child)) {
        ALOG(LOG_ERROR, "logwrapper",
            "executing %s failed: %s\n", argv_child[0], strerror(errno));
        exit(-1);
    }
}

void sigchld_handler(int sig) {
    write(signal_fd_write, &sig, 1);
}

int logwrap(int argc, char* argv[], int *status) {
    pid_t pid;
    int parent_ptty;
    int child_ptty;
    char *child_devname = NULL;
    struct sigaction chldact;
    struct sigaction oldchldact;
    sigset_t blockset;
    sigset_t oldset;
    int sockets[2];
    int rc = 0;

    /* Use ptty instead of socketpair so that STDOUT is not buffered */
    parent_ptty = open("/dev/ptmx", O_RDWR);
    if (parent_ptty < 0) {
        fatal("Cannot create parent ptty\n");
        rc = -1;
        goto err_open;
    }

    if (grantpt(parent_ptty) || unlockpt(parent_ptty) ||
            ((child_devname = (char*)ptsname(parent_ptty)) == 0)) {
        fatal("Problem with /dev/ptmx\n");
        rc = -1;
        goto err_ptty;
    }

    sigemptyset(&blockset);
    sigaddset(&blockset, SIGCHLD);
    sigprocmask(SIG_BLOCK, &blockset, &oldset);

    pid = fork();
    if (pid < 0) {
        fatal("Failed to fork\n");
        rc = -1;
        goto err_fork;
    } else if (pid == 0) {
        sigprocmask(SIG_SETMASK, &oldset, NULL);
        close(parent_ptty);

        child_ptty = open(child_devname, O_RDWR);
        if (child_ptty < 0) {
            fatal("Problem with child ptty\n");
            return -1;
        }

        // redirect stdout and stderr
        dup2(child_ptty, 1);
        dup2(child_ptty, 2);
        close(child_ptty);

        child(argc - 1, &argv[1]);
        fatal("This should never happen\n");
        return -1;
    } else {
        memset(&chldact, 0, sizeof(chldact));
        chldact.sa_handler = sigchld_handler;
        chldact.sa_flags = SA_NOCLDSTOP;

        sigaction(SIGCHLD, &chldact, &oldchldact);
        if ((!(oldchldact.sa_flags & SA_SIGINFO) &&
                oldchldact.sa_handler != SIG_DFL &&
                oldchldact.sa_handler != SIG_IGN) ||
                ((oldchldact.sa_flags & SA_SIGINFO) &&
                oldchldact.sa_sigaction != NULL)) {
            ALOG(LOG_WARN, "logwrapper", "logwrap replaced the SIGCHLD "
                    "handler and might cause interaction issues");
        }

        rc = socketpair(AF_UNIX, SOCK_STREAM, 0, sockets);
        if (rc == -1) {
            char msg[40];

            snprintf(msg, sizeof(msg), "socketpair failed: %d\n", errno);

            fatal(msg);
            goto err_socketpair;
        }

        fcntl(sockets[0], F_SETFD, FD_CLOEXEC);
        fcntl(sockets[0], F_SETFL, O_NONBLOCK);
        fcntl(sockets[1], F_SETFD, FD_CLOEXEC);
        fcntl(sockets[1], F_SETFL, O_NONBLOCK);

        signal_fd_write = sockets[0];

        // switch user and group to "log"
        // this may fail if we are not root,
        // but in that case switching user/group is unnecessary
        setgid(AID_LOG);
        setuid(AID_LOG);

        rc = parent(argv[1], parent_ptty, sockets[1], pid, status);
    }

    close(sockets[0]);
    close(sockets[1]);
err_socketpair:
    sigaction(SIGCHLD, &oldchldact, NULL);
err_fork:
    sigprocmask(SIG_SETMASK, &oldset, NULL);
err_ptty:
    close(parent_ptty);
err_open:
    return rc;
}