/*      $NetBSD: atrun.c,v 1.23 2017/01/10 20:29:48 christos Exp $      */

/*
 *  atrun.c - run jobs queued by at; run with root privileges.
 *  Copyright (C) 1993, 1994 Thomas Koenig
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. The name of the author(s) may not be used to endorse or promote
 *    products derived from this software without specific prior written
 *    permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR(S) ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR(S) BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/* System Headers */
#include <sys/cdefs.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/wait.h>

#include <ctype.h>
#include <errno.h>
#include <dirent.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <limits.h>
#include <time.h>
#include <unistd.h>
#include <syslog.h>
#include <pwd.h>
#include <grp.h>
#include <err.h>
#include <paths.h>
#include <stdarg.h>

/* Local headers */

#include "privs.h"
#include "pathnames.h"
#include "atrun.h"

/* File scope variables */

#if 0
static char rcsid[] = "$OpenBSD: atrun.c,v 1.7 1997/09/08 22:12:10 millert Exp $";
#else
__RCSID("$NetBSD: atrun.c,v 1.23 2017/01/10 20:29:48 christos Exp $");
#endif

static int debug = 0;

/* Local functions */
static void perr(const char *, ...) __dead;
static void perrx(const char *, ...) __dead;
static int write_string(int, const char *);
static void run_file(const char *, uid_t, gid_t);
static void become_user(struct passwd *, uid_t);

static const char nobody[] = "nobody";

static void
perr(const char *fmt, ...)
{
        char buf[2048];
        va_list ap;

        va_start(ap, fmt);
        (void)vsnprintf(buf, sizeof(buf), fmt, ap);
        va_end(ap);

        if (debug)
                warn("%s", buf);
        else
                syslog(LOG_ERR, "%s: %m", buf);

        exit(EXIT_FAILURE);
}

static void
perrx(const char *fmt, ...)
{
        va_list ap;

        va_start(ap, fmt);

        if (debug)
                vwarnx(fmt, ap);
        else
                vsyslog(LOG_ERR, fmt, ap);

        va_end(ap);

        exit(EXIT_FAILURE);
}

__dead void
privs_fail(const char *msg)
{
        perr("%s", msg);
}

static int
write_string(int fd, const char *a)
{
        return write(fd, a, strlen(a));
}

static void
become_user(struct passwd *pentry, uid_t uid)
{
        if (initgroups(pentry->pw_name, pentry->pw_gid) == -1)
                perr("Cannot init group list for `%s'", pentry->pw_name);

        if (setegid(pentry->pw_gid) == -1 || setgid(pentry->pw_gid) == -1)
                perr("Cannot change primary group to %lu",
                    (unsigned long)pentry->pw_gid);

        if (setsid() == -1)
                perr("Cannot create a session");

        if (setlogin(pentry->pw_name) == -1)
                perr("Cannot set login name to `%s'", pentry->pw_name);

        if (setuid(uid) == -1 || seteuid(uid) == -1)
                perr("Cannot set user id to %lu", (unsigned long)uid);

        if (chdir(pentry->pw_dir) == -1)
                (void)chdir("/");
}

static void
run_file(const char *filename, uid_t uid, gid_t gid)
{
        /*
         * Run a file by by spawning off a process which redirects I/O,
         * spawns a subshell, then waits for it to complete and spawns another
         * process to send mail to the user.
         */
        pid_t pid;
        int fd_out, fd_in;
        int queue;
        char mailbuf[LOGIN_NAME_MAX], fmt[49];
        char *mailname = NULL;
        FILE *stream;
        int send_mail = 0;
        struct stat buf, lbuf;
        off_t size;
        struct passwd *pentry;
        int fflags;
        uid_t nuid;
        gid_t ngid;
        int serrno;

        privs_enter();

        if (chmod(filename, S_IRUSR) == -1)
                perr("Cannot change file permissions to `%s'", filename);

        privs_exit();

        pid = fork();
        if (pid == -1)
                perr("Cannot fork");
        else if (pid != 0)
                return;

        /*
         * Let's see who we mail to.  Hopefully, we can read it from the
         * command file; if not, send it to the owner, or, failing that, to
         * root.
         */

        pentry = getpwuid(uid);
        if (pentry == NULL)
                perrx("Userid %lu not found - aborting job `%s'",
                    (unsigned long)uid, filename);

        privs_enter();

        stream = fopen(filename, "r");
        serrno = errno;

        privs_exit();

        if (stream == NULL) {
                errno = serrno;
                perr("Cannot open input file");
        }

        if (pentry->pw_expire && time(NULL) >= pentry->pw_expire)
                perrx("Userid %lu has expired - aborting job `%s'",
                    (unsigned long)uid, filename);

        if ((fd_in = dup(fileno(stream))) == -1)
                perr("Error duplicating input file descriptor");

        if (fstat(fd_in, &buf) == -1)
                perr("Error in fstat of input file descriptor");

        privs_enter();

        if (lstat(filename, &lbuf) == -1)
                perr("Error in lstat of `%s'", filename);

        privs_exit();

        if (S_ISLNK(lbuf.st_mode))
                perrx("Symbolic link encountered in job `%s' - aborting",
                    filename);

        if ((lbuf.st_dev != buf.st_dev) || (lbuf.st_ino != buf.st_ino) ||
            (lbuf.st_uid != buf.st_uid) || (lbuf.st_gid != buf.st_gid) ||
            (lbuf.st_size!=buf.st_size))
                perrx("Somebody changed files from under us for job `%s' "
                    "- aborting", filename);

        if (buf.st_nlink > 1)
                perrx("Somebody is trying to run a linked script for job `%s'",
                    filename);

        if ((fflags = fcntl(fd_in, F_GETFD)) < 0)
                perr("Error in fcntl");

        (void)fcntl(fd_in, F_SETFD, fflags & ~FD_CLOEXEC);

        (void)snprintf(fmt, sizeof(fmt),
            "#!/bin/sh\n# atrun uid=%%u gid=%%u\n# mail %%%ds %%d",
            LOGIN_NAME_MAX);

        if (fscanf(stream, fmt, &nuid, &ngid, mailbuf, &send_mail) != 4)
                perrx("File `%s' is in wrong format - aborting", filename);

        if (mailbuf[0] == '-')
                perrx("Illegal mail name `%s' in `%s'", mailbuf, filename);

        mailname = mailbuf;
        if (nuid != uid)
                perrx("Job `%s' - userid %lu does not match file uid %lu",
                    filename, (unsigned long)nuid, (unsigned long)uid);

        if (ngid != gid)
                perrx("Job `%s' - groupid %lu does not match file gid %lu",
                    filename, (unsigned long)ngid, (unsigned long)gid);

        (void)fclose(stream);

        privs_enter();

        if (chdir(_PATH_ATSPOOL) == -1)
                perr("Cannot chdir to `%s'", _PATH_ATSPOOL);

        /*
         * Create a file to hold the output of the job we are  about to
         * run. Write the mail header.
         */

        if ((fd_out = open(filename,
                    O_WRONLY | O_CREAT | O_EXCL, S_IWUSR | S_IRUSR)) == -1)
                perr("Cannot create output file `%s'", filename);

        privs_exit();

        write_string(fd_out, "To: ");
        write_string(fd_out, mailname);
        write_string(fd_out, "\nSubject: Output from your job ");
        write_string(fd_out, filename);
        write_string(fd_out, "\n\n");
        if (fstat(fd_out, &buf) == -1)
                perr("Error in fstat of output file descriptor");
        size = buf.st_size;

        (void)close(STDIN_FILENO);
        (void)close(STDOUT_FILENO);
        (void)close(STDERR_FILENO);

        pid = fork();
        if (pid < 0)
                perr("Error in fork");
        else if (pid == 0) {
                char *nul = NULL;
                char **nenvp = &nul;

                /*
                 * Set up things for the child; we want standard input from
                 * the input file, and standard output and error sent to
                 * our output file.
                 */
                if (lseek(fd_in, (off_t) 0, SEEK_SET) == (off_t)-1)
                        perr("Error in lseek");

                if (dup(fd_in) != STDIN_FILENO)
                        perr("Error in I/O redirection");

                if (dup(fd_out) != STDOUT_FILENO)
                        perr("Error in I/O redirection");

                if (dup(fd_out) != STDERR_FILENO)
                        perr("Error in I/O redirection");

                (void)close(fd_in);
                (void)close(fd_out);

                privs_enter();

                if (chdir(_PATH_ATJOBS) == -1)
                        perr("Cannot chdir to `%s'", _PATH_ATJOBS);

                queue = *filename;

                if (queue > 'b')
                    nice(queue - 'b');

                become_user(pentry, uid);

                (void)execle("/bin/sh", "sh", (char *)NULL, nenvp);
                perr("Exec failed for /bin/sh");
        }
        /* We're the parent.  Let's wait. */
        (void)close(fd_in);
        (void)close(fd_out);
        (void)waitpid(pid, NULL, 0);

        /*
         * Send mail.  Unlink the output file first, so it is deleted
         * after the run.
         */
        privs_enter();

        if (stat(filename, &buf) == -1)
                perr("Error in stat of output file `%s'", filename);
        if (open(filename, O_RDONLY) != STDIN_FILENO)
                perr("Open of jobfile `%s' failed", filename);

        (void)unlink(filename);

        privs_exit();

        if ((buf.st_size != size) || send_mail) {
                /* Fork off a child for sending mail */

                privs_enter();

                become_user(pentry, uid);

                execl(_PATH_SENDMAIL, "sendmail", "-F", "Atrun Service",
                    "-odi", "-oem", "-t", (char *) NULL);
                perr("Exec failed for mail command `%s'", _PATH_SENDMAIL);

                privs_exit();
        }
        exit(EXIT_SUCCESS);
}

/* Global functions */

int
main(int argc, char *argv[])
{
        /*
         * Browse through  _PATH_ATJOBS, checking all the jobfiles whether
         * they should be executed and or deleted. The queue is coded into
         * the first byte of the job filename, the date (in minutes since
         * Eon) as a hex number in the following eight bytes, followed by
         * a dot and a serial number.  A file which has not been executed
         * yet is denoted by its execute - bit set.  For those files which
         * are to be executed, run_file() is called, which forks off a
         * child which takes care of I/O redirection, forks off another
         * child for execution and yet another one, optionally, for sending
         * mail.  Files which already have run are removed during the
         * next invocation.
         */
        DIR *spool;
        struct dirent *dirent;
        struct stat buf;
        unsigned long ctm;
        int jobno;
        char queue;
        time_t now, run_time;
        char batch_name[] = "Z2345678901234";
        uid_t batch_uid;
        gid_t batch_gid;
        int c;
        int run_batch;
        double la, load_avg = ATRUN_MAXLOAD;
        struct group *grp;
        struct passwd *pwd;

        openlog("atrun", LOG_PID, LOG_CRON);

        if ((grp = getgrnam(nobody)) == NULL)
                perrx("Cannot get gid for `%s'", nobody);

        if ((pwd = getpwnam(nobody)) == NULL)
                perrx("Cannot get uid for `%s'", nobody);

        /*
         * We don't need root privileges all the time; running under uid
         * and gid nobody is fine except for privileged operations.
         */
        privs_relinquish_root(pwd->pw_uid, grp->gr_gid);

        opterr = 0;
        errno = 0;
        while ((c = getopt(argc, argv, "dl:")) != -1) {
                switch (c) {
                case 'l':
                        if (sscanf(optarg, "%lf", &load_avg) != 1)
                                perrx("Bad argument to option -l: ", optarg);
                        if (load_avg <= 0)
                                load_avg = ATRUN_MAXLOAD;
                        break;

                case 'd':
                        debug++;
                        break;

                case '?':
                        perrx("Usage: %s [-l <loadav>] [-d]", getprogname());
                        /*NOTREACHED*/

                default:
                        perrx("Invalid option: %c", c);
                        /*NOTREACHED*/
                }
        }

        privs_enter();

        if (chdir(_PATH_ATJOBS) == -1)
                perr("Cannot change directory to `%s'", _PATH_ATJOBS);

        /*
         * Main loop. Open spool directory for reading and look over all
         * the files in there. If the filename indicates that the job
         * should be run and the x bit is set, fork off a child which sets
         * its user and group id to that of the files and exec a /bin/sh
         * which executes the shell script. Unlink older files if they
         * should no longer be run.  For deletion, their r bit has to be
         * turned on.
         *
         * Also, pick the oldest batch job to run, at most one per
         * invocation of atrun.
         */
        if ((spool = opendir(".")) == NULL)
                perr("Cannot open `%s'", _PATH_ATJOBS);

        privs_exit();

        now = time(NULL);
        run_batch = 0;
        batch_uid = (uid_t) -1;
        batch_gid = (gid_t) -1;

        while ((dirent = readdir(spool)) != NULL) {
                privs_enter();

                if (stat(dirent->d_name, &buf) == -1)
                        perr("Cannot stat `%s' in `%s'", dirent->d_name,
                            _PATH_ATJOBS);

                privs_exit();

                /* We don't want directories */
                if (!S_ISREG(buf.st_mode))
                        continue;

                if (sscanf(dirent->d_name, "%c%5x%8lx", &queue, &jobno,
                    &ctm) != 3)
                        continue;

                run_time = (time_t) ctm * 60;

                if ((S_IXUSR & buf.st_mode) && (run_time <= now)) {
                        if (isupper((unsigned char)queue) &&
                            (strcmp(batch_name, dirent->d_name) > 0)) {
                                run_batch = 1;
                                (void)strlcpy(batch_name, dirent->d_name,
                                    sizeof(batch_name));
                                batch_uid = buf.st_uid;
                                batch_gid = buf.st_gid;
                        }

                        /* The file is executable and old enough */
                        if (islower((unsigned char)queue))
                                run_file(dirent->d_name, buf.st_uid,
                                    buf.st_gid);
                }

                /* Delete older files */
                if ((run_time < now) && !(S_IXUSR & buf.st_mode) &&
                    (S_IRUSR & buf.st_mode)) {
                        privs_enter();

                        (void)unlink(dirent->d_name);

                        privs_exit();
                }
        }

        /* Run the single batch file, if any */
        if (run_batch && ((getloadavg(&la, 1) == 1) && la < load_avg))
                run_file(batch_name, batch_uid, batch_gid);

        closelog();
        return EXIT_SUCCESS;
}