NetBSD/libexec/atrun/atrun.c

/*	$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;
}