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Was runing most of the code with real and effective uid of 0, contrary
to the comments.  Fixed that and made sure unlink of job file is done
as root so it can succeed.  Also will now detect empty input.

/*	$OpenBSD: at.c,v 1.3 1996/08/03 20:16:52 millert Exp $	*/
/*	$NetBSD: at.c,v 1.4 1995/03/25 18:13:31 glass Exp $	*/

/*
 * at.c : Put file into atrun queue
 * Copyright (C) 1993  Thomas Koenig
 *
 * Atrun & Atq modifications
 * Copyright (C) 1993  David Parsons
 * All rights reserved.
 *
 * 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 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.
 */

#define _USE_BSD 1

/* System Headers */
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <ctype.h>
#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <pwd.h>
#include <signal.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>

/* Local headers */
#include "at.h"
#include "panic.h"
#include "parsetime.h"
#include "pathnames.h"
#define MAIN
#include "privs.h"

/* Macros */
#define ALARMC 10		/* Number of seconds to wait for timeout */

#define SIZE 255
#define TIMESIZE 50

/* File scope variables */
#ifndef lint
static char rcsid[] = "$OpenBSD: at.c,v 1.3 1996/08/03 20:16:52 millert Exp $";
#endif

char *no_export[] =
{
	"TERM", "TERMCAP", "DISPLAY", "_"
};
static send_mail = 0;

/* External variables */
extern char **environ;
int fcreated;
char *namep;
char atfile[FILENAME_MAX];

char *atinput = (char *) 0;	/* where to get input from */
char atqueue = 0;		/* which queue to examine for jobs (atq) */
char atverify = 0;		/* verify time instead of queuing job */

/* Function declarations */
static void sigc	__P((int signo));
static void alarmc	__P((int signo));
static char *cwdname	__P((void));
static void writefile	__P((time_t runtimer, char queue));
static void list_jobs	__P((void));

/* Signal catching functions */

static void 
sigc(signo)
	int signo;
{
/* If the user presses ^C, remove the spool file and exit
 */
	if (fcreated) {
		PRIV_START
		unlink(atfile);
		PRIV_END
	}

	exit(EXIT_FAILURE);
}

static void 
alarmc(signo)
	int signo;
{
/* Time out after some seconds
 */
	panic("File locking timed out");
}

/* Local functions */

static char *
cwdname()
{
/* Read in the current directory; the name will be overwritten on
 * subsequent calls.
 */
	static char *ptr = NULL;
	static size_t size = SIZE;

	if (ptr == NULL)
		ptr = (char *) malloc(size);

	while (1) {
		if (ptr == NULL)
			panic("Out of memory");

		if (getcwd(ptr, size - 1) != NULL)
			return ptr;

		if (errno != ERANGE)
			perr("Cannot get directory");

		free(ptr);
		size += SIZE;
		ptr = (char *) malloc(size);
	}
}

static void
writefile(runtimer, queue)
	time_t runtimer;
	char queue;
{
	/*
	 * This does most of the work if at or batch are invoked for
	 * writing a job.
	 */
	int i;
	char *ap, *ppos, *mailname;
	struct passwd *pass_entry;
	struct stat statbuf;
	int fdes, lockdes, fd2;
	FILE *fp, *fpin;
	struct sigaction act;
	char **atenv;
	int ch;
	mode_t cmask;
	struct flock lock;

	/*
	 * Install the signal handler for SIGINT; terminate after removing the
	 * spool file if necessary
	 */
	act.sa_handler = sigc;
	sigemptyset(&(act.sa_mask));
	act.sa_flags = 0;

	sigaction(SIGINT, &act, NULL);

	strcpy(atfile, _PATH_ATJOBS);
	ppos = atfile + strlen(_PATH_ATJOBS);

	/*
	 * Loop over all possible file names for running something at this
	 *  particular time, see if a file is there; the first empty slot at
	 *  any particular time is used.  Lock the file _PATH_LOCKFILE first
	 *  to make sure we're alone when doing this.
	 */

	PRIV_START

	if ((lockdes = open(_PATH_LOCKFILE, O_WRONLY | O_CREAT, 0600)) < 0)
		perr2("Cannot open lockfile ", _PATH_LOCKFILE);

	lock.l_type = F_WRLCK;
	lock.l_whence = SEEK_SET;
	lock.l_start = 0;
	lock.l_len = 0;

	act.sa_handler = alarmc;
	sigemptyset(&(act.sa_mask));
	act.sa_flags = 0;

	/*
	 * Set an alarm so a timeout occurs after ALARMC seconds, in case
	 * something is seriously broken.
	 */
	sigaction(SIGALRM, &act, NULL);
	alarm(ALARMC);
	fcntl(lockdes, F_SETLKW, &lock);
	alarm(0);

	for (i = 0; i < AT_MAXJOBS; i++) {
		sprintf(ppos, "%c%8lx.%3x", queue,
		    (unsigned long) (runtimer / 60), i);
		for (ap = ppos; *ap != '\0'; ap++)
			if (*ap == ' ')
				*ap = '0';

		if (stat(atfile, &statbuf) != 0) {
			if (errno == ENOENT)
				break;
			else
				perr2("Cannot access ", _PATH_ATJOBS);
		}
	}			/* for */

	if (i >= AT_MAXJOBS)
		panic("Too many jobs already");

	/*
	 * Create the file. The x bit is only going to be set after it has
	 * been completely written out, to make sure it is not executed in
	 * the meantime.  To make sure they do not get deleted, turn off
	 * their r bit.  Yes, this is a kluge.
	 */
	cmask = umask(S_IRUSR | S_IWUSR | S_IXUSR);
	if ((fdes = creat(atfile, O_WRONLY)) == -1)
		perr("Cannot create atjob file");

	if ((fd2 = dup(fdes)) < 0)
		perr("Error in dup() of job file");

	if (fchown(fd2, real_uid, -1) != 0)
		perr("Cannot give away file");

	PRIV_END

	/*
	 * We've successfully created the file; let's set the flag so it
	 * gets removed in case of an interrupt or error.
	 */
	fcreated = 1;

	/* Now we can release the lock, so other people can access it */
	lock.l_type = F_UNLCK;
	lock.l_whence = SEEK_SET;
	lock.l_start = 0;
	lock.l_len = 0;
	fcntl(lockdes, F_SETLKW, &lock);
	close(lockdes);

	if ((fp = fdopen(fdes, "w")) == NULL)
		panic("Cannot reopen atjob file");

	/*
	 * Get the userid to mail to, first by trying getlogin(), which
	 * reads /etc/utmp, then from LOGNAME, finally from getpwuid().
	 */
	mailname = getlogin();
	if (mailname == NULL)
		mailname = getenv("LOGNAME");

	if ((mailname == NULL) || (mailname[0] == '\0')
	    || (strlen(mailname) > 8)) {
		pass_entry = getpwuid(getuid());
		if (pass_entry != NULL)
			mailname = pass_entry->pw_name;
	}

	if (atinput != (char *) NULL) {
		fpin = freopen(atinput, "r", stdin);
		if (fpin == NULL)
			perr("Cannot open input file");
	}
	fprintf(fp, "#! /bin/sh\n# mail %8s %d\n", mailname, send_mail);

	/* Write out the umask at the time of invocation */
	fprintf(fp, "umask %lo\n", (unsigned long) cmask);

	/*
	 * Write out the environment. Anything that may look like a special
	 * character to the shell is quoted, except for \n, which is done
	 * with a pair of "'s.  Dont't export the no_export list (such as
	 * TERM or DISPLAY) because we don't want these.
	 */
	for (atenv = environ; *atenv != NULL; atenv++) {
		int export = 1;
		char *eqp;

		eqp = strchr(*atenv, '=');
		if (ap == NULL)
			eqp = *atenv;
		else {
			int i;

			for (i = 0;i < sizeof(no_export) /
			    sizeof(no_export[0]); i++) {
				export = export
				    && (strncmp(*atenv, no_export[i],
					(size_t) (eqp - *atenv)) != 0);
			}
			eqp++;
		}

		if (export) {
			fwrite(*atenv, sizeof(char), eqp - *atenv, fp);
			for (ap = eqp; *ap != '\0'; ap++) {
				if (*ap == '\n')
					fprintf(fp, "\"\n\"");
				else {
					if (!isalnum(*ap))
						fputc('\\', fp);

					fputc(*ap, fp);
				}
			}
			fputs("; export ", fp);
			fwrite(*atenv, sizeof(char), eqp - *atenv - 1, fp);
			fputc('\n', fp);

		}
	}
	/*
	 * Cd to the directory at the time and write out all the commands
	 * the user supplies from stdin.
	 */
	fprintf(fp, "cd %s\n", cwdname());

	if ((ch = getchar()) == EOF)
		panic("Input error");

	do {
		fputc(ch, fp);
	} while ((ch = getchar()) != EOF);

	fprintf(fp, "\n");
	if (ferror(fp))
		panic("Output error");

	if (ferror(stdin))
		panic("Input error");

	fclose(fp);

	/*
	 * Set the x bit so that we're ready to start executing
	 */
	if (fchmod(fd2, S_IRUSR | S_IWUSR | S_IXUSR) < 0)
		perr("Cannot give away file");

	close(fd2);
	fprintf(stderr, "Job %s will be executed using /bin/sh\n", ppos);
}

static void
list_jobs()
{
	/*
	 * List all a user's jobs in the queue, by looping through
	 * _PATH_ATJOBS, or everybody's if we are root
	 */
	struct passwd *pw;
	DIR *spool;
	struct dirent *dirent;
	struct stat buf;
	struct tm runtime;
	unsigned long ctm;
	char queue;
	time_t runtimer;
	char timestr[TIMESIZE];
	int first = 1;

	PRIV_START

	    if (chdir(_PATH_ATJOBS) != 0)
		perr2("Cannot change to ", _PATH_ATJOBS);

	if ((spool = opendir(".")) == NULL)
		perr2("Cannot open ", _PATH_ATJOBS);

	/* Loop over every file in the directory */
	while ((dirent = readdir(spool)) != NULL) {
		if (stat(dirent->d_name, &buf) != 0)
			perr2("Cannot stat in ", _PATH_ATJOBS);

		/*
		 * See it's a regular file and has its x bit turned on and
		 * is the user's
		 */
		if (!S_ISREG(buf.st_mode)
		    || ((buf.st_uid != real_uid) && !(real_uid == 0))
		    || !(S_IXUSR & buf.st_mode || atverify))
			continue;

		if (sscanf(dirent->d_name, "%c%8lx", &queue, &ctm) != 2)
			continue;

		if (atqueue && (queue != atqueue))
			continue;

		runtimer = 60 * (time_t) ctm;
		runtime = *localtime(&runtimer);
		strftime(timestr, TIMESIZE, "%X %x", &runtime);
		if (first) {
			printf("Date\t\t\tOwner\tQueue\tJob#\n");
			first = 0;
		}
		pw = getpwuid(buf.st_uid);

		printf("%s\t%s\t%c%s\t%s\n",
		    timestr,
		    pw ? pw->pw_name : "???",
		    queue,
		    (S_IXUSR & buf.st_mode) ? "" : "(done)",
		    dirent->d_name);
	}
	PRIV_END
}

static void
delete_jobs(argc, argv)
	int argc;
	char **argv;
{
	/* Delete every argument (job - ID) given */
	int i;
	struct stat buf;

	PRIV_START

	    if (chdir(_PATH_ATJOBS) != 0)
		perr2("Cannot change to ", _PATH_ATJOBS);

	for (i = optind; i < argc; i++) {
		if (stat(argv[i], &buf) != 0)
			perr(argv[i]);
		if ((buf.st_uid != real_uid) && !(real_uid == 0)) {
			fprintf(stderr, "%s: Not owner\n", argv[i]);
			exit(EXIT_FAILURE);
		}
		if (unlink(argv[i]) != 0)
			perr(argv[i]);
	}
	PRIV_END
}				/* delete_jobs */

/* Global functions */

int
main(argc, argv)
	int argc;
	char **argv;
{
	int c;
	char queue = 'a';
	char *pgm;

	enum {
		ATQ, ATRM, AT, BATCH
	};			/* what program we want to run */
	int program = AT;	/* our default program */
	char *options = "q:f:mv";	/* default options for at */
	time_t timer;

	RELINQUISH_PRIVS

	/* Eat any leading paths */
	if ((pgm = strrchr(argv[0], '/')) == NULL)
		pgm = argv[0];
	else
		pgm++;

	namep = pgm;

	/* find out what this program is supposed to do */
	if (strcmp(pgm, "atq") == 0) {
		program = ATQ;
		options = "q:v";
	} else if (strcmp(pgm, "atrm") == 0) {
		program = ATRM;
		options = "";
	} else if (strcmp(pgm, "batch") == 0) {
		program = BATCH;
		options = "f:mv";
	}

	/* process whatever options we can process */
	opterr = 1;
	while ((c = getopt(argc, argv, options)) != EOF)
		switch (c) {
		case 'v':	/* verify time settings */
			atverify = 1;
			break;

		case 'm':	/* send mail when job is complete */
			send_mail = 1;
			break;

		case 'f':
			atinput = optarg;
			break;

		case 'q':	/* specify queue */
			if (strlen(optarg) > 1)
				usage();

			atqueue = queue = *optarg;
			if ((!islower(queue)) || (queue > 'l'))
				usage();
			break;

		default:
			usage();
			break;
		}
	/* end of options eating */

	/* select our program */
	switch (program) {
	case ATQ:
		list_jobs();
		break;

	case ATRM:
		delete_jobs(argc, argv);
		break;

	case AT:
		timer = parsetime(argc, argv);
		if (atverify) {
			struct tm *tm = localtime(&timer);

			fprintf(stderr, "%s\n", asctime(tm));
		}
		writefile(timer, queue);
		break;

	case BATCH:
		writefile(time(NULL), 'b');
		break;

	default:
		panic("Internal error");
		break;
	}
	exit(EXIT_SUCCESS);
}