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Add an acct(5) flag for pledge violations.  Then lastcomm(1) shows
when something went wrong.  This allows to monitor whether the
system is under attack and that the attack has been prevented by
OpenBSD pledge(2).
OK deraadt@ millert@ jmc@

/*	$OpenBSD: lastcomm.c,v 1.25 2017/06/07 20:53:59 bluhm Exp $	*/
/*	$NetBSD: lastcomm.c,v 1.9 1995/10/22 01:43:42 ghudson Exp $	*/

/*
 * Copyright (c) 1980, 1993
 *	The Regents of the University of California.  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. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``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 REGENTS OR CONTRIBUTORS 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, WHETHER 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.
 */

#include <sys/param.h>	/* NODEV */
#include <sys/stat.h>
#include <sys/acct.h>

#include <ctype.h>
#include <err.h>
#include <fcntl.h>
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <utmp.h>
#include <pwd.h>
#include "pathnames.h"

time_t	 expand(u_int);
char	*flagbits(int);
char	*getdev(dev_t);
int	 requested(char *[], struct acct *);
void	 usage(void);

#define SECSPERMIN	(60)
#define SECSPERHOUR	(60 * 60)

int
main(int argc, char *argv[])
{
	char *p;
	struct acct ab;
	struct stat sb;
	FILE *fp;
	off_t size;
	time_t t;
	double delta;
	int ch;
	char *acctfile;

	if (pledge("stdio rpath getpw", NULL) == -1)
		err(1, "pledge");

	acctfile = _PATH_ACCT;
	while ((ch = getopt(argc, argv, "f:")) != -1)
		switch(ch) {
		case 'f':
			acctfile = optarg;
			break;
		case '?':
		default:
			usage();
		}
	argc -= optind;
	argv += optind;

	/* Open the file. */
	if ((fp = fopen(acctfile, "r")) == NULL || fstat(fileno(fp), &sb))
		err(1, "%s", acctfile);

	/*
	 * Round off to integral number of accounting records, probably
	 * not necessary, but it doesn't hurt.
	 */
	size = sb.st_size - sb.st_size % sizeof(struct acct);

	/* Check if any records to display. */
	if (size < sizeof(struct acct))
		exit(0);

	/*
	 * Seek to before the last entry in the file; use lseek(2) in case
	 * the file is bigger than a "long".
	 */
	size -= sizeof(struct acct);
	if (lseek(fileno(fp), size, SEEK_SET) == -1)
		err(1, "%s", acctfile);

	for (;;) {
		if (fread(&ab, sizeof(struct acct), 1, fp) != 1)
			err(1, "%s", acctfile);

		if (ab.ac_comm[0] == '\0') {
			ab.ac_comm[0] = '?';
			ab.ac_comm[1] = '\0';
		} else
			for (p = &ab.ac_comm[0];
			    p < &ab.ac_comm[sizeof ab.ac_comm] && *p; ++p)
				if (!isprint((unsigned char)*p))
					*p = '?';
		if (!*argv || requested(argv, &ab))
		{
			t = expand(ab.ac_utime) + expand(ab.ac_stime);
			(void)printf("%-*.*s %-7s %-*.*s %-*.*s %6.2f secs %.16s",
			    (int)sizeof ab.ac_comm,
			    (int)sizeof ab.ac_comm,
			    ab.ac_comm, flagbits(ab.ac_flag), UT_NAMESIZE,
			    UT_NAMESIZE, user_from_uid(ab.ac_uid, 0),
			    UT_LINESIZE, UT_LINESIZE, getdev(ab.ac_tty),
			    t / (double)AHZ, ctime(&ab.ac_btime));
			delta = expand(ab.ac_etime) / (double)AHZ;
			printf(" (%1.0f:%02.0f:%05.2f)\n",
			    delta / SECSPERHOUR,
			    fmod(delta, (double)SECSPERHOUR) / SECSPERMIN,
			    fmod(delta, (double)SECSPERMIN));
		}

		if (size == 0)
			break;
		/* seek to previous entry */
		if (fseek(fp, 2 * -(long)sizeof(struct acct), SEEK_CUR) == -1)
			err(1, "%s", acctfile);
		size -= sizeof(struct acct);
	}
	exit(0);
}

time_t
expand(u_int t)
{
	time_t nt;

	nt = t & 017777;
	t >>= 13;
	while (t) {
		t--;
		nt <<= 3;
	}
	return (nt);
}

char *
flagbits(int f)
{
	static char flags[20] = "-";
	char *p;

#define	BIT(flag, ch)	if (f & flag) *p++ = ch

	p = flags + 1;
	BIT(ASU, 'S');
	BIT(AFORK, 'F');
	BIT(ACOMPAT, 'C');
	BIT(ACORE, 'D');
	BIT(AXSIG, 'X');
	BIT(APLEDGE, 'P');
	*p = '\0';
	return (flags);
}

int
requested(char *argv[], struct acct *acp)
{
	do {
		if (!strcmp(user_from_uid(acp->ac_uid, 0), *argv))
			return (1);
		if (!strcmp(getdev(acp->ac_tty), *argv))
			return (1);
		if (!strncmp(acp->ac_comm, *argv, sizeof acp->ac_comm))
			return (1);
	} while (*++argv);
	return (0);
}

char *
getdev(dev_t dev)
{
	static dev_t lastdev = (dev_t)-1;
	static char *lastname;

	if (dev == NODEV)			/* Special case. */
		return ("__");
	if (dev == lastdev)			/* One-element cache. */
		return (lastname);
	lastdev = dev;
	if ((lastname = devname(dev, S_IFCHR)) == NULL)
		lastname = "??";
	return (lastname);
}

void
usage(void)
{
	(void)fprintf(stderr,
	    "usage: lastcomm [-f file] [command ...] [user ...] [terminal ...]\n");
	exit(1);
}