/*      $NetBSD: utmp_update.c,v 1.15 2026/05/07 15:00:13 shm Exp $      */

/*-
 * Copyright (c) 2002 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Christos Zoulas.
 *
 * 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. 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 FOUNDATION 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/cdefs.h>

__RCSID("$NetBSD: utmp_update.c,v 1.15 2026/05/07 15:00:13 shm Exp $");

#include <sys/types.h>
#include <sys/param.h>
#include <sys/stat.h>

#include <stdio.h>
#include <vis.h>
#include <err.h>
#include <fcntl.h>
#include <pwd.h>
#include <ctype.h>
#include <utmpx.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <paths.h>
#include <stdarg.h>
#include <errno.h>
#include <syslog.h>

static __dead __printflike(2, 3) void
logerr(int e, const char *fmt, ...)
{
        va_list sap, eap;
        char *s = NULL;
        
        if (e)
                (void)asprintf(&s, "%s (%s)", fmt, strerror(e));
        if (s)
                fmt = s;

        va_start(sap, fmt);
        va_copy(eap, sap);
        vsyslog(LOG_ERR, fmt, sap);
        va_end(sap);
        verrx(1, fmt, eap);
        va_end(eap);
}

int
main(int argc, char *argv[])
{
        struct utmpx *utx;
        size_t len;
        struct passwd *pwd;
        struct stat st;
        int fd;
        int res;
        uid_t euid, ruid;
        char tty[MAXPATHLEN];
        const char *p, *ep;

        euid = geteuid();
        ruid = getuid();

        if (argc != 2) {
                (void)fprintf(stderr, "Usage: %s <vis-utmpx-entry>\n",
                    getprogname());
                return 1;
        }

        openlog(getprogname(), LOG_PID | LOG_NDELAY, LOG_AUTH);
        if (seteuid(ruid) == -1)
                logerr(errno, "Can't setuid %ld", (long)ruid);

        len = strlen(argv[1]);

        if (len > sizeof(*utx) * 4 + 1 || len < sizeof(*utx))
                logerr(0, "Bad argument size %zu", len);

        if ((utx = malloc(len+1)) == NULL)
                logerr(errno, "Can't allocate %zu", len+1);

        res = strunvis((char *)utx, argv[1]);
        if (res != (int)sizeof(*utx))
                logerr(0, "Decoding error %s %d != %zu", argv[1], res,
                    sizeof(*utx));

        switch (utx->ut_type) {
        case USER_PROCESS:
        case DEAD_PROCESS:
                break;
        default:
                logerr(0, "Invalid utmpx type %d", (int)utx->ut_type);
        }

        p = utx->ut_host;
        ep = p + sizeof(utx->ut_host);
        for (; p < ep && *p; p++)
                if (!isprint((unsigned char)*p))
                        logerr(0, "Non-printable characters in hostname");

        if (ruid != 0) {
                if ((pwd = getpwuid(ruid)) == NULL)
                        logerr(0, "User %ld does not exist in password"
                            " database", (long)ruid);

                if (strcmp(pwd->pw_name, utx->ut_name) != 0)
                        logerr(0, "Current user `%s' does not match "
                            "`%s' in utmpx entry", pwd->pw_name, utx->ut_name);
        }

        (void)snprintf(tty, sizeof(tty), "%s%s", _PATH_DEV, utx->ut_line);
        fd = open(tty, O_RDONLY|O_NONBLOCK, 0);
        if (fd != -1) {
                if (fstat(fd, &st) == -1)
                        logerr(errno, "Cannot stat `%s'", tty);
                if (ruid != 0 && st.st_uid != ruid)
                        logerr(0, "%s: Is not owned by you", tty);
                if (!isatty(fd))
                        logerr(0, "%s: Not a tty device", tty);
                (void)close(fd);
                if (access(tty, W_OK|R_OK) == -1)
                        logerr(errno, "Can't access `%s'", tty);
        } else {
                struct utmpx utold, *utoldp;
                pid_t ppid;

                /*
                 * A daemon like ftpd that does not use a tty line? 
                 * We only allow it to kill its own existing entries 
                 */
                if (utx->ut_type != DEAD_PROCESS)
                        logerr(errno, "Cannot open `%s'", tty);

                (void)memcpy(utold.ut_line, utx->ut_line, sizeof(utx->ut_line));
                if ((utoldp = getutxline(&utold)) == NULL)
                        logerr(0, "Cannot find existing entry for `%s'",
                            utx->ut_line);
                if (utoldp->ut_pid != (ppid = getppid()))
                        logerr(0, "Cannot modify entry for `%s' "
                            "utmp pid %ld != parent %ld", tty,
                            (long)utoldp->ut_pid, (long)ppid);
        }

        if (seteuid(euid) == -1)
                logerr(errno, "Can't setuid %ld", (long)euid);
        if (pututxline(utx) == NULL)
                logerr(errno, "Cannot update utmp entry");

        return 0;
}