1/*	$NetBSD: utmp_update.c,v 1.14 2023/09/29 12:08:03 christos Exp $	 */
2
3/*-
4 * Copyright (c) 2002 The NetBSD Foundation, Inc.
5 * All rights reserved.
6 *
7 * This code is derived from software contributed to The NetBSD Foundation
8 * by Christos Zoulas.
9 *
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
12 * are met:
13 * 1. Redistributions of source code must retain the above copyright
14 *    notice, this list of conditions and the following disclaimer.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 *    notice, this list of conditions and the following disclaimer in the
17 *    documentation and/or other materials provided with the distribution.
18 *
19 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
20 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
21 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
22 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
23 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
24 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
25 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
26 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
27 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
28 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
29 * POSSIBILITY OF SUCH DAMAGE.
30 */
31#include <sys/cdefs.h>
32
33__RCSID("$NetBSD: utmp_update.c,v 1.14 2023/09/29 12:08:03 christos Exp $");
34
35#include <sys/types.h>
36#include <sys/param.h>
37#include <sys/stat.h>
38
39#include <stdio.h>
40#include <vis.h>
41#include <err.h>
42#include <fcntl.h>
43#include <pwd.h>
44#include <ctype.h>
45#include <utmpx.h>
46#include <stdlib.h>
47#include <string.h>
48#include <unistd.h>
49#include <paths.h>
50#include <stdarg.h>
51#include <errno.h>
52#include <syslog.h>
53
54static __dead __printflike(2, 3) void
55logerr(int e, const char *fmt, ...)
56{
57	va_list sap, eap;
58	char *s = NULL;
59
60	if (e)
61		(void)asprintf(&s, "%s (%s)", fmt, strerror(e));
62	if (s)
63		fmt = s;
64
65	va_start(sap, fmt);
66	va_copy(eap, sap);
67	vsyslog(LOG_ERR, fmt, sap);
68	va_end(sap);
69	verrx(1, fmt, eap);
70	va_end(eap);
71}
72
73int
74main(int argc, char *argv[])
75{
76	struct utmpx *utx;
77	size_t len;
78	struct passwd *pwd;
79	struct stat st;
80	int fd;
81	int res;
82	uid_t euid, ruid;
83	char tty[MAXPATHLEN];
84	const char *p, *ep;
85
86	euid = geteuid();
87	ruid = getuid();
88
89	if (argc != 2) {
90		(void)fprintf(stderr, "Usage: %s <vis-utmpx-entry>\n",
91		    getprogname());
92		return 1;
93	}
94
95	openlog(getprogname(), LOG_PID | LOG_NDELAY, LOG_AUTH);
96	if (seteuid(ruid) == -1)
97		logerr(errno, "Can't setuid %ld", (long)ruid);
98
99	len = strlen(argv[1]);
100
101	if (len > sizeof(*utx) * 4 + 1 || len < sizeof(*utx))
102		logerr(0, "Bad argument size %zu", len);
103
104	if ((utx = malloc(len+1)) == NULL)
105		logerr(errno, "Can't allocate %zu", len+1);
106
107	res = strunvis((char *)utx, argv[1]);
108	if (res != (int)sizeof(*utx))
109		logerr(0, "Decoding error %s %d != %zu", argv[1], res,
110		    sizeof(*utx));
111
112	switch (utx->ut_type) {
113	case USER_PROCESS:
114	case DEAD_PROCESS:
115		break;
116	default:
117		logerr(0, "Invalid utmpx type %d", (int)utx->ut_type);
118	}
119
120	p = utx->ut_host;
121	ep = p + sizeof(utx->ut_host);
122	for (; p < ep && *p; p++)
123		if (!isprint((unsigned char)*p))
124			logerr(0, "Non-printable characters in hostname");
125
126	if (ruid != 0) {
127		if ((pwd = getpwuid(ruid)) == NULL)
128			logerr(0, "User %ld does not exist in password"
129			    " database", (long)ruid);
130
131		if (strcmp(pwd->pw_name, utx->ut_name) != 0)
132			logerr(0, "Current user `%s' does not match "
133			    "`%s' in utmpx entry", pwd->pw_name, utx->ut_name);
134	}
135
136	(void)snprintf(tty, sizeof(tty), "%s%s", _PATH_DEV, utx->ut_line);
137	fd = open(tty, O_RDONLY|O_NONBLOCK, 0);
138	if (fd != -1) {
139		if (fstat(fd, &st) == -1)
140			logerr(errno, "Cannot stat `%s'", tty);
141		if (ruid != 0 && st.st_uid != ruid)
142			logerr(0, "%s: Is not owned by you", tty);
143		if (!isatty(fd))
144			logerr(0, "%s: Not a tty device", tty);
145		(void)close(fd);
146		if (access(tty, W_OK|R_OK) == -1)
147			logerr(errno, "Can't access `%s'", tty);
148	} else {
149		struct utmpx utold, *utoldp;
150		pid_t ppid;
151
152		/*
153		 * A daemon like ftpd that does not use a tty line?
154		 * We only allow it to kill its own existing entries
155		 */
156		if (utx->ut_type != DEAD_PROCESS)
157			logerr(errno, "Cannot open `%s'", tty);
158
159		(void)memcpy(utold.ut_line, utx->ut_line, sizeof(utx->ut_line));
160		if ((utoldp = getutxline(&utold)) == NULL)
161			logerr(0, "Cannot find existing entry for `%s'",
162			    utx->ut_line);
163		if (utoldp->ut_pid != (ppid = getppid()))
164			logerr(0, "Cannot modify entry for `%s' "
165			    "utmp pid %ld != parent %ld", tty,
166			    (long)utoldp->ut_pid, (long)ppid);
167	}
168
169	if (seteuid(euid) == 1)
170		logerr(errno, "Can't setuid %ld", (long)euid);
171	if (pututxline(utx) == NULL)
172		logerr(errno, "Cannot update utmp entry");
173
174	return 0;
175}
176