1/*-
2 * SPDX-License-Identifier: BSD-3-Clause
3 *
4 * Copyright (c) 1989, 1993
5 *	The Regents of the University of California.  All rights reserved.
6 *
7 * This code is derived from software contributed to Berkeley by
8 * Jef Poskanzer and Craig Leres of the Lawrence Berkeley Laboratory.
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 * 3. Neither the name of the University nor the names of its contributors
19 *    may be used to endorse or promote products derived from this software
20 *    without specific prior written permission.
21 *
22 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
25 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32 * SUCH DAMAGE.
33 */
34
35#ifndef lint
36static const char copyright[] =
37"@(#) Copyright (c) 1989, 1993\n\
38	The Regents of the University of California.  All rights reserved.\n";
39#endif
40
41#if 0
42#ifndef lint
43static char sccsid[] = "@(#)write.c	8.1 (Berkeley) 6/6/93";
44#endif
45#endif
46
47#include <sys/cdefs.h>
48__FBSDID("$FreeBSD$");
49
50#include <sys/param.h>
51#include <sys/capsicum.h>
52#include <sys/filio.h>
53#include <sys/signal.h>
54#include <sys/stat.h>
55#include <sys/time.h>
56
57#include <capsicum_helpers.h>
58#include <ctype.h>
59#include <err.h>
60#include <errno.h>
61#include <locale.h>
62#include <paths.h>
63#include <pwd.h>
64#include <stdio.h>
65#include <stdlib.h>
66#include <string.h>
67#include <unistd.h>
68#include <utmpx.h>
69#include <wchar.h>
70#include <wctype.h>
71
72void done(int);
73void do_write(int, char *, char *, const char *);
74static void usage(void);
75int term_chk(int, char *, int *, time_t *, int);
76void wr_fputs(wchar_t *s);
77void search_utmp(int, char *, char *, char *, uid_t);
78int utmp_chk(char *, char *);
79
80int
81main(int argc, char **argv)
82{
83	unsigned long cmds[] = { TIOCGETA, TIOCGWINSZ, FIODGNAME };
84	cap_rights_t rights;
85	struct passwd *pwd;
86	time_t atime;
87	uid_t myuid;
88	int msgsok, myttyfd;
89	char tty[MAXPATHLEN], *mytty;
90	const char *login;
91	int devfd;
92
93	(void)setlocale(LC_CTYPE, "");
94
95	devfd = open(_PATH_DEV, O_RDONLY);
96	if (devfd < 0)
97		err(1, "open(/dev)");
98	cap_rights_init(&rights, CAP_FCNTL, CAP_FSTAT, CAP_IOCTL, CAP_LOOKUP,
99	    CAP_PWRITE);
100	if (caph_rights_limit(devfd, &rights) < 0)
101		err(1, "can't limit devfd rights");
102
103	/*
104	 * Can't use capsicum helpers here because we need the additional
105	 * FIODGNAME ioctl.
106	 */
107	cap_rights_init(&rights, CAP_FCNTL, CAP_FSTAT, CAP_IOCTL, CAP_READ,
108	    CAP_WRITE);
109	if (caph_rights_limit(STDIN_FILENO, &rights) < 0 ||
110	    caph_rights_limit(STDOUT_FILENO, &rights) < 0 ||
111	    caph_rights_limit(STDERR_FILENO, &rights) < 0 ||
112	    caph_ioctls_limit(STDIN_FILENO, cmds, nitems(cmds)) < 0 ||
113	    caph_ioctls_limit(STDOUT_FILENO, cmds, nitems(cmds)) < 0 ||
114	    caph_ioctls_limit(STDERR_FILENO, cmds, nitems(cmds)) < 0 ||
115	    caph_fcntls_limit(STDIN_FILENO, CAP_FCNTL_GETFL) < 0 ||
116	    caph_fcntls_limit(STDOUT_FILENO, CAP_FCNTL_GETFL) < 0 ||
117	    caph_fcntls_limit(STDERR_FILENO, CAP_FCNTL_GETFL) < 0)
118		err(1, "can't limit stdio rights");
119
120	caph_cache_catpages();
121	caph_cache_tzdata();
122
123	/*
124	 * Cache UTX database fds.
125	 */
126	setutxent();
127
128	/*
129	 * Determine our login name before we reopen() stdout
130	 * and before entering capability sandbox.
131	 */
132	myuid = getuid();
133	if ((login = getlogin()) == NULL) {
134		if ((pwd = getpwuid(myuid)))
135			login = pwd->pw_name;
136		else
137			login = "???";
138	}
139
140	if (caph_enter() < 0)
141		err(1, "cap_enter");
142
143	while (getopt(argc, argv, "") != -1)
144		usage();
145	argc -= optind;
146	argv += optind;
147
148	/* check that sender has write enabled */
149	if (isatty(fileno(stdin)))
150		myttyfd = fileno(stdin);
151	else if (isatty(fileno(stdout)))
152		myttyfd = fileno(stdout);
153	else if (isatty(fileno(stderr)))
154		myttyfd = fileno(stderr);
155	else
156		errx(1, "can't find your tty");
157	if (!(mytty = ttyname(myttyfd)))
158		errx(1, "can't find your tty's name");
159	if (!strncmp(mytty, _PATH_DEV, strlen(_PATH_DEV)))
160		mytty += strlen(_PATH_DEV);
161	if (term_chk(devfd, mytty, &msgsok, &atime, 1))
162		exit(1);
163	if (!msgsok)
164		errx(1, "you have write permission turned off");
165
166	/* check args */
167	switch (argc) {
168	case 1:
169		search_utmp(devfd, argv[0], tty, mytty, myuid);
170		do_write(devfd, tty, mytty, login);
171		break;
172	case 2:
173		if (!strncmp(argv[1], _PATH_DEV, strlen(_PATH_DEV)))
174			argv[1] += strlen(_PATH_DEV);
175		if (utmp_chk(argv[0], argv[1]))
176			errx(1, "%s is not logged in on %s", argv[0], argv[1]);
177		if (term_chk(devfd, argv[1], &msgsok, &atime, 1))
178			exit(1);
179		if (myuid && !msgsok)
180			errx(1, "%s has messages disabled on %s", argv[0], argv[1]);
181		do_write(devfd, argv[1], mytty, login);
182		break;
183	default:
184		usage();
185	}
186	done(0);
187	return (0);
188}
189
190static void
191usage(void)
192{
193	(void)fprintf(stderr, "usage: write user [tty]\n");
194	exit(1);
195}
196
197/*
198 * utmp_chk - checks that the given user is actually logged in on
199 *     the given tty
200 */
201int
202utmp_chk(char *user, char *tty)
203{
204	struct utmpx lu, *u;
205
206	strncpy(lu.ut_line, tty, sizeof lu.ut_line);
207	while ((u = getutxline(&lu)) != NULL)
208		if (u->ut_type == USER_PROCESS &&
209		    strcmp(user, u->ut_user) == 0) {
210			endutxent();
211			return(0);
212		}
213	endutxent();
214	return(1);
215}
216
217/*
218 * search_utmp - search utmp for the "best" terminal to write to
219 *
220 * Ignores terminals with messages disabled, and of the rest, returns
221 * the one with the most recent access time.  Returns as value the number
222 * of the user's terminals with messages enabled, or -1 if the user is
223 * not logged in at all.
224 *
225 * Special case for writing to yourself - ignore the terminal you're
226 * writing from, unless that's the only terminal with messages enabled.
227 */
228void
229search_utmp(int devfd, char *user, char *tty, char *mytty, uid_t myuid)
230{
231	struct utmpx *u;
232	time_t bestatime, atime;
233	int nloggedttys, nttys, msgsok, user_is_me;
234
235	nloggedttys = nttys = 0;
236	bestatime = 0;
237	user_is_me = 0;
238
239	while ((u = getutxent()) != NULL)
240		if (u->ut_type == USER_PROCESS &&
241		    strcmp(user, u->ut_user) == 0) {
242			++nloggedttys;
243			if (term_chk(devfd, u->ut_line, &msgsok, &atime, 0))
244				continue;	/* bad term? skip */
245			if (myuid && !msgsok)
246				continue;	/* skip ttys with msgs off */
247			if (strcmp(u->ut_line, mytty) == 0) {
248				user_is_me = 1;
249				continue;	/* don't write to yourself */
250			}
251			++nttys;
252			if (atime > bestatime) {
253				bestatime = atime;
254				(void)strlcpy(tty, u->ut_line, MAXPATHLEN);
255			}
256		}
257	endutxent();
258
259	if (nloggedttys == 0)
260		errx(1, "%s is not logged in", user);
261	if (nttys == 0) {
262		if (user_is_me) {		/* ok, so write to yourself! */
263			(void)strlcpy(tty, mytty, MAXPATHLEN);
264			return;
265		}
266		errx(1, "%s has messages disabled", user);
267	} else if (nttys > 1) {
268		warnx("%s is logged in more than once; writing to %s", user, tty);
269	}
270}
271
272/*
273 * term_chk - check that a terminal exists, and get the message bit
274 *     and the access time
275 */
276int
277term_chk(int devfd, char *tty, int *msgsokP, time_t *atimeP, int showerror)
278{
279	struct stat s;
280
281	if (fstatat(devfd, tty, &s, 0) < 0) {
282		if (showerror)
283			warn("%s%s", _PATH_DEV, tty);
284		return(1);
285	}
286	*msgsokP = (s.st_mode & (S_IWRITE >> 3)) != 0;	/* group write bit */
287	*atimeP = s.st_atime;
288	return(0);
289}
290
291/*
292 * do_write - actually make the connection
293 */
294void
295do_write(int devfd, char *tty, char *mytty, const char *login)
296{
297	char *nows;
298	time_t now;
299	char host[MAXHOSTNAMELEN];
300	wchar_t line[512];
301	int fd;
302
303	fd = openat(devfd, tty, O_WRONLY);
304	if (fd < 0)
305		err(1, "openat(%s%s)", _PATH_DEV, tty);
306	fclose(stdout);
307	stdout = fdopen(fd, "w");
308	if (stdout == NULL)
309		err(1, "%s%s", _PATH_DEV, tty);
310
311	(void)signal(SIGINT, done);
312	(void)signal(SIGHUP, done);
313
314	/* print greeting */
315	if (gethostname(host, sizeof(host)) < 0)
316		(void)strcpy(host, "???");
317	now = time((time_t *)NULL);
318	nows = ctime(&now);
319	nows[16] = '\0';
320	(void)printf("\r\n\007\007\007Message from %s@%s on %s at %s ...\r\n",
321	    login, host, mytty, nows + 11);
322
323	while (fgetws(line, sizeof(line)/sizeof(wchar_t), stdin) != NULL)
324		wr_fputs(line);
325}
326
327/*
328 * done - cleanup and exit
329 */
330void
331done(int n __unused)
332{
333	(void)printf("EOF\r\n");
334	exit(0);
335}
336
337/*
338 * wr_fputs - like fputs(), but makes control characters visible and
339 *     turns \n into \r\n
340 */
341void
342wr_fputs(wchar_t *s)
343{
344
345#define	PUTC(c)	if (putwchar(c) == WEOF) err(1, NULL);
346
347	for (; *s != L'\0'; ++s) {
348		if (*s == L'\n') {
349			PUTC(L'\r');
350			PUTC(L'\n');
351		} else if (iswprint(*s) || iswspace(*s)) {
352			PUTC(*s);
353		} else {
354			wprintf(L"<0x%X>", *s);
355		}
356	}
357	return;
358#undef PUTC
359}
360