write.c revision 173572 
1/*
2 * Copyright (c) 1989, 1993
3 *	The Regents of the University of California.  All rights reserved.
4 *
5 * This code is derived from software contributed to Berkeley by
6 * Jef Poskanzer and Craig Leres of the Lawrence Berkeley Laboratory.
7 *
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
10 * are met:
11 * 1. Redistributions of source code must retain the above copyright
12 *    notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 *    notice, this list of conditions and the following disclaimer in the
15 *    documentation and/or other materials provided with the distribution.
16 * 3. All advertising materials mentioning features or use of this software
17 *    must display the following acknowledgement:
18 *	This product includes software developed by the University of
19 *	California, Berkeley and its contributors.
20 * 4. Neither the name of the University nor the names of its contributors
21 *    may be used to endorse or promote products derived from this software
22 *    without specific prior written permission.
23 *
24 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
25 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
26 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
27 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
28 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
29 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
30 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
31 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
32 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
33 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
34 * SUCH DAMAGE.
35 */
36
37#ifndef lint
38static const char copyright[] =
39"@(#) Copyright (c) 1989, 1993\n\
40	The Regents of the University of California.  All rights reserved.\n";
41#endif
42
43#if 0
44#ifndef lint
45static char sccsid[] = "@(#)write.c	8.1 (Berkeley) 6/6/93";
46#endif
47#endif
48
49#include <sys/cdefs.h>
50__FBSDID("$FreeBSD: head/usr.bin/write/write.c 173572 2007-11-12 20:02:21Z jhb $");
51
52#include <sys/param.h>
53#include <sys/signal.h>
54#include <sys/stat.h>
55#include <sys/file.h>
56#include <sys/time.h>
57#include <ctype.h>
58#include <err.h>
59#include <locale.h>
60#include <paths.h>
61#include <pwd.h>
62#include <stdio.h>
63#include <stdlib.h>
64#include <string.h>
65#include <unistd.h>
66#include <utmp.h>
67
68void done(int);
69void do_write(char *, char *, uid_t);
70static void usage(void);
71int term_chk(char *, int *, time_t *, int);
72void wr_fputs(unsigned char *s);
73void search_utmp(char *, char *, char *, uid_t);
74int utmp_chk(char *, char *);
75
76int
77main(int argc, char **argv)
78{
79	time_t atime;
80	uid_t myuid;
81	int msgsok, myttyfd;
82	char tty[MAXPATHLEN], *mytty;
83
84	(void)setlocale(LC_CTYPE, "");
85
86	while (getopt(argc, argv, "") != -1)
87		usage();
88	argc -= optind;
89	argv += optind;
90
91	/* check that sender has write enabled */
92	if (isatty(fileno(stdin)))
93		myttyfd = fileno(stdin);
94	else if (isatty(fileno(stdout)))
95		myttyfd = fileno(stdout);
96	else if (isatty(fileno(stderr)))
97		myttyfd = fileno(stderr);
98	else
99		errx(1, "can't find your tty");
100	if (!(mytty = ttyname(myttyfd)))
101		errx(1, "can't find your tty's name");
102	if (!strncmp(mytty, _PATH_DEV, strlen(_PATH_DEV)))
103		mytty += strlen(_PATH_DEV);
104	if (term_chk(mytty, &msgsok, &atime, 1))
105		exit(1);
106	if (!msgsok)
107		errx(1, "you have write permission turned off");
108
109	myuid = getuid();
110
111	/* check args */
112	switch (argc) {
113	case 1:
114		search_utmp(argv[0], tty, mytty, myuid);
115		do_write(tty, mytty, myuid);
116		break;
117	case 2:
118		if (!strncmp(argv[1], _PATH_DEV, strlen(_PATH_DEV)))
119			argv[1] += strlen(_PATH_DEV);
120		if (utmp_chk(argv[0], argv[1]))
121			errx(1, "%s is not logged in on %s", argv[0], argv[1]);
122		if (term_chk(argv[1], &msgsok, &atime, 1))
123			exit(1);
124		if (myuid && !msgsok)
125			errx(1, "%s has messages disabled on %s", argv[0], argv[1]);
126		do_write(argv[1], mytty, myuid);
127		break;
128	default:
129		usage();
130	}
131	done(0);
132	return (0);
133}
134
135static void
136usage(void)
137{
138	(void)fprintf(stderr, "usage: write user [tty]\n");
139	exit(1);
140}
141
142/*
143 * utmp_chk - checks that the given user is actually logged in on
144 *     the given tty
145 */
146int
147utmp_chk(char *user, char *tty)
148{
149	struct utmp u;
150	int ufd;
151
152	if ((ufd = open(_PATH_UTMP, O_RDONLY)) < 0)
153		return(0);	/* ignore error, shouldn't happen anyway */
154
155	while (read(ufd, (char *) &u, sizeof(u)) == sizeof(u))
156		if (strncmp(user, u.ut_name, sizeof(u.ut_name)) == 0 &&
157		    strncmp(tty, u.ut_line, sizeof(u.ut_line)) == 0) {
158			(void)close(ufd);
159			return(0);
160		}
161
162	(void)close(ufd);
163	return(1);
164}
165
166/*
167 * search_utmp - search utmp for the "best" terminal to write to
168 *
169 * Ignores terminals with messages disabled, and of the rest, returns
170 * the one with the most recent access time.  Returns as value the number
171 * of the user's terminals with messages enabled, or -1 if the user is
172 * not logged in at all.
173 *
174 * Special case for writing to yourself - ignore the terminal you're
175 * writing from, unless that's the only terminal with messages enabled.
176 */
177void
178search_utmp(char *user, char *tty, char *mytty, uid_t myuid)
179{
180	struct utmp u;
181	time_t bestatime, atime;
182	int ufd, nloggedttys, nttys, msgsok, user_is_me;
183	char atty[UT_LINESIZE + 1];
184
185	if ((ufd = open(_PATH_UTMP, O_RDONLY)) < 0)
186		err(1, "utmp");
187
188	nloggedttys = nttys = 0;
189	bestatime = 0;
190	user_is_me = 0;
191	while (read(ufd, (char *) &u, sizeof(u)) == sizeof(u))
192		if (strncmp(user, u.ut_name, sizeof(u.ut_name)) == 0) {
193			++nloggedttys;
194			(void)strncpy(atty, u.ut_line, UT_LINESIZE);
195			atty[UT_LINESIZE] = '\0';
196			if (term_chk(atty, &msgsok, &atime, 0))
197				continue;	/* bad term? skip */
198			if (myuid && !msgsok)
199				continue;	/* skip ttys with msgs off */
200			if (strcmp(atty, mytty) == 0) {
201				user_is_me = 1;
202				continue;	/* don't write to yourself */
203			}
204			++nttys;
205			if (atime > bestatime) {
206				bestatime = atime;
207				(void)strcpy(tty, atty);
208			}
209		}
210
211	(void)close(ufd);
212	if (nloggedttys == 0)
213		errx(1, "%s is not logged in", user);
214	if (nttys == 0) {
215		if (user_is_me) {		/* ok, so write to yourself! */
216			(void)strcpy(tty, mytty);
217			return;
218		}
219		errx(1, "%s has messages disabled", user);
220	} else if (nttys > 1) {
221		warnx("%s is logged in more than once; writing to %s", user, tty);
222	}
223}
224
225/*
226 * term_chk - check that a terminal exists, and get the message bit
227 *     and the access time
228 */
229int
230term_chk(char *tty, int *msgsokP, time_t *atimeP, int showerror)
231{
232	struct stat s;
233	char path[MAXPATHLEN];
234
235	(void)snprintf(path, sizeof(path), "%s%s", _PATH_DEV, tty);
236	if (stat(path, &s) < 0) {
237		if (showerror)
238			warn("%s", path);
239		return(1);
240	}
241	*msgsokP = (s.st_mode & (S_IWRITE >> 3)) != 0;	/* group write bit */
242	*atimeP = s.st_atime;
243	return(0);
244}
245
246/*
247 * do_write - actually make the connection
248 */
249void
250do_write(char *tty, char *mytty, uid_t myuid)
251{
252	const char *login;
253	char *nows;
254	struct passwd *pwd;
255	time_t now;
256	char path[MAXPATHLEN], host[MAXHOSTNAMELEN], line[512];
257
258	/* Determine our login name before we reopen() stdout */
259	if ((login = getlogin()) == NULL) {
260		if ((pwd = getpwuid(myuid)))
261			login = pwd->pw_name;
262		else
263			login = "???";
264	}
265
266	(void)snprintf(path, sizeof(path), "%s%s", _PATH_DEV, tty);
267	if ((freopen(path, "w", stdout)) == NULL)
268		err(1, "%s", path);
269
270	(void)signal(SIGINT, done);
271	(void)signal(SIGHUP, done);
272
273	/* print greeting */
274	if (gethostname(host, sizeof(host)) < 0)
275		(void)strcpy(host, "???");
276	now = time((time_t *)NULL);
277	nows = ctime(&now);
278	nows[16] = '\0';
279	(void)printf("\r\n\007\007\007Message from %s@%s on %s at %s ...\r\n",
280	    login, host, mytty, nows + 11);
281
282	while (fgets(line, sizeof(line), stdin) != NULL)
283		wr_fputs(line);
284}
285
286/*
287 * done - cleanup and exit
288 */
289void
290done(int n __unused)
291{
292	(void)printf("EOF\r\n");
293	exit(0);
294}
295
296/*
297 * wr_fputs - like fputs(), but makes control characters visible and
298 *     turns \n into \r\n
299 */
300void
301wr_fputs(unsigned char *s)
302{
303
304#define	PUTC(c)	if (putchar(c) == EOF) err(1, NULL);
305
306	for (; *s != '\0'; ++s) {
307		if (*s == '\n') {
308			PUTC('\r');
309		} else if (((*s & 0x80) && *s < 0xA0) ||
310			   /* disable upper controls */
311			   (!isprint(*s) && !isspace(*s) &&
312			    *s != '\a' && *s != '\b')
313			  ) {
314			if (*s & 0x80) {
315				*s &= ~0x80;
316				PUTC('M');
317				PUTC('-');
318			}
319			if (iscntrl(*s)) {
320				*s ^= 0x40;
321				PUTC('^');
322			}
323		}
324		PUTC(*s);
325	}
326	return;
327#undef PUTC
328}
329