xref: /freebsd/usr.bin/write/write.c (revision e4e9813eb92cd7c4d4b819a8fbed5cbd3d92f5d8)
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
38 static 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
45 static char sccsid[] = "@(#)write.c	8.1 (Berkeley) 6/6/93";
46 #endif
47 #endif
48 
49 #include <sys/cdefs.h>
50 __FBSDID("$FreeBSD$");
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 
68 void done(int);
69 void do_write(char *, char *, uid_t);
70 static void usage(void);
71 int term_chk(char *, int *, time_t *, int);
72 void wr_fputs(unsigned char *s);
73 void search_utmp(char *, char *, char *, uid_t);
74 int utmp_chk(char *, char *);
75 
76 int
77 main(int argc, char **argv)
78 {
79 	char *cp;
80 	time_t atime;
81 	uid_t myuid;
82 	int msgsok, myttyfd;
83 	char tty[MAXPATHLEN], *mytty;
84 
85 	(void)setlocale(LC_CTYPE, "");
86 
87 	while (getopt(argc, argv, "") != -1)
88 		usage();
89 	argc -= optind;
90 	argv += optind;
91 
92 	/* check that sender has write enabled */
93 	if (isatty(fileno(stdin)))
94 		myttyfd = fileno(stdin);
95 	else if (isatty(fileno(stdout)))
96 		myttyfd = fileno(stdout);
97 	else if (isatty(fileno(stderr)))
98 		myttyfd = fileno(stderr);
99 	else
100 		errx(1, "can't find your tty");
101 	if (!(mytty = ttyname(myttyfd)))
102 		errx(1, "can't find your tty's name");
103 	if ((cp = rindex(mytty, '/')))
104 		mytty = cp + 1;
105 	if (term_chk(mytty, &msgsok, &atime, 1))
106 		exit(1);
107 	if (!msgsok)
108 		errx(1, "you have write permission turned off");
109 
110 	myuid = getuid();
111 
112 	/* check args */
113 	switch (argc) {
114 	case 1:
115 		search_utmp(argv[0], tty, mytty, myuid);
116 		do_write(tty, mytty, myuid);
117 		break;
118 	case 2:
119 		if (!strncmp(argv[1], _PATH_DEV, strlen(_PATH_DEV)))
120 			argv[1] += strlen(_PATH_DEV);
121 		if (utmp_chk(argv[0], argv[1]))
122 			errx(1, "%s is not logged in on %s", argv[0], argv[1]);
123 		if (term_chk(argv[1], &msgsok, &atime, 1))
124 			exit(1);
125 		if (myuid && !msgsok)
126 			errx(1, "%s has messages disabled on %s", argv[0], argv[1]);
127 		do_write(argv[1], mytty, myuid);
128 		break;
129 	default:
130 		usage();
131 	}
132 	done(0);
133 	return (0);
134 }
135 
136 static void
137 usage(void)
138 {
139 	(void)fprintf(stderr, "usage: write user [tty]\n");
140 	exit(1);
141 }
142 
143 /*
144  * utmp_chk - checks that the given user is actually logged in on
145  *     the given tty
146  */
147 int
148 utmp_chk(char *user, char *tty)
149 {
150 	struct utmp u;
151 	int ufd;
152 
153 	if ((ufd = open(_PATH_UTMP, O_RDONLY)) < 0)
154 		return(0);	/* ignore error, shouldn't happen anyway */
155 
156 	while (read(ufd, (char *) &u, sizeof(u)) == sizeof(u))
157 		if (strncmp(user, u.ut_name, sizeof(u.ut_name)) == 0 &&
158 		    strncmp(tty, u.ut_line, sizeof(u.ut_line)) == 0) {
159 			(void)close(ufd);
160 			return(0);
161 		}
162 
163 	(void)close(ufd);
164 	return(1);
165 }
166 
167 /*
168  * search_utmp - search utmp for the "best" terminal to write to
169  *
170  * Ignores terminals with messages disabled, and of the rest, returns
171  * the one with the most recent access time.  Returns as value the number
172  * of the user's terminals with messages enabled, or -1 if the user is
173  * not logged in at all.
174  *
175  * Special case for writing to yourself - ignore the terminal you're
176  * writing from, unless that's the only terminal with messages enabled.
177  */
178 void
179 search_utmp(char *user, char *tty, char *mytty, uid_t myuid)
180 {
181 	struct utmp u;
182 	time_t bestatime, atime;
183 	int ufd, nloggedttys, nttys, msgsok, user_is_me;
184 	char atty[UT_LINESIZE + 1];
185 
186 	if ((ufd = open(_PATH_UTMP, O_RDONLY)) < 0)
187 		err(1, "utmp");
188 
189 	nloggedttys = nttys = 0;
190 	bestatime = 0;
191 	user_is_me = 0;
192 	while (read(ufd, (char *) &u, sizeof(u)) == sizeof(u))
193 		if (strncmp(user, u.ut_name, sizeof(u.ut_name)) == 0) {
194 			++nloggedttys;
195 			(void)strncpy(atty, u.ut_line, UT_LINESIZE);
196 			atty[UT_LINESIZE] = '\0';
197 			if (term_chk(atty, &msgsok, &atime, 0))
198 				continue;	/* bad term? skip */
199 			if (myuid && !msgsok)
200 				continue;	/* skip ttys with msgs off */
201 			if (strcmp(atty, mytty) == 0) {
202 				user_is_me = 1;
203 				continue;	/* don't write to yourself */
204 			}
205 			++nttys;
206 			if (atime > bestatime) {
207 				bestatime = atime;
208 				(void)strcpy(tty, atty);
209 			}
210 		}
211 
212 	(void)close(ufd);
213 	if (nloggedttys == 0)
214 		errx(1, "%s is not logged in", user);
215 	if (nttys == 0) {
216 		if (user_is_me) {		/* ok, so write to yourself! */
217 			(void)strcpy(tty, mytty);
218 			return;
219 		}
220 		errx(1, "%s has messages disabled", user);
221 	} else if (nttys > 1) {
222 		warnx("%s is logged in more than once; writing to %s", user, tty);
223 	}
224 }
225 
226 /*
227  * term_chk - check that a terminal exists, and get the message bit
228  *     and the access time
229  */
230 int
231 term_chk(char *tty, int *msgsokP, time_t *atimeP, int showerror)
232 {
233 	struct stat s;
234 	char path[MAXPATHLEN];
235 
236 	(void)snprintf(path, sizeof(path), "%s%s", _PATH_DEV, tty);
237 	if (stat(path, &s) < 0) {
238 		if (showerror)
239 			warn("%s", path);
240 		return(1);
241 	}
242 	*msgsokP = (s.st_mode & (S_IWRITE >> 3)) != 0;	/* group write bit */
243 	*atimeP = s.st_atime;
244 	return(0);
245 }
246 
247 /*
248  * do_write - actually make the connection
249  */
250 void
251 do_write(char *tty, char *mytty, uid_t myuid)
252 {
253 	const char *login;
254 	char *nows;
255 	struct passwd *pwd;
256 	time_t now;
257 	char path[MAXPATHLEN], host[MAXHOSTNAMELEN], line[512];
258 
259 	/* Determine our login name before we reopen() stdout */
260 	if ((login = getlogin()) == NULL) {
261 		if ((pwd = getpwuid(myuid)))
262 			login = pwd->pw_name;
263 		else
264 			login = "???";
265 	}
266 
267 	(void)snprintf(path, sizeof(path), "%s%s", _PATH_DEV, tty);
268 	if ((freopen(path, "w", stdout)) == NULL)
269 		err(1, "%s", path);
270 
271 	(void)signal(SIGINT, done);
272 	(void)signal(SIGHUP, done);
273 
274 	/* print greeting */
275 	if (gethostname(host, sizeof(host)) < 0)
276 		(void)strcpy(host, "???");
277 	now = time((time_t *)NULL);
278 	nows = ctime(&now);
279 	nows[16] = '\0';
280 	(void)printf("\r\n\007\007\007Message from %s@%s on %s at %s ...\r\n",
281 	    login, host, mytty, nows + 11);
282 
283 	while (fgets(line, sizeof(line), stdin) != NULL)
284 		wr_fputs(line);
285 }
286 
287 /*
288  * done - cleanup and exit
289  */
290 void
291 done(int n __unused)
292 {
293 	(void)printf("EOF\r\n");
294 	exit(0);
295 }
296 
297 /*
298  * wr_fputs - like fputs(), but makes control characters visible and
299  *     turns \n into \r\n
300  */
301 void
302 wr_fputs(unsigned char *s)
303 {
304 
305 #define	PUTC(c)	if (putchar(c) == EOF) err(1, NULL);
306 
307 	for (; *s != '\0'; ++s) {
308 		if (*s == '\n') {
309 			PUTC('\r');
310 		} else if (((*s & 0x80) && *s < 0xA0) ||
311 			   /* disable upper controls */
312 			   (!isprint(*s) && !isspace(*s) &&
313 			    *s != '\a' && *s != '\b')
314 			  ) {
315 			if (*s & 0x80) {
316 				*s &= ~0x80;
317 				PUTC('M');
318 				PUTC('-');
319 			}
320 			if (iscntrl(*s)) {
321 				*s ^= 0x40;
322 				PUTC('^');
323 			}
324 		}
325 		PUTC(*s);
326 	}
327 	return;
328 #undef PUTC
329 }
330