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
36 static 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
43 static 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
72 void done(int);
73 void do_write(int, char *, char *, const char *);
74 static void usage(void);
75 int term_chk(int, char *, int *, time_t *, int);
76 void wr_fputs(wchar_t *s);
77 void search_utmp(int, char *, char *, char *, uid_t);
78 int utmp_chk(char *, char *);
79
80 int
main(int argc,char ** argv)81 main(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
190 static void
usage(void)191 usage(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 */
201 int
utmp_chk(char * user,char * tty)202 utmp_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 */
228 void
search_utmp(int devfd,char * user,char * tty,char * mytty,uid_t myuid)229 search_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 */
276 int
term_chk(int devfd,char * tty,int * msgsokP,time_t * atimeP,int showerror)277 term_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 */
294 void
do_write(int devfd,char * tty,char * mytty,const char * login)295 do_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 */
330 void
done(int n __unused)331 done(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 */
341 void
wr_fputs(wchar_t * s)342 wr_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