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 #include <sys/param.h>
36 #include <sys/capsicum.h>
37 #include <sys/filio.h>
38 #include <sys/signal.h>
39 #include <sys/stat.h>
40 #include <sys/time.h>
41
42 #include <capsicum_helpers.h>
43 #include <ctype.h>
44 #include <err.h>
45 #include <errno.h>
46 #include <locale.h>
47 #include <paths.h>
48 #include <pwd.h>
49 #include <stdio.h>
50 #include <stdlib.h>
51 #include <string.h>
52 #include <unistd.h>
53 #include <utmpx.h>
54 #include <wchar.h>
55 #include <wctype.h>
56
57 void done(int);
58 void do_write(int, char *, char *, const char *);
59 static void usage(void) __dead2;
60 int term_chk(int, char *, int *, time_t *, int);
61 void wr_fputs(wchar_t *s);
62 void search_utmp(int, char *, char *, char *, uid_t);
63 int utmp_chk(char *, char *);
64
65 int
main(int argc,char ** argv)66 main(int argc, char **argv)
67 {
68 unsigned long cmds[] = { TIOCGETA, TIOCGWINSZ, FIODGNAME };
69 cap_rights_t rights;
70 struct passwd *pwd;
71 time_t atime;
72 uid_t myuid;
73 int msgsok, myttyfd;
74 char tty[MAXPATHLEN], *mytty;
75 const char *login;
76 int devfd;
77
78 (void)setlocale(LC_CTYPE, "");
79
80 devfd = open(_PATH_DEV, O_RDONLY);
81 if (devfd < 0)
82 err(1, "open(/dev)");
83 cap_rights_init(&rights, CAP_FCNTL, CAP_FSTAT, CAP_IOCTL, CAP_LOOKUP,
84 CAP_PWRITE);
85 if (caph_rights_limit(devfd, &rights) < 0)
86 err(1, "can't limit devfd rights");
87
88 /*
89 * Can't use capsicum helpers here because we need the additional
90 * FIODGNAME ioctl.
91 */
92 cap_rights_init(&rights, CAP_FCNTL, CAP_FSTAT, CAP_IOCTL, CAP_READ,
93 CAP_WRITE);
94 if (caph_rights_limit(STDIN_FILENO, &rights) < 0 ||
95 caph_rights_limit(STDOUT_FILENO, &rights) < 0 ||
96 caph_rights_limit(STDERR_FILENO, &rights) < 0 ||
97 caph_ioctls_limit(STDIN_FILENO, cmds, nitems(cmds)) < 0 ||
98 caph_ioctls_limit(STDOUT_FILENO, cmds, nitems(cmds)) < 0 ||
99 caph_ioctls_limit(STDERR_FILENO, cmds, nitems(cmds)) < 0 ||
100 caph_fcntls_limit(STDIN_FILENO, CAP_FCNTL_GETFL) < 0 ||
101 caph_fcntls_limit(STDOUT_FILENO, CAP_FCNTL_GETFL) < 0 ||
102 caph_fcntls_limit(STDERR_FILENO, CAP_FCNTL_GETFL) < 0)
103 err(1, "can't limit stdio rights");
104
105 caph_cache_catpages();
106 caph_cache_tzdata();
107
108 /*
109 * Cache UTX database fds.
110 */
111 setutxent();
112
113 /*
114 * Determine our login name before we reopen() stdout
115 * and before entering capability sandbox.
116 */
117 myuid = getuid();
118 if ((login = getlogin()) == NULL) {
119 if ((pwd = getpwuid(myuid)))
120 login = pwd->pw_name;
121 else
122 login = "???";
123 }
124
125 if (caph_enter() < 0)
126 err(1, "cap_enter");
127
128 while (getopt(argc, argv, "") != -1)
129 usage();
130 argc -= optind;
131 argv += optind;
132
133 /* check that sender has write enabled */
134 if (isatty(fileno(stdin)))
135 myttyfd = fileno(stdin);
136 else if (isatty(fileno(stdout)))
137 myttyfd = fileno(stdout);
138 else if (isatty(fileno(stderr)))
139 myttyfd = fileno(stderr);
140 else
141 errx(1, "can't find your tty");
142 if (!(mytty = ttyname(myttyfd)))
143 errx(1, "can't find your tty's name");
144 if (!strncmp(mytty, _PATH_DEV, strlen(_PATH_DEV)))
145 mytty += strlen(_PATH_DEV);
146 if (term_chk(devfd, mytty, &msgsok, &atime, 1))
147 exit(1);
148 if (!msgsok)
149 errx(1, "you have write permission turned off");
150
151 /* check args */
152 switch (argc) {
153 case 1:
154 search_utmp(devfd, argv[0], tty, mytty, myuid);
155 do_write(devfd, tty, mytty, login);
156 break;
157 case 2:
158 if (!strncmp(argv[1], _PATH_DEV, strlen(_PATH_DEV)))
159 argv[1] += strlen(_PATH_DEV);
160 if (utmp_chk(argv[0], argv[1]))
161 errx(1, "%s is not logged in on %s", argv[0], argv[1]);
162 if (term_chk(devfd, argv[1], &msgsok, &atime, 1))
163 exit(1);
164 if (myuid && !msgsok)
165 errx(1, "%s has messages disabled on %s", argv[0], argv[1]);
166 do_write(devfd, argv[1], mytty, login);
167 break;
168 default:
169 usage();
170 }
171 done(0);
172 return (0);
173 }
174
175 static void
usage(void)176 usage(void)
177 {
178 (void)fprintf(stderr, "usage: write user [tty]\n");
179 exit(1);
180 }
181
182 /*
183 * utmp_chk - checks that the given user is actually logged in on
184 * the given tty
185 */
186 int
utmp_chk(char * user,char * tty)187 utmp_chk(char *user, char *tty)
188 {
189 struct utmpx lu, *u;
190
191 strncpy(lu.ut_line, tty, sizeof lu.ut_line);
192 while ((u = getutxline(&lu)) != NULL)
193 if (u->ut_type == USER_PROCESS &&
194 strcmp(user, u->ut_user) == 0) {
195 endutxent();
196 return(0);
197 }
198 endutxent();
199 return(1);
200 }
201
202 /*
203 * search_utmp - search utmp for the "best" terminal to write to
204 *
205 * Ignores terminals with messages disabled, and of the rest, returns
206 * the one with the most recent access time. Returns as value the number
207 * of the user's terminals with messages enabled, or -1 if the user is
208 * not logged in at all.
209 *
210 * Special case for writing to yourself - ignore the terminal you're
211 * writing from, unless that's the only terminal with messages enabled.
212 */
213 void
search_utmp(int devfd,char * user,char * tty,char * mytty,uid_t myuid)214 search_utmp(int devfd, char *user, char *tty, char *mytty, uid_t myuid)
215 {
216 struct utmpx *u;
217 time_t bestatime, atime;
218 int nloggedttys, nttys, msgsok, user_is_me;
219
220 nloggedttys = nttys = 0;
221 bestatime = 0;
222 user_is_me = 0;
223
224 while ((u = getutxent()) != NULL)
225 if (u->ut_type == USER_PROCESS &&
226 strcmp(user, u->ut_user) == 0) {
227 ++nloggedttys;
228 if (term_chk(devfd, u->ut_line, &msgsok, &atime, 0))
229 continue; /* bad term? skip */
230 if (myuid && !msgsok)
231 continue; /* skip ttys with msgs off */
232 if (strcmp(u->ut_line, mytty) == 0) {
233 user_is_me = 1;
234 continue; /* don't write to yourself */
235 }
236 ++nttys;
237 if (atime > bestatime) {
238 bestatime = atime;
239 (void)strlcpy(tty, u->ut_line, MAXPATHLEN);
240 }
241 }
242 endutxent();
243
244 if (nloggedttys == 0)
245 errx(1, "%s is not logged in", user);
246 if (nttys == 0) {
247 if (user_is_me) { /* ok, so write to yourself! */
248 (void)strlcpy(tty, mytty, MAXPATHLEN);
249 return;
250 }
251 errx(1, "%s has messages disabled", user);
252 } else if (nttys > 1) {
253 warnx("%s is logged in more than once; writing to %s", user, tty);
254 }
255 }
256
257 /*
258 * term_chk - check that a terminal exists, and get the message bit
259 * and the access time
260 */
261 int
term_chk(int devfd,char * tty,int * msgsokP,time_t * atimeP,int showerror)262 term_chk(int devfd, char *tty, int *msgsokP, time_t *atimeP, int showerror)
263 {
264 struct stat s;
265
266 if (fstatat(devfd, tty, &s, 0) < 0) {
267 if (showerror)
268 warn("%s%s", _PATH_DEV, tty);
269 return(1);
270 }
271 *msgsokP = (s.st_mode & (S_IWRITE >> 3)) != 0; /* group write bit */
272 *atimeP = s.st_atime;
273 return(0);
274 }
275
276 /*
277 * do_write - actually make the connection
278 */
279 void
do_write(int devfd,char * tty,char * mytty,const char * login)280 do_write(int devfd, char *tty, char *mytty, const char *login)
281 {
282 char *nows;
283 time_t now;
284 char host[MAXHOSTNAMELEN];
285 wchar_t line[512];
286 int fd;
287
288 fd = openat(devfd, tty, O_WRONLY);
289 if (fd < 0)
290 err(1, "openat(%s%s)", _PATH_DEV, tty);
291 fclose(stdout);
292 stdout = fdopen(fd, "w");
293 if (stdout == NULL)
294 err(1, "%s%s", _PATH_DEV, tty);
295
296 (void)signal(SIGINT, done);
297 (void)signal(SIGHUP, done);
298
299 /* print greeting */
300 if (gethostname(host, sizeof(host)) < 0)
301 (void)strcpy(host, "???");
302 now = time((time_t *)NULL);
303 nows = ctime(&now);
304 nows[16] = '\0';
305 (void)printf("\r\n\007\007\007Message from %s@%s on %s at %s ...\r\n",
306 login, host, mytty, nows + 11);
307
308 while (fgetws(line, sizeof(line)/sizeof(wchar_t), stdin) != NULL)
309 wr_fputs(line);
310 }
311
312 /*
313 * done - cleanup and exit
314 */
315 void
done(int n __unused)316 done(int n __unused)
317 {
318 (void)printf("EOF\r\n");
319 exit(0);
320 }
321
322 /*
323 * wr_fputs - like fputs(), but makes control characters visible and
324 * turns \n into \r\n
325 */
326 void
wr_fputs(wchar_t * s)327 wr_fputs(wchar_t *s)
328 {
329
330 #define PUTC(c) if (putwchar(c) == WEOF) err(1, NULL);
331
332 for (; *s != L'\0'; ++s) {
333 if (*s == L'\n') {
334 PUTC(L'\r');
335 PUTC(L'\n');
336 } else if (iswprint(*s) || iswspace(*s)) {
337 PUTC(*s);
338 } else {
339 wprintf(L"<0x%X>", *s);
340 }
341 }
342 return;
343 #undef PUTC
344 }
345