1 /* $OpenBSD: write.c,v 1.17 2002/08/04 01:26:40 deraadt Exp $ */ 2 /* $NetBSD: write.c,v 1.5 1995/08/31 21:48:32 jtc Exp $ */ 3 4 /* 5 * Copyright (c) 1989, 1993 6 * The Regents of the University of California. All rights reserved. 7 * 8 * This code is derived from software contributed to Berkeley by 9 * Jef Poskanzer and Craig Leres of the Lawrence Berkeley Laboratory. 10 * 11 * Redistribution and use in source and binary forms, with or without 12 * modification, are permitted provided that the following conditions 13 * are met: 14 * 1. Redistributions of source code must retain the above copyright 15 * notice, this list of conditions and the following disclaimer. 16 * 2. Redistributions in binary form must reproduce the above copyright 17 * notice, this list of conditions and the following disclaimer in the 18 * documentation and/or other materials provided with the distribution. 19 * 3. All advertising materials mentioning features or use of this software 20 * must display the following acknowledgement: 21 * This product includes software developed by the University of 22 * California, Berkeley and its contributors. 23 * 4. Neither the name of the University nor the names of its contributors 24 * may be used to endorse or promote products derived from this software 25 * without specific prior written permission. 26 * 27 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 28 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 29 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 30 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 31 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 32 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 33 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 34 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 35 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 36 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 37 * SUCH DAMAGE. 38 */ 39 40 #ifndef lint 41 static char copyright[] = 42 "@(#) Copyright (c) 1989, 1993\n\ 43 The Regents of the University of California. All rights reserved.\n"; 44 #endif /* not lint */ 45 46 #ifndef lint 47 #if 0 48 static char sccsid[] = "@(#)write.c 8.2 (Berkeley) 4/27/95"; 49 #endif 50 static char *rcsid = "$OpenBSD: write.c,v 1.17 2002/08/04 01:26:40 deraadt Exp $"; 51 #endif /* not lint */ 52 53 #include <sys/types.h> 54 #include <sys/param.h> 55 #include <sys/stat.h> 56 #include <ctype.h> 57 #include <stdio.h> 58 #include <string.h> 59 #include <signal.h> 60 #include <time.h> 61 #include <fcntl.h> 62 #include <paths.h> 63 #include <pwd.h> 64 #include <unistd.h> 65 #include <utmp.h> 66 #include <err.h> 67 #include <vis.h> 68 69 void done(int sig); 70 void do_write(char *, char *, uid_t); 71 void wr_fputs(char *); 72 void search_utmp(char *, char *, char *, uid_t); 73 int term_chk(char *, int *, time_t *, int); 74 int utmp_chk(char *, char *); 75 76 int 77 main(int argc, char **argv) 78 { 79 char tty[MAXPATHLEN], *mytty, *cp; 80 int msgsok, myttyfd; 81 time_t atime; 82 uid_t myuid; 83 84 /* check that sender has write enabled */ 85 if (isatty(fileno(stdin))) 86 myttyfd = fileno(stdin); 87 else if (isatty(fileno(stdout))) 88 myttyfd = fileno(stdout); 89 else if (isatty(fileno(stderr))) 90 myttyfd = fileno(stderr); 91 else 92 errx(1, "can't find your tty"); 93 if (!(mytty = ttyname(myttyfd))) 94 errx(1, "can't find your tty's name"); 95 if ((cp = strrchr(mytty, '/'))) 96 mytty = cp + 1; 97 if (term_chk(mytty, &msgsok, &atime, 1)) 98 exit(1); 99 if (!msgsok) 100 warnx("you have write permission turned off"); 101 102 myuid = getuid(); 103 104 /* check args */ 105 switch (argc) { 106 case 2: 107 search_utmp(argv[1], tty, mytty, myuid); 108 do_write(tty, mytty, myuid); 109 break; 110 case 3: 111 if (!strncmp(argv[2], _PATH_DEV, sizeof(_PATH_DEV) - 1)) 112 argv[2] += sizeof(_PATH_DEV) - 1; 113 if (utmp_chk(argv[1], argv[2])) 114 errx(1, "%s is not logged in on %s", 115 argv[1], argv[2]); 116 if (term_chk(argv[2], &msgsok, &atime, 1)) 117 exit(1); 118 if (myuid && !msgsok) 119 errx(1, "%s has messages disabled on %s", 120 argv[1], argv[2]); 121 do_write(argv[2], mytty, myuid); 122 break; 123 default: 124 (void)fprintf(stderr, "usage: write user [tty]\n"); 125 exit(1); 126 } 127 done(0); 128 129 /* NOTREACHED */ 130 return (0); 131 } 132 133 /* 134 * utmp_chk - checks that the given user is actually logged in on 135 * the given tty 136 */ 137 int 138 utmp_chk(char *user, char *tty) 139 { 140 struct utmp u; 141 int ufd; 142 143 if ((ufd = open(_PATH_UTMP, O_RDONLY)) < 0) 144 return(0); /* ignore error, shouldn't happen anyway */ 145 146 while (read(ufd, (char *) &u, sizeof(u)) == sizeof(u)) 147 if (strncmp(user, u.ut_name, sizeof(u.ut_name)) == 0 && 148 strncmp(tty, u.ut_line, sizeof(u.ut_line)) == 0) { 149 (void)close(ufd); 150 return(0); 151 } 152 153 (void)close(ufd); 154 return(1); 155 } 156 157 /* 158 * search_utmp - search utmp for the "best" terminal to write to 159 * 160 * Ignores terminals with messages disabled, and of the rest, returns 161 * the one with the most recent access time. Returns as value the number 162 * of the user's terminals with messages enabled, or -1 if the user is 163 * not logged in at all. 164 * 165 * Special case for writing to yourself - ignore the terminal you're 166 * writing from, unless that's the only terminal with messages enabled. 167 */ 168 void 169 search_utmp(char *user, char *tty, char *mytty, uid_t myuid) 170 { 171 struct utmp u; 172 time_t bestatime, atime; 173 int ufd, nloggedttys, nttys, msgsok, user_is_me; 174 char atty[UT_LINESIZE + 1]; 175 176 if ((ufd = open(_PATH_UTMP, O_RDONLY)) < 0) 177 err(1, "%s", _PATH_UTMP); 178 179 nloggedttys = nttys = 0; 180 bestatime = 0; 181 user_is_me = 0; 182 while (read(ufd, (char *) &u, sizeof(u)) == sizeof(u)) 183 if (strncmp(user, u.ut_name, sizeof(u.ut_name)) == 0) { 184 ++nloggedttys; 185 (void)strncpy(atty, u.ut_line, UT_LINESIZE); 186 atty[UT_LINESIZE] = '\0'; 187 if (term_chk(atty, &msgsok, &atime, 0)) 188 continue; /* bad term? skip */ 189 if (myuid && !msgsok) 190 continue; /* skip ttys with msgs off */ 191 if (strcmp(atty, mytty) == 0) { 192 user_is_me = 1; 193 continue; /* don't write to yourself */ 194 } 195 ++nttys; 196 if (atime > bestatime) { 197 bestatime = atime; 198 (void)strcpy(tty, atty); 199 } 200 } 201 202 (void)close(ufd); 203 if (nloggedttys == 0) 204 errx(1, "%s is not logged in", user); 205 if (nttys == 0) { 206 if (user_is_me) { /* ok, so write to yourself! */ 207 (void)strcpy(tty, mytty); 208 return; 209 } 210 errx(1, "%s has messages disabled", user); 211 } else if (nttys > 1) 212 warnx("%s is logged in more than once; writing to %s", 213 user, tty); 214 } 215 216 /* 217 * term_chk - check that a terminal exists, and get the message bit 218 * and the access time 219 */ 220 int 221 term_chk(char *tty, int *msgsokP, time_t *atimeP, int showerror) 222 { 223 struct stat s; 224 char path[MAXPATHLEN]; 225 226 (void)snprintf(path, sizeof(path), "%s%s", _PATH_DEV, tty); 227 if (stat(path, &s) < 0) { 228 if (showerror) 229 warn("%s", path); 230 return(1); 231 } 232 *msgsokP = (s.st_mode & S_IWGRP) != 0; /* group write bit */ 233 *atimeP = s.st_atime; 234 return(0); 235 } 236 237 /* 238 * do_write - actually make the connection 239 */ 240 void 241 do_write(char *tty, char *mytty, uid_t myuid) 242 { 243 char *login, *nows; 244 struct passwd *pwd; 245 time_t now; 246 char path[MAXPATHLEN], host[MAXHOSTNAMELEN], line[512]; 247 248 /* Determine our login name before the we reopen() stdout */ 249 if ((login = getlogin()) == NULL) { 250 if ((pwd = getpwuid(myuid))) 251 login = pwd->pw_name; 252 else 253 login = "???"; 254 } 255 256 (void)snprintf(path, sizeof(path), "%s%s", _PATH_DEV, tty); 257 if ((freopen(path, "w", stdout)) == NULL) 258 err(1, "%s", path); 259 260 /* revoke privs, now that we have opened the tty */ 261 setegid(getgid()); 262 setgid(getgid()); 263 264 (void)signal(SIGINT, done); 265 (void)signal(SIGHUP, done); 266 267 /* print greeting */ 268 if (gethostname(host, sizeof(host)) < 0) 269 (void)strcpy(host, "???"); 270 now = time((time_t *)NULL); 271 nows = ctime(&now); 272 nows[16] = '\0'; 273 (void)printf("\r\n\007\007\007Message from %s@%s on %s at %s ...\r\n", 274 login, host, mytty, nows + 11); 275 276 while (fgets(line, sizeof(line), stdin) != NULL) 277 wr_fputs(line); 278 } 279 280 /* 281 * done - cleanup and exit 282 */ 283 void 284 done(int sig) 285 { 286 (void)write(STDOUT_FILENO, "EOF\r\n", 5); 287 if (sig) 288 _exit(0); 289 else 290 exit(0); 291 } 292 293 /* 294 * wr_fputs - like fputs(), but makes control characters visible and 295 * turns \n into \r\n 296 */ 297 void 298 wr_fputs(char *s) 299 { 300 u_char c; 301 char visout[5], *s2; 302 303 #define PUTC(c) if (putchar(c) == EOF) goto err; 304 305 for (; *s != '\0'; ++s) { 306 c = toascii(*s); 307 if (c == '\n') { 308 PUTC('\r'); 309 PUTC('\n'); 310 continue; 311 } 312 vis(visout, c, VIS_SAFE|VIS_NOSLASH, s[1]); 313 for (s2 = visout; *s2; s2++) 314 PUTC(*s2); 315 } 316 return; 317 318 err: err(1, NULL); 319 #undef PUTC 320 } 321