usr.bin/write/write.c

   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  * @(#) Copyright (c) 1989, 1993 The Regents of the University of California.  All rights reserved.
  37  * @(#)write.c  8.1 (Berkeley) 6/6/93
  38  * $FreeBSD: src/usr.bin/write/write.c,v 1.12 1999/08/28 01:07:48 peter Exp $
  39  * $DragonFly: src/usr.bin/write/write.c,v 1.7 2005/08/30 22:02:36 liamfoy Exp $
  40  */
  41
  42 #include <sys/param.h>
  43 #include <sys/stat.h>
  44 #include <sys/file.h>
  45
  46 #include <ctype.h>
  47 #include <err.h>
  48 #include <locale.h>
  49 #include <paths.h>
  50 #include <pwd.h>
  51 #include <stdio.h>
  52 #include <stdlib.h>
  53 #include <string.h>
  54 #include <signal.h>
  55 #include <time.h>
  56 #include <unistd.h>
  57 #include <utmp.h>
  58
  59 static void     done(int);
  60 static void     do_write(const char *, const char *, uid_t, int *);
  61 static void     usage(void);
  62 static int      term_chk(const char *, int *, time_t *, int);
  63 static void     wr_fputs(unsigned char *s);
  64 static void     search_utmp(const char *, char *, size_t, const char *, uid_t);
  65 static int      utmp_chk(const char *, const char *);
  66
  67 int
  68 main(int argc, char **argv)
  69 {
  70         time_t atime;
  71         uid_t myuid;
  72         int msgsok, mymsgok, myttyfd;
  73         char tty[MAXPATHLEN], *mytty;
  74
  75         setlocale(LC_CTYPE, "");
  76
  77         /* check that sender has write enabled */
  78         if (isatty(fileno(stdin)))
  79                 myttyfd = fileno(stdin);
  80         else if (isatty(fileno(stdout)))
  81                 myttyfd = fileno(stdout);
  82         else if (isatty(fileno(stderr)))
  83                 myttyfd = fileno(stderr);
  84         else
  85                 errx(1, "can't find your tty");
  86         if (!(mytty = ttyname(myttyfd)))
  87                 errx(1, "can't find your tty's name");
  88         if (!strncmp(mytty, _PATH_DEV, strlen(_PATH_DEV)))
  89                 mytty += strlen(_PATH_DEV);
  90         if (term_chk(mytty, &mymsgok, &atime, 1))
  91                 exit(1);
  92         if (!mymsgok)
  93                 warnx("you have write permission turned off (man mesg)");
  94
  95         myuid = getuid();
  96
  97         /* check args */
  98         switch (argc) {
  99         case 2:
 100                 search_utmp(argv[1], tty, sizeof tty, mytty, myuid);
 101                 do_write(tty, mytty, myuid, &mymsgok);
 102                 break;
 103         case 3:
 104                 if (!strncmp(argv[2], _PATH_DEV, strlen(_PATH_DEV)))
 105                         argv[2] += strlen(_PATH_DEV);
 106                 if (utmp_chk(argv[1], argv[2]))
 107                         errx(1, "%s is not logged in on %s", argv[1], argv[2]);
 108                 if (term_chk(argv[2], &msgsok, &atime, 1))
 109                         exit(1);
 110                 if (myuid && !msgsok)
 111                         errx(1, "%s has messages disabled on %s", argv[1], argv[2]);
 112                 do_write(argv[2], mytty, myuid, &mymsgok);
 113                 break;
 114         default:
 115                 usage();
 116         }
 117         done(0);
 118         return (0);
 119 }
 120
 121 static void
 122 usage(void)
 123 {
 124         fprintf(stderr, "usage: write user [tty]\n");
 125         exit(1);
 126 }
 127
 128 /*
 129  * utmp_chk - checks that the given user is actually logged in on
 130  *     the given tty
 131  */
 132 static int
 133 utmp_chk(const char *user, const char *tty)
 134 {
 135         struct utmp u;
 136         int ufd;
 137
 138         if ((ufd = open(_PATH_UTMP, O_RDONLY)) < 0)
 139                 err(1, "open failed: %s\n", _PATH_UTMP);
 140
 141         while (read(ufd, (char *) &u, sizeof(u)) == sizeof(u)) {
 142                 if (strncmp(user, u.ut_name, sizeof(u.ut_name)) == 0 &&
 143                     strncmp(tty, u.ut_line, sizeof(u.ut_line)) == 0) {
 144                         close(ufd);
 145                         return(0);
 146                 }
 147         }
 148
 149         close(ufd);
 150         return(1);
 151 }
 152
 153 /*
 154  * search_utmp - search utmp for the "best" terminal to write to
 155  *
 156  * Ignores terminals with messages disabled, and of the rest, returns
 157  * the one with the most recent access time.  Returns as value the number
 158  * of the user's terminals with messages enabled, or -1 if the user is
 159  * not logged in at all.
 160  *
 161  * Special case for writing to yourself - ignore the terminal you're
 162  * writing from, unless that's the only terminal with messages enabled.
 163  */
 164 static void
 165 search_utmp(const char *user, char *tty, size_t ttyl, const char *mytty, uid_t myuid)
 166 {
 167         struct utmp u;
 168         time_t bestatime, atime;
 169         int ufd, nloggedttys, nttys, msgsok, user_is_me;
 170         char atty[UT_LINESIZE + 1];
 171
 172         if ((ufd = open(_PATH_UTMP, O_RDONLY)) < 0)
 173                 err(1, "open failed: %s", _PATH_UTMP);
 174
 175         nloggedttys = nttys = 0;
 176         bestatime = 0;
 177         user_is_me = 0;
 178         while (read(ufd, (char *) &u, sizeof(u)) == sizeof(u))
 179                 if (strncmp(user, u.ut_name, sizeof(u.ut_name)) == 0) {
 180                         ++nloggedttys;
 181                         strlcpy(atty, u.ut_line, ttyl);
 182                         if (term_chk(atty, &msgsok, &atime, 0))
 183                                 continue;       /* bad term? skip */
 184                         if (myuid && !msgsok)
 185                                 continue;       /* skip ttys with msgs off */
 186                         if (strcmp(atty, mytty) == 0) {
 187                                 user_is_me = 1;
 188                                 continue;       /* don't write to yourself */
 189                         }
 190                         ++nttys;
 191                         if (atime > bestatime) {
 192                                 bestatime = atime;
 193                                 strlcpy(tty, atty, ttyl);
 194                         }
 195                 }
 196
 197         close(ufd);
 198         if (nloggedttys == 0)
 199                 errx(1, "%s is not logged in", user);
 200         if (nttys == 0) {
 201                 if (user_is_me) {               /* ok, so write to yourself! */
 202                         strlcpy(tty, mytty, ttyl);
 203                         return;
 204                 }
 205                 errx(1, "%s has messages disabled", user);
 206         } else if (nttys > 1) {
 207                 warnx("%s is logged in more than once; writing to %s", user, tty);
 208         }
 209 }
 210
 211 /*
 212  * term_chk - check that a terminal exists, and get the message bit
 213  *     and the access time
 214  */
 215 static int
 216 term_chk(const char *tty, int *msgsokP, time_t *atimeP, int showerror)
 217 {
 218         struct stat s;
 219         char path[MAXPATHLEN];
 220
 221         snprintf(path, sizeof(path), "%s%s", _PATH_DEV, tty);
 222         if (stat(path, &s) < 0) {
 223                 if (showerror)
 224                         warn("%s", path);
 225                 return(1);
 226         }
 227         *msgsokP = (s.st_mode & S_IWGRP) != 0;  /* group write bit */
 228         *atimeP = s.st_atime;
 229         return(0);
 230 }
 231
 232 /*
 233  * do_write - actually make the connection
 234  */
 235 static void
 236 do_write(const char *tty, const char *mytty, uid_t myuid, int *mymsgok)
 237 {
 238         const char *login;
 239         char *nows;
 240         struct passwd *pwd;
 241         time_t now;
 242         char path[MAXPATHLEN], host[MAXHOSTNAMELEN], line[512];
 243
 244         /* Determine our login name before we reopen() stdout */
 245         if ((login = getlogin()) == NULL) {
 246                 if ((pwd = getpwuid(myuid)))
 247                         login = pwd->pw_name;
 248                 else
 249                         login = "???";
 250         }
 251
 252         snprintf(path, sizeof(path), "%s%s", _PATH_DEV, tty);
 253         if ((freopen(path, "w", stdout)) == NULL)
 254                 err(1, "%s", path);
 255
 256         signal(SIGINT, done);
 257         signal(SIGHUP, done);
 258
 259         /* print greeting */
 260         if (gethostname(host, sizeof(host)) < 0)
 261                 strlcpy(host, "???", sizeof host);
 262         now = time(NULL);
 263         nows = ctime(&now);
 264         nows[16] = '\0';
 265         printf("\r\n\007\007\007Message from %s@%s on %s at %s (%s %s replies)...\r\n",
 266             login, host, mytty, nows + 11, login, *mymsgok == 0 ? "does not accept" : "accepts");
 267
 268         while (fgets(line, sizeof(line), stdin) != NULL)
 269                 wr_fputs(line);
 270 }
 271
 272 /*
 273  * done - cleanup and exit
 274  */
 275 static void
 276 done(__unused int n)
 277 {
 278         printf("EOF\r\n");
 279         exit(0);
 280 }
 281
 282 /*
 283  * wr_fputs - like fputs(), but makes control characters visible and
 284  *     turns \n into \r\n
 285  */
 286 static void
 287 wr_fputs(unsigned char *s)
 288 {
 289
 290 #define PUTC(c) if (putchar(c) == EOF) err(1, NULL);
 291
 292         for (; *s != '\0'; ++s) {
 293                 if (*s == '\n') {
 294                         PUTC('\r');
 295                 } else if (((*s & 0x80) && *s < 0xA0) ||
 296                            /* disable upper controls */
 297                            (!isprint(*s) && !isspace(*s) &&
 298                             *s != '\a' && *s != '\b')
 299                           ) {
 300                         if (*s & 0x80) {
 301                                 *s &= ~0x80;
 302                                 PUTC('M');
 303                                 PUTC('-');
 304                         }
 305                         if (iscntrl(*s)) {
 306                                 *s ^= 0x40;
 307                                 PUTC('^');
 308                         }
 309                 }
 310                 PUTC(*s);
 311         }
 312         return;
 313 #undef PUTC
 314 }