usr.bin/write/term_chk.c

   1 /* $NetBSD: term_chk.c,v 1.8 2009/04/14 07:59:17 lukem Exp $ */
   2
   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/cdefs.h>
  36 #ifndef lint
  37 __RCSID("$NetBSD: term_chk.c,v 1.8 2009/04/14 07:59:17 lukem Exp $");
  38 #endif
  39
  40 #include <sys/types.h>
  41 #include <sys/param.h>
  42 #include <sys/stat.h>
  43 #include <time.h>
  44 #include <stdio.h>
  45 #include <errno.h>
  46 #include <unistd.h>
  47 #include <paths.h>
  48 #include <fcntl.h>
  49 #include <string.h>
  50 #include <err.h>
  51
  52 #include "term_chk.h"
  53
  54 /*
  55  * term_chk - check that a terminal exists, and get the message bit
  56  *     and the access time
  57  */
  58 int
  59 term_chk(uid_t uid, const char *tty, int *msgsokP, time_t *atimeP, int ismytty,
  60     gid_t saved_egid)
  61 {
  62         char path[MAXPATHLEN];
  63         struct stat s;
  64         int i, fd, serrno;
  65
  66         if (strstr(tty, "../") != NULL) {
  67                 errno = EINVAL;
  68                 return -1;
  69         }
  70         i = snprintf(path, sizeof path, _PATH_DEV "%s", tty);
  71         if (i < 0 || i >= (int)sizeof(path)) {
  72                 errno = ENOMEM;
  73                 return -1;
  74         }
  75
  76         (void)setegid(saved_egid);
  77         fd = open(path, O_WRONLY, 0);
  78         serrno = errno;
  79         (void)setegid(getgid());
  80         errno = serrno;
  81
  82         if (fd == -1)
  83                 return(-1);
  84         if (fstat(fd, &s) == -1)
  85                 goto error;
  86         if (!isatty(fd))
  87                 goto error;
  88         if (s.st_uid != uid && uid != 0) {
  89                 errno = EPERM;
  90                 goto error;
  91         }
  92         if (msgsokP)
  93                 *msgsokP = (s.st_mode & S_IWGRP) != 0;  /* group write bit */
  94         if (atimeP)
  95                 *atimeP = s.st_atime;
  96         if (ismytty)
  97                 (void)close(fd);
  98         return ismytty ? 0 : fd;
  99 error:
 100         if (fd != -1) {
 101                 serrno = errno;
 102                 (void)close(fd);
 103                 errno = serrno;
 104         }
 105         return -1;
 106 }
 107
 108 char *
 109 check_sender(time_t *atime, uid_t myuid, gid_t saved_egid)
 110 {
 111         int myttyfd;
 112         int msgsok;
 113         char *mytty;
 114
 115         /* check that sender has write enabled */
 116         if (isatty(fileno(stdin)))
 117                 myttyfd = fileno(stdin);
 118         else if (isatty(fileno(stdout)))
 119                 myttyfd = fileno(stdout);
 120         else if (isatty(fileno(stderr)))
 121                 myttyfd = fileno(stderr);
 122         else if (atime == NULL)
 123                 return NULL;
 124         else
 125                 errx(1, "Cannot find your tty");
 126         if ((mytty = ttyname(myttyfd)) == NULL)
 127                 err(1, "Cannot find the name of your tty");
 128         if (strncmp(mytty, _PATH_DEV, sizeof(_PATH_DEV) - 1) == 0)
 129                 mytty += sizeof(_PATH_DEV) - 1;
 130         if (term_chk(myuid, mytty, &msgsok, atime, 1, saved_egid) == -1)
 131                 err(1, "%s%s", _PATH_DEV, mytty);
 132         if (!msgsok) {
 133                 warnx(
 134                     "You have write permission turned off; no reply possible");
 135         }
 136         return mytty;
 137 }