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term_chk.c revision 1.4 
      1 /* $NetBSD: term_chk.c,v 1.4 2003/08/07 11:17:48 agc 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 1.4 2003/08/07 11:17:48 agc 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 (strcspn(tty, "./") != strlen(tty)) {
     67 		errno = EINVAL;
     68 		return -1;
     69 	}
     70 	i = snprintf(path, sizeof path, _PATH_DEV "%s", tty);
     71 	if (i < 0 || i >= 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 	*msgsokP = (s.st_mode & S_IWGRP) != 0;	/* group write bit */
     93 	*atimeP = s.st_atime;
     94 	if (ismytty)
     95 		(void)close(fd);
     96 	return ismytty ? 0 : fd;
     97 error:
     98 	if (fd != -1) {
     99 		serrno = errno;
    100 		(void)close(fd);
    101 		errno = serrno;
    102 	}
    103 	return -1;
    104 }
    105 
    106 char *
    107 check_sender(time_t *atime, uid_t myuid, gid_t saved_egid)
    108 {
    109 	int myttyfd;
    110 	int msgsok;
    111 	char *mytty;
    112 	char *cp;
    113 
    114 	/* check that sender has write enabled */
    115 	if (isatty(fileno(stdin)))
    116 		myttyfd = fileno(stdin);
    117 	else if (isatty(fileno(stdout)))
    118 		myttyfd = fileno(stdout);
    119 	else if (isatty(fileno(stderr)))
    120 		myttyfd = fileno(stderr);
    121 	else
    122 		errx(1, "can't find your tty");
    123 	if (!(mytty = ttyname(myttyfd)))
    124 		errx(1, "can't find your tty's name");
    125 	if ((cp = strrchr(mytty, '/')) != NULL)
    126 		mytty = cp + 1;
    127 	if (term_chk(myuid, mytty, &msgsok, atime, 1, saved_egid) == -1)
    128 		err(1, "%s%s", _PATH_DEV, mytty);
    129 	if (!msgsok) {
    130 		warnx(
    131 		    "You have write permission turned off; no reply possible");
    132 	}
    133 	return mytty;
    134 }
    135