/*      $OpenBSD: ttymsg.c,v 1.21 2023/05/02 09:51:22 tb Exp $  */
/*      $NetBSD: ttymsg.c,v 1.3 1994/11/17 07:17:55 jtc Exp $   */

/*
 * Copyright (c) 1989, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/types.h>
#include <sys/stat.h>
#include <sys/uio.h>
#include <signal.h>
#include <fcntl.h>
#include <dirent.h>
#include <errno.h>
#include <paths.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <err.h>

char *ttymsg(struct iovec *, int, char *, int);

/*
 * Display the contents of a uio structure on a terminal.  Used by wall(1)
 * and talkd(8).  Forks and finishes in child if write would block,
 * waiting up to tmout seconds.  Returns pointer to error string on unexpected
 * error; string is not newline-terminated.  Various "normal" errors are
 * ignored (exclusive-use, lack of permission, etc.).
 */
char *
ttymsg(struct iovec *iov, int iovcnt, char *line, int tmout)
{
        static char device[MAXNAMLEN] = _PATH_DEV;
        static char errbuf[1024];
        int cnt, fd, left, wret;
        struct iovec localiov[6];
        int forked = 0;
        struct stat st;
        sigset_t mask;

        if (iovcnt > sizeof(localiov) / sizeof(localiov[0]))
                return ("too many iov's (change code in wall/ttymsg.c)");

        /*
         * Ignore lines that start with "ftp" or "uucp".
         */
        if ((strncmp(line, "ftp", 3) == 0) ||
            (strncmp(line, "uucp", 4) == 0))
                return (NULL);

        (void) strlcpy(device + sizeof(_PATH_DEV) - 1, line,
            sizeof(device) - (sizeof(_PATH_DEV) - 1));
        if (strchr(device + sizeof(_PATH_DEV) - 1, '/')) {
                /* A slash is an attempt to break security... */
                (void) snprintf(errbuf, sizeof(errbuf), "'/' in \"%s\"",
                    device);
                return (errbuf);
        }

        /*
         * open will fail on slip lines or exclusive-use lines
         * if not running as root; not an error.
         */
        if ((fd = open(device, O_WRONLY|O_NONBLOCK)) == -1) {
                if (errno == EBUSY || errno == EACCES)
                        return (NULL);
                (void) snprintf(errbuf, sizeof(errbuf),
                    "%s: %s", device, strerror(errno));
                return (errbuf);
        }

        if (getuid()) {
                if (fstat(fd, &st) == -1 ||
                    (st.st_mode & S_IWGRP) == 0) {
                        close(fd);
                        return (NULL);
                }
        }

        for (cnt = left = 0; cnt < iovcnt; ++cnt)
                left += iov[cnt].iov_len;

        for (;;) {
                wret = writev(fd, iov, iovcnt);
                if (wret >= left)
                        break;
                if (wret >= 0) {
                        left -= wret;
                        if (iov != localiov) {
                                bcopy(iov, localiov,
                                    iovcnt * sizeof(struct iovec));
                                iov = localiov;
                        }
                        for (cnt = 0; wret >= iov->iov_len; ++cnt) {
                                wret -= iov->iov_len;
                                ++iov;
                                --iovcnt;
                        }
                        if (wret) {
                                char *base = iov->iov_base;

                                iov->iov_base = base + wret;
                                iov->iov_len -= wret;
                        }
                        continue;
                }
                if (errno == EWOULDBLOCK) {
                        int off = 0;
                        pid_t cpid;

                        if (forked) {
                                (void) close(fd);
                                _exit(1);
                        }
                        cpid = fork();
                        if (cpid == -1) {
                                (void) snprintf(errbuf, sizeof(errbuf),
                                    "fork: %s", strerror(errno));
                                (void) close(fd);
                                return (errbuf);
                        }
                        if (cpid) {     /* parent */
                                (void) close(fd);
                                return (NULL);
                        }

                        if (pledge("stdio", NULL) == -1)
                                err(1, "pledge");

                        forked++;
                        /* wait at most tmout seconds */
                        (void) signal(SIGALRM, SIG_DFL);
                        (void) signal(SIGTERM, SIG_DFL); /* XXX */
                        (void) sigemptyset(&mask);
                        (void) sigprocmask(SIG_SETMASK, &mask, NULL);
                        (void) alarm((u_int)tmout);
                        (void) fcntl(fd, O_NONBLOCK, &off);
                        continue;
                }
                /*
                 * We get ENODEV on a slip line if we're running as root,
                 * and EIO if the line just went away.
                 */
                if (errno == ENODEV || errno == EIO)
                        break;
                (void) close(fd);
                if (forked)
                        _exit(1);
                (void) snprintf(errbuf, sizeof(errbuf),
                    "%s: %s", device, strerror(errno));
                return (errbuf);
        }

        (void) close(fd);
        if (forked)
                _exit(0);
        return (NULL);
}