/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 1989, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Jef Poskanzer and Craig Leres of the Lawrence Berkeley Laboratory.
 *
 * 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/param.h>
#include <sys/capsicum.h>
#include <sys/filio.h>
#include <sys/signal.h>
#include <sys/stat.h>
#include <sys/time.h>

#include <capsicum_helpers.h>
#include <ctype.h>
#include <err.h>
#include <errno.h>
#include <locale.h>
#include <paths.h>
#include <pwd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <utmpx.h>
#include <wchar.h>
#include <wctype.h>

void done(int);
void do_write(int, char *, char *, const char *);
static void usage(void) __dead2;
int term_chk(int, char *, int *, time_t *, int);
void wr_fputs(wchar_t *s);
void search_utmp(int, char *, char *, char *, uid_t);
int utmp_chk(char *, char *);

int
main(int argc, char **argv)
{
        unsigned long cmds[] = { TIOCGETA, TIOCGWINSZ, FIODGNAME };
        cap_rights_t rights;
        struct passwd *pwd;
        time_t atime;
        uid_t myuid;
        int msgsok, myttyfd;
        char tty[MAXPATHLEN], *mytty;
        const char *login;
        int devfd;

        (void)setlocale(LC_CTYPE, "");

        devfd = open(_PATH_DEV, O_RDONLY);
        if (devfd < 0)
                err(1, "open(/dev)");
        cap_rights_init(&rights, CAP_FCNTL, CAP_FSTAT, CAP_IOCTL, CAP_LOOKUP,
            CAP_PWRITE);
        if (caph_rights_limit(devfd, &rights) < 0)
                err(1, "can't limit devfd rights");

        /*
         * Can't use capsicum helpers here because we need the additional
         * FIODGNAME ioctl.
         */
        cap_rights_init(&rights, CAP_FCNTL, CAP_FSTAT, CAP_IOCTL, CAP_READ,
            CAP_WRITE);
        if (caph_rights_limit(STDIN_FILENO, &rights) < 0 ||
            caph_rights_limit(STDOUT_FILENO, &rights) < 0 ||
            caph_rights_limit(STDERR_FILENO, &rights) < 0 ||
            caph_ioctls_limit(STDIN_FILENO, cmds, nitems(cmds)) < 0 ||
            caph_ioctls_limit(STDOUT_FILENO, cmds, nitems(cmds)) < 0 ||
            caph_ioctls_limit(STDERR_FILENO, cmds, nitems(cmds)) < 0 ||
            caph_fcntls_limit(STDIN_FILENO, CAP_FCNTL_GETFL) < 0 ||
            caph_fcntls_limit(STDOUT_FILENO, CAP_FCNTL_GETFL) < 0 ||
            caph_fcntls_limit(STDERR_FILENO, CAP_FCNTL_GETFL) < 0)
                err(1, "can't limit stdio rights");

        caph_cache_catpages();
        caph_cache_tzdata();

        /*
         * Cache UTX database fds.
         */
        setutxent();

        /*
         * Determine our login name before we reopen() stdout
         * and before entering capability sandbox.
         */
        myuid = getuid();
        if ((login = getlogin()) == NULL) {
                if ((pwd = getpwuid(myuid)))
                        login = pwd->pw_name;
                else
                        login = "???";
        }

        if (caph_enter() < 0)
                err(1, "cap_enter");

        while (getopt(argc, argv, "") != -1)
                usage();
        argc -= optind;
        argv += optind;

        /* check that sender has write enabled */
        if (isatty(fileno(stdin)))
                myttyfd = fileno(stdin);
        else if (isatty(fileno(stdout)))
                myttyfd = fileno(stdout);
        else if (isatty(fileno(stderr)))
                myttyfd = fileno(stderr);
        else
                errx(1, "can't find your tty");
        if (!(mytty = ttyname(myttyfd)))
                errx(1, "can't find your tty's name");
        if (!strncmp(mytty, _PATH_DEV, strlen(_PATH_DEV)))
                mytty += strlen(_PATH_DEV);
        if (term_chk(devfd, mytty, &msgsok, &atime, 1))
                exit(1);
        if (!msgsok)
                errx(1, "you have write permission turned off");

        /* check args */
        switch (argc) {
        case 1:
                search_utmp(devfd, argv[0], tty, mytty, myuid);
                do_write(devfd, tty, mytty, login);
                break;
        case 2:
                if (!strncmp(argv[1], _PATH_DEV, strlen(_PATH_DEV)))
                        argv[1] += strlen(_PATH_DEV);
                if (utmp_chk(argv[0], argv[1]))
                        errx(1, "%s is not logged in on %s", argv[0], argv[1]);
                if (term_chk(devfd, argv[1], &msgsok, &atime, 1))
                        exit(1);
                if (myuid && !msgsok)
                        errx(1, "%s has messages disabled on %s", argv[0], argv[1]);
                do_write(devfd, argv[1], mytty, login);
                break;
        default:
                usage();
        }
        done(0);
        return (0);
}

static void
usage(void)
{
        (void)fprintf(stderr, "usage: write user [tty]\n");
        exit(1);
}

/*
 * utmp_chk - checks that the given user is actually logged in on
 *     the given tty
 */
int
utmp_chk(char *user, char *tty)
{
        struct utmpx lu, *u;

        strncpy(lu.ut_line, tty, sizeof lu.ut_line);
        while ((u = getutxline(&lu)) != NULL)
                if (u->ut_type == USER_PROCESS &&
                    strcmp(user, u->ut_user) == 0) {
                        endutxent();
                        return(0);
                }
        endutxent();
        return(1);
}

/*
 * search_utmp - search utmp for the "best" terminal to write to
 *
 * Ignores terminals with messages disabled, and of the rest, returns
 * the one with the most recent access time.  Returns as value the number
 * of the user's terminals with messages enabled, or -1 if the user is
 * not logged in at all.
 *
 * Special case for writing to yourself - ignore the terminal you're
 * writing from, unless that's the only terminal with messages enabled.
 */
void
search_utmp(int devfd, char *user, char *tty, char *mytty, uid_t myuid)
{
        struct utmpx *u;
        time_t bestatime, atime;
        int nloggedttys, nttys, msgsok, user_is_me;

        nloggedttys = nttys = 0;
        bestatime = 0;
        user_is_me = 0;

        while ((u = getutxent()) != NULL)
                if (u->ut_type == USER_PROCESS &&
                    strcmp(user, u->ut_user) == 0) {
                        ++nloggedttys;
                        if (term_chk(devfd, u->ut_line, &msgsok, &atime, 0))
                                continue;       /* bad term? skip */
                        if (myuid && !msgsok)
                                continue;       /* skip ttys with msgs off */
                        if (strcmp(u->ut_line, mytty) == 0) {
                                user_is_me = 1;
                                continue;       /* don't write to yourself */
                        }
                        ++nttys;
                        if (atime > bestatime) {
                                bestatime = atime;
                                (void)strlcpy(tty, u->ut_line, MAXPATHLEN);
                        }
                }
        endutxent();

        if (nloggedttys == 0)
                errx(1, "%s is not logged in", user);
        if (nttys == 0) {
                if (user_is_me) {               /* ok, so write to yourself! */
                        (void)strlcpy(tty, mytty, MAXPATHLEN);
                        return;
                }
                errx(1, "%s has messages disabled", user);
        } else if (nttys > 1) {
                warnx("%s is logged in more than once; writing to %s", user, tty);
        }
}

/*
 * term_chk - check that a terminal exists, and get the message bit
 *     and the access time
 */
int
term_chk(int devfd, char *tty, int *msgsokP, time_t *atimeP, int showerror)
{
        struct stat s;

        if (fstatat(devfd, tty, &s, 0) < 0) {
                if (showerror)
                        warn("%s%s", _PATH_DEV, tty);
                return(1);
        }
        *msgsokP = (s.st_mode & (S_IWRITE >> 3)) != 0;  /* group write bit */
        *atimeP = s.st_atime;
        return(0);
}

/*
 * do_write - actually make the connection
 */
void
do_write(int devfd, char *tty, char *mytty, const char *login)
{
        char *nows;
        time_t now;
        char host[MAXHOSTNAMELEN];
        wchar_t line[512];
        int fd;

        fd = openat(devfd, tty, O_WRONLY);
        if (fd < 0)
                err(1, "openat(%s%s)", _PATH_DEV, tty);
        fclose(stdout);
        stdout = fdopen(fd, "w");
        if (stdout == NULL)
                err(1, "%s%s", _PATH_DEV, tty);

        (void)signal(SIGINT, done);
        (void)signal(SIGHUP, done);

        /* print greeting */
        if (gethostname(host, sizeof(host)) < 0)
                (void)strcpy(host, "???");
        now = time((time_t *)NULL);
        nows = ctime(&now);
        nows[16] = '\0';
        (void)printf("\r\n\007\007\007Message from %s@%s on %s at %s ...\r\n",
            login, host, mytty, nows + 11);

        while (fgetws(line, sizeof(line)/sizeof(wchar_t), stdin) != NULL)
                wr_fputs(line);
}

/*
 * done - cleanup and exit
 */
void
done(int n __unused)
{
        (void)printf("EOF\r\n");
        exit(0);
}

/*
 * wr_fputs - like fputs(), but makes control characters visible and
 *     turns \n into \r\n
 */
void
wr_fputs(wchar_t *s)
{

#define PUTC(c) if (putwchar(c) == WEOF) err(1, NULL);

        for (; *s != L'\0'; ++s) {
                if (*s == L'\n') {
                        PUTC(L'\r');
                        PUTC(L'\n');
                } else if (iswprint(*s) || iswspace(*s)) {
                        PUTC(*s);
                } else {
                        wprintf(L"<0x%X>", *s);
                }
        }
        return;
#undef PUTC
}