/*      $OpenBSD: comsat.c,v 1.51 2023/03/08 04:43:05 guenther Exp $    */

/*
 * Copyright (c) 1980, 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/limits.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/wait.h>

#include <netinet/in.h>

#include <ctype.h>
#include <errno.h>
#include <fcntl.h>
#include <netdb.h>
#include <limits.h>
#include <paths.h>
#include <pwd.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <syslog.h>
#include <termios.h>
#include <unistd.h>
#include <utmp.h>
#include <vis.h>
#include <err.h>

int     debug = 0;
#define dsyslog if (debug) syslog

#define MAXIDLE 120

char    hostname[HOST_NAME_MAX+1];
struct  utmp *utmp = NULL;
time_t  lastmsgtime;
int     nutmp, uf;

void jkfprintf(FILE *, char[], off_t);
void mailfor(char *);
void notify(struct utmp *, off_t);
void readutmp(int);
void doreadutmp(void);
void reapchildren(int);

volatile sig_atomic_t wantreadutmp;

int
main(int argc, char *argv[])
{
        struct sockaddr_storage from;
        struct sigaction sa;
        ssize_t cc;
        socklen_t fromlen;
        char msgbuf[100];
        sigset_t sigset;

        /* verify proper invocation */
        fromlen = sizeof(from);
        if (getsockname(0, (struct sockaddr *)&from, &fromlen) == -1) {
                (void)fprintf(stderr,
                    "comsat: getsockname: %s.\n", strerror(errno));
                exit(1);
        }

        if (unveil(_PATH_MAILDIR, "r") == -1)
                err(1, "unveil %s", _PATH_MAILDIR);
        if (unveil(_PATH_UTMP, "r") == -1)
                err(1, "unveil %s", _PATH_UTMP);
        if (unveil("/tmp", "w") == -1)
                err(1, "unveil /tmp");
        if (unveil(_PATH_DEV, "rw") == -1)
                err(1, "unveil %s", _PATH_DEV);
        if (pledge("stdio rpath wpath proc tty", NULL) == -1)
                err(1, "pledge");

        openlog("comsat", LOG_PID, LOG_DAEMON);
        if (chdir(_PATH_MAILDIR)) {
                syslog(LOG_ERR, "chdir: %s: %m", _PATH_MAILDIR);
                (void) recv(0, msgbuf, sizeof(msgbuf) - 1, 0);
                exit(1);
        }
        if ((uf = open(_PATH_UTMP, O_RDONLY)) == -1) {
                syslog(LOG_ERR, "open: %s: %m", _PATH_UTMP);
                (void) recv(0, msgbuf, sizeof(msgbuf) - 1, 0);
                exit(1);
        }
        (void)time(&lastmsgtime);
        (void)gethostname(hostname, sizeof(hostname));
        doreadutmp();

        (void)signal(SIGTTOU, SIG_IGN);

        bzero(&sa, sizeof sa);
        sigemptyset(&sa.sa_mask);
        sa.sa_handler = readutmp;
        sa.sa_flags = 0;                        /* no SA_RESTART */
        (void)sigaction(SIGALRM, &sa, NULL);

        sa.sa_handler = reapchildren;
        sa.sa_flags = SA_RESTART;
        (void)sigaction(SIGCHLD, &sa, NULL);

        for (;;) {
                if (wantreadutmp) {
                        wantreadutmp = 0;
                        doreadutmp();
                }

                cc = recv(0, msgbuf, sizeof(msgbuf) - 1, 0);
                if (cc <= 0) {
                        if (errno != EINTR)
                                sleep(1);
                        continue;
                }
                if (!nutmp)             /* no one has logged in yet */
                        continue;
                sigemptyset(&sigset);
                sigaddset(&sigset, SIGALRM);
                sigprocmask(SIG_SETMASK, &sigset, NULL);
                msgbuf[cc] = '\0';
                (void)time(&lastmsgtime);
                mailfor(msgbuf);
                sigemptyset(&sigset);
                sigprocmask(SIG_SETMASK, &sigset, NULL);
        }
}

void
reapchildren(int signo)
{
        int save_errno = errno;

        while (wait3(NULL, WNOHANG, NULL) > 0)
                ;
        errno = save_errno;
}

void
readutmp(int signo)
{
        wantreadutmp = 1;
}

void
doreadutmp(void)
{
        static u_int utmpsize;          /* last malloced size for utmp */
        static time_t utmpmtime;        /* last modification time for utmp */
        struct stat statbf;
        int n;

        if (time(NULL) - lastmsgtime >= MAXIDLE)
                exit(0);
        (void)fstat(uf, &statbf);
        if (statbf.st_mtime > utmpmtime) {
                utmpmtime = statbf.st_mtime;
                /* avoid int overflow */
                if (statbf.st_size > INT_MAX - 10 * sizeof(struct utmp)) {
                        syslog(LOG_ALERT, "utmp file excessively large");
                        exit(1);
                }
                if (statbf.st_size > utmpsize) {
                        u_int nutmpsize = statbf.st_size + 10 *
                            sizeof(struct utmp);
                        struct utmp *u;

                        if ((u = recallocarray(utmp, utmpsize,
                            nutmpsize, 1)) == NULL) {
                                free(utmp);
                                syslog(LOG_ERR, "%s", strerror(errno));
                                exit(1);
                        }
                        utmp = u;
                        utmpsize = nutmpsize;
                }
                n = pread(uf, utmp, statbf.st_size, 0);
                if (n == -1)
                        n = 0;
                nutmp = n / sizeof(struct utmp);
                dsyslog(LOG_DEBUG, "read %d utmp entries", nutmp);
        }
        (void)alarm(15);
}

void
mailfor(char *name)
{
        struct utmp *utp = &utmp[nutmp];
        char utname[UT_NAMESIZE+1];
        const char *errstr;
        char *cp;
        off_t offset;

        dsyslog(LOG_DEBUG, "mail for '%s'", name);
        if (!(cp = strchr(name, '@')))
                return;
        *cp++ = '\0';
        cp[strcspn(cp, " \t\n")] = '\0';
        offset = strtonum(cp, 0, LLONG_MAX, &errstr);
        if (errstr) {
                syslog(LOG_ERR, "'%s' is %s", cp + 1, errstr);
                return;
        }
        while (--utp >= utmp) {
                memcpy(utname, utp->ut_name, UT_NAMESIZE);
                utname[UT_NAMESIZE] = '\0';
                dsyslog(LOG_DEBUG, "check %s against %s", name, utname);
                if (!strncmp(utname, name, UT_NAMESIZE))
                        notify(utp, offset);
        }
}

static char *cr;

void
notify(struct utmp *utp, off_t offset)
{
        int fd;
        FILE *tp;
        struct stat stb;
        struct termios ttybuf;
        char tty[PATH_MAX], name[UT_NAMESIZE + 1];

        (void)snprintf(tty, sizeof(tty), "%s%.*s",
            _PATH_DEV, (int)sizeof(utp->ut_line), utp->ut_line);
        if (strchr(tty + sizeof(_PATH_DEV) - 1, '/')) {
                /* A slash is an attempt to break security... */
                syslog(LOG_AUTH | LOG_NOTICE, "'/' in \"%s\"", tty);
                return;
        }
        if (stat(tty, &stb) || !(stb.st_mode & S_IEXEC)) {
                dsyslog(LOG_DEBUG, "%.*s: wrong mode on %s",
                    (int)sizeof(utp->ut_name), utp->ut_name, tty);
                return;
        }
        dsyslog(LOG_DEBUG, "notify %.*s on %s", (int)sizeof(utp->ut_name),
            utp->ut_name, tty);
        if (fork())
                return;
        (void)signal(SIGALRM, SIG_DFL);
        (void)alarm(30);
        fd = open(tty, O_WRONLY);
        if (fd == -1 || (tp = fdopen(fd, "w")) == NULL) {
                dsyslog(LOG_ERR, "%s: %s", tty, strerror(errno));
                _exit(1);
        }
        (void)tcgetattr(fileno(tp), &ttybuf);
        cr = (ttybuf.c_oflag & ONLCR) && (ttybuf.c_oflag & OPOST) ?
            "\n" : "\n\r";
        memcpy(name, utp->ut_name, UT_NAMESIZE);
        name[UT_NAMESIZE] = '\0';
        (void)fprintf(tp, "%s\007New mail for %s@%.*s\007 has arrived:%s----%s",
            cr, name, (int)sizeof(hostname), hostname, cr, cr);
        jkfprintf(tp, name, offset);
        (void)fclose(tp);
        _exit(0);
}

void
jkfprintf(FILE *tp, char name[], off_t offset)
{
        char *cp, ch;
        char visout[5], *s2;
        FILE *fi;
        int linecnt, charcnt, inheader;
        char line[BUFSIZ];

        if ((fi = fopen(name, "r")) == NULL)
                return;

        (void)fseeko(fi, offset, SEEK_SET);
        /*
         * Print the first 7 lines or 560 characters of the new mail
         * (whichever comes first).  Skip header crap other than
         * From, Subject, To, and Date.
         */
        linecnt = 7;
        charcnt = 560;
        inheader = 1;
        while (fgets(line, sizeof(line), fi) != NULL) {
                if (inheader) {
                        if (line[0] == '\n') {
                                inheader = 0;
                                continue;
                        }
                        if (line[0] == ' ' || line[0] == '\t' ||
                            (strncmp(line, "From:", 5) &&
                            strncmp(line, "Subject:", 8)))
                                continue;
                }
                if (linecnt <= 0 || charcnt <= 0) {
                        (void)fprintf(tp, "...more...%s", cr);
                        (void)fclose(fi);
                        return;
                }
                /* strip weird stuff so can't trojan horse stupid terminals */
                for (cp = line; (ch = *cp) && ch != '\n'; ++cp, --charcnt) {
                        ch = toascii(ch);
                        vis(visout, ch, VIS_SAFE|VIS_NOSLASH, cp[1]);
                        for (s2 = visout; *s2; s2++)
                                (void)fputc(*s2, tp);
                }
                (void)fputs(cr, tp);
                --linecnt;
        }
        (void)fprintf(tp, "----%s\n", cr);
        (void)fclose(fi);
}