/*      $NetBSD: rexecd.c,v 1.26 2008/07/20 01:09:07 lukem Exp $        */

/*
 * Copyright (c) 1983, 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/cdefs.h>
#ifndef lint
__COPYRIGHT("@(#) Copyright (c) 1983, 1993\
 The Regents of the University of California.  All rights reserved.");
#if 0
static char sccsid[] = "from: @(#)rexecd.c      8.1 (Berkeley) 6/4/93";
#else
__RCSID("$NetBSD: rexecd.c,v 1.26 2008/07/20 01:09:07 lukem Exp $");
#endif
#endif /* not lint */

#include <sys/ioctl.h>
#include <sys/param.h>
#include <sys/socket.h>
#include <sys/syslog.h>
#include <sys/time.h>

#include <netinet/in.h>

#include <err.h>
#include <errno.h>
#include <netdb.h>
#include <paths.h>
#include <poll.h>
#include <pwd.h>
#include <signal.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#ifdef USE_PAM
#include <security/pam_appl.h>
#include <security/openpam.h>
#endif

int main(int, char *[]);
static void rexecd_errx(int, const char *, ...)
     __attribute__((__noreturn__, __format__(__printf__, 2, 3)));
static void doit(struct sockaddr *) __dead;
static void getstr(char *, int, const char *);
static void usage(void) __dead;

#ifdef USE_PAM
static pam_handle_t *pamh;
static struct pam_conv pamc = {
        openpam_nullconv,
        NULL
};
static int pam_flags = PAM_SILENT|PAM_DISALLOW_NULL_AUTHTOK;
static int pam_err;
#define pam_ok(err) ((pam_err = (err)) == PAM_SUCCESS)
#endif

extern char     **environ;
static int      dolog;
#ifndef USE_PAM
static char     username[32 + 1] = "USER=";
static char     logname[32 + 3 + 1] = "LOGNAME=";
static char     homedir[PATH_MAX + 1] = "HOME=";
static char     shell[PATH_MAX + 1] = "SHELL=";
static char     path[sizeof(_PATH_DEFPATH) + sizeof("PATH=")] = "PATH=";
static char     *envinit[] = { homedir, shell, path, username, logname, 0 };
#endif

/*
 * remote execute server:
 *      username\0
 *      password\0
 *      command\0
 *      data
 */
int
main(int argc, char *argv[])
{
        struct sockaddr_storage from;
        socklen_t fromlen;
        int ch;

        while ((ch = getopt(argc, argv, "l")) != -1)
                switch (ch) {
                case 'l':
                        dolog = 1;
                        openlog("rexecd", LOG_PID, LOG_DAEMON);
                        break;
                default:
                        usage();
                }

        fromlen = sizeof(from);
        if (getpeername(STDIN_FILENO, (struct sockaddr *)&from, &fromlen) < 0)
                err(EXIT_FAILURE, "getpeername");

        if (((struct sockaddr *)&from)->sa_family == AF_INET6 &&
            IN6_IS_ADDR_V4MAPPED(&((struct sockaddr_in6 *)&from)->sin6_addr)) {
                char hbuf[NI_MAXHOST];
                if (getnameinfo((struct sockaddr *)&from, fromlen, hbuf,
                    sizeof(hbuf), NULL, 0, NI_NUMERICHOST) != 0) {
                        (void)strlcpy(hbuf, "invalid", sizeof(hbuf));
                }
                if (dolog)
                        syslog(LOG_ERR,
                            "malformed \"from\" address (v4 mapped, %s)",
                            hbuf);
                return EXIT_FAILURE;
        }

        doit((struct sockaddr *)&from);
}

void
doit(struct sockaddr *fromp)
{
        struct pollfd fds[2];
        char cmdbuf[NCARGS + 1];
        const char *cp;
        char user[16], pass[16];
        char buf[BUFSIZ], sig;
        struct passwd *pwd, pwres;
        int s = -1; /* XXX gcc */
        int pv[2], pid, cc;
        int one = 1;
        in_port_t port;
        char hostname[2 * MAXHOSTNAMELEN + 1];
        char pbuf[NI_MAXSERV];
        const int niflags = NI_NUMERICHOST | NI_NUMERICSERV;
#ifndef USE_PAM
        char *namep;
#endif
        char pwbuf[1024];

        (void)signal(SIGINT, SIG_DFL);
        (void)signal(SIGQUIT, SIG_DFL);
        (void)signal(SIGTERM, SIG_DFL);
        (void)dup2(STDIN_FILENO, STDOUT_FILENO);
        (void)dup2(STDIN_FILENO, STDERR_FILENO);

        if (getnameinfo(fromp, fromp->sa_len, hostname, sizeof(hostname),
            pbuf, sizeof(pbuf), niflags) != 0) {
                if (dolog)
                        syslog(LOG_ERR, "malformed \"from\" address (af %d)",
                               fromp->sa_family);
                exit(EXIT_FAILURE);
        }

        (void)alarm(60);
        port = 0;
        for (;;) {
                char c;
                if (read(STDIN_FILENO, &c, 1) != 1) {
                        if (dolog)
                                syslog(LOG_ERR, "initial read failed");
                        exit(EXIT_FAILURE);
                }
                if (c == 0)
                        break;
                port = port * 10 + c - '0';
        }
        if (port != 0) {
                s = socket(fromp->sa_family, SOCK_STREAM, 0);
                if (s < 0) {
                        if (dolog)
                                syslog(LOG_ERR, "socket: %m");
                        exit(EXIT_FAILURE);
                }
                (void)alarm(60);
                switch (fromp->sa_family) {
                case AF_INET:
                        ((struct sockaddr_in *)fromp)->sin_port = htons(port);
                        break;
                case AF_INET6:
                        ((struct sockaddr_in6 *)fromp)->sin6_port = htons(port);
                        break;
                default:
                        syslog(LOG_ERR, "unsupported address family");
                        exit(EXIT_FAILURE);
                }
                if (connect(s, (struct sockaddr *)fromp, fromp->sa_len) < 0) {
                        if (dolog)
                                syslog(LOG_ERR, "connect: %m");
                        exit(EXIT_FAILURE);
                }
                (void)alarm(0);
        }
        (void)alarm(60);
        getstr(user, sizeof(user), "username");
        getstr(pass, sizeof(pass), "password");
        getstr(cmdbuf, sizeof(cmdbuf), "command");
        (void)alarm(0);
        if (getpwnam_r(user, &pwres, pwbuf, sizeof(pwbuf), &pwd) != 0 ||
            pwd == NULL) {
                if (dolog)
                        syslog(LOG_ERR, "no such user %s", user);
                rexecd_errx(EXIT_FAILURE, "Login incorrect.");
        }
#ifdef USE_PAM
        if (!pam_ok(pam_start("rexecd", user, &pamc, &pamh)) ||
            !pam_ok(pam_set_item(pamh, PAM_RHOST, hostname)) ||
            !pam_ok(pam_set_item(pamh, PAM_AUTHTOK, pass))) {
                if (dolog)
                        syslog(LOG_ERR, "PAM ERROR %s@%s (%s)", user,
                           hostname, pam_strerror(pamh, pam_err));
                rexecd_errx(EXIT_FAILURE, "Try again.");
        }
        if (!pam_ok(pam_authenticate(pamh, pam_flags)) ||
            !pam_ok(pam_acct_mgmt(pamh, pam_flags))) {
                if (dolog)
                        syslog(LOG_ERR, "LOGIN REFUSED for %s@%s (%s)", user,
                           hostname, pam_strerror(pamh, pam_err));
                rexecd_errx(EXIT_FAILURE, "Password incorrect.");
        }
#else
        if (*pwd->pw_passwd != '\0') {
                namep = crypt(pass, pwd->pw_passwd);
                if (strcmp(namep, pwd->pw_passwd) != 0) {
                        if (dolog)
                                syslog(LOG_ERR, "incorrect password for %s",
                                    user);
                        rexecd_errx(EXIT_FAILURE,
                                    "Password incorrect.");/* XXX: wrong! */
                }
        } else
                (void)crypt("dummy password", "PA");    /* must always crypt */
#endif
        if (chdir(pwd->pw_dir) < 0) {
                if (dolog)
                        syslog(LOG_ERR, "%s does not exist for %s", pwd->pw_dir,
                               user);
                rexecd_errx(EXIT_FAILURE, "No remote directory.");
        }

        if (dolog)
                syslog(LOG_INFO, "login from %s as %s", hostname, user);
        (void)write(STDERR_FILENO, "\0", 1);
        if (port) {
                if (pipe(pv) < 0 || (pid = fork()) == -1) {
                        if (dolog)
                                syslog(LOG_ERR,"pipe or fork failed for %s: %m",
                                    user);
                        rexecd_errx(EXIT_FAILURE, "Try again.");
                }
                if (pid) {
                        /* parent */
#ifdef USE_PAM
                        (void)pam_end(pamh, pam_err);
#endif
                        (void)close(STDIN_FILENO);
                        (void)close(STDOUT_FILENO);
                        (void)close(STDERR_FILENO);
                        (void)close(pv[1]);
                        fds[0].fd = s;
                        fds[1].fd = pv[0];
                        fds[0].events = fds[1].events = POLLIN;
                        if (ioctl(pv[1], FIONBIO, (char *)&one) < 0)
                                _exit(1);
                        /* should set s nbio! */
                        do {
                                if (poll(fds, 2, 0) < 0) {
                                        (void)close(s);
                                        (void)close(pv[0]);
                                        _exit(1);
                                }
                                if (fds[0].revents & POLLIN) {
                                        if (read(s, &sig, 1) <= 0)
                                                fds[0].events = 0;
                                        else
                                                (void)killpg(pid, sig);
                                }
                                if (fds[1].revents & POLLIN) {
                                        cc = read(pv[0], buf, sizeof (buf));
                                        if (cc <= 0) {
                                                (void)shutdown(s, SHUT_RDWR);
                                                fds[1].events = 0;
                                        } else
                                                (void)write(s, buf, cc);
                                }
                        } while ((fds[0].events | fds[1].events) & POLLIN);
                        _exit(0);
                }
                /* child */
                (void)close(s);
                (void)close(pv[0]);
                if (dup2(pv[1], STDERR_FILENO) < 0) {
                        if (dolog)
                                syslog(LOG_ERR, "dup2 failed for %s", user);
                        rexecd_errx(EXIT_FAILURE, "Try again.");
                }
        }
        if (*pwd->pw_shell == '\0')
                pwd->pw_shell = __UNCONST(_PATH_BSHELL);
        if (setsid() < 0 ||
            setlogin(pwd->pw_name) < 0 ||
            initgroups(pwd->pw_name, pwd->pw_gid) < 0 ||
#ifdef USE_PAM
            setgid((gid_t)pwd->pw_gid) < 0) {
#else
            setgid((gid_t)pwd->pw_gid) < 0 ||
            setuid((uid_t)pwd->pw_uid) < 0) {
#endif
                rexecd_errx(EXIT_FAILURE, "Try again.");
                if (dolog)
                        syslog(LOG_ERR, "could not set permissions for %s: %m",
                            user);
                exit(EXIT_FAILURE);
        }
#ifdef USE_PAM
        if (!pam_ok(pam_setcred(pamh, PAM_ESTABLISH_CRED)))
                syslog(LOG_ERR, "pam_setcred() failed: %s",
                       pam_strerror(pamh, pam_err));
        (void)pam_setenv(pamh, "HOME", pwd->pw_dir, 1);
        (void)pam_setenv(pamh, "SHELL", pwd->pw_shell, 1);
        (void)pam_setenv(pamh, "USER", pwd->pw_name, 1);
        (void)pam_setenv(pamh, "LOGNAME", pwd->pw_name, 1);
        (void)pam_setenv(pamh, "PATH", _PATH_DEFPATH, 1);
        environ = pam_getenvlist(pamh);
        (void)pam_end(pamh, pam_err);
        if (setuid((uid_t)pwd->pw_uid) < 0) {
                if (dolog)
                        syslog(LOG_ERR, "could not set uid for %s: %m",
                            user);
                rexecd_errx(EXIT_FAILURE, "Try again.");
        }
#else
        (void)strlcat(path, _PATH_DEFPATH, sizeof(path));
        environ = envinit;
        (void)strlcat(homedir, pwd->pw_dir, sizeof(homedir));
        (void)strlcat(shell, pwd->pw_shell, sizeof(shell));
        (void)strlcat(username, pwd->pw_name, sizeof(username));
        (void)strlcat(logname, pwd->pw_name, sizeof(logname));
#endif

        cp = strrchr(pwd->pw_shell, '/');
        if (cp)
                cp++;
        else
                cp = pwd->pw_shell;
        if (dolog)
                syslog(LOG_INFO, "running command for %s: %s", user, cmdbuf);
        (void)execl(pwd->pw_shell, cp, "-c", cmdbuf, NULL);
        if (dolog)
                syslog(LOG_ERR, "execl failed for %s: %m", user);
        err(EXIT_FAILURE, "%s", pwd->pw_shell);
}

void
rexecd_errx(int ex, const char *fmt, ...)
{
        char buf[BUFSIZ];
        va_list ap;
        ssize_t len;

        va_start(ap, fmt);
        buf[0] = 1;
        len = vsnprintf(buf + 1, sizeof(buf) - 1, fmt, ap) + 1;
        buf[len++] = '\n';
        (void)write(STDERR_FILENO, buf, len);
        va_end(ap);
        exit(ex);
}

void
getstr(char *buf, int cnt, const char *emsg)
{
        char c;

        do {
                if (read(STDIN_FILENO, &c, 1) != 1)
                        exit(EXIT_FAILURE);
                *buf++ = c;
                if (--cnt == 0)
                        rexecd_errx(EXIT_FAILURE, "%s too long", emsg);
        } while (c != 0);
}

static void
usage(void)
{
        (void)fprintf(stderr, "Usage: %s [-l]\n", getprogname());
        exit(EXIT_FAILURE);
}