/*      $OpenBSD: login_skey.c,v 1.30 2023/03/08 04:43:05 guenther Exp $        */

/*
 * Copyright (c) 2000, 2001, 2004 Todd C. Miller <millert@openbsd.org>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <sys/resource.h>

#include <ctype.h>
#include <errno.h>
#include <fcntl.h>
#include <paths.h>
#include <pwd.h>
#include <readpassphrase.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <syslog.h>
#include <unistd.h>
#include <limits.h>
#include <err.h>

#include <login_cap.h>
#include <bsd_auth.h>
#include <skey.h>

#define MODE_LOGIN      0
#define MODE_CHALLENGE  1
#define MODE_RESPONSE   2

void quit(int);
void send_fd(int);
void suspend(int);

volatile sig_atomic_t resumed;
struct skey skey;

int
main(int argc, char *argv[])
{
        FILE *back = NULL;
        char *user = NULL, *cp, *ep;
        char challenge[SKEY_MAX_CHALLENGE+17], response[SKEY_MAX_PW_LEN+1];
        const char *errstr;
        int ch, fd = -1, haskey = 0, mode = MODE_LOGIN;

        (void)signal(SIGINT, quit);
        (void)signal(SIGQUIT, quit);
        (void)signal(SIGALRM, quit);
        (void)signal(SIGTSTP, suspend);
        (void)setpriority(PRIO_PROCESS, 0, 0);

        if (pledge("stdio rpath wpath flock sendfd proc tty", NULL) == -1) {
                syslog(LOG_AUTH|LOG_ERR, "pledge: %m");
                exit(1);
        }

        openlog(NULL, LOG_ODELAY, LOG_AUTH);

        while ((ch = getopt(argc, argv, "ds:v:")) != -1) {
                switch (ch) {
                case 'd':
                        back = stdout;
                        break;
                case 's':       /* service */
                        if (strcmp(optarg, "login") == 0)
                                mode = MODE_LOGIN;
                        else if (strcmp(optarg, "challenge") == 0)
                                mode = MODE_CHALLENGE;
                        else if (strcmp(optarg, "response") == 0)
                                mode = MODE_RESPONSE;
                        else {
                                syslog(LOG_ERR, "%s: invalid service", optarg);
                                exit(1);
                        }
                        break;
                case 'v':
                        if (strncmp(optarg, "fd=", 3) == 0) {
                                fd = strtonum(optarg + 3, 0, INT_MAX, &errstr);
                                if (errstr != NULL) {
                                        syslog(LOG_ERR, "fd is %s: %s",
                                            errstr, optarg + 3);
                                        fd = -1;
                                }
                        }
                        /* silently ignore unsupported variables */
                        break;
                default:
                        syslog(LOG_ERR, "usage error");
                        exit(1);
                }
        }
        argc -= optind;
        argv += optind;

        switch (argc) {
        case 2: /* silently ignore class */
        case 1:
                user = *argv;
                break;
        default:
                syslog(LOG_ERR, "usage error");
                exit(1);
        }

        if (back == NULL && (back = fdopen(3, "r+")) == NULL)  {
                syslog(LOG_ERR, "reopening back channel: %m");
                exit(1);
        }

        /*
         * Note: our skeychallenge2() will always fill in the challenge,
         *       even if it has to create a fake one.
         */
        switch (mode) {
        case MODE_LOGIN:
                haskey = (skeychallenge2(fd, &skey, user, challenge) == 0);
                strlcat(challenge, "\nS/Key Password:", sizeof(challenge));

                /* time out getting passphrase after 2 minutes to avoid a DoS */
                if (haskey)
                        alarm(120);
                resumed = 0;
                if (!readpassphrase(challenge, response, sizeof(response), 0))
                        exit(1);
                if (response[0] == '\0')
                        readpassphrase("S/Key Password [echo on]: ",
                            response, sizeof(response), RPP_ECHO_ON);
                alarm(0);
                if (resumed) {
                        /*
                         * We were suspended by the user.  Our lock is
                         * no longer valid so we must regain it so
                         * an attacker cannot do a partial guess of
                         * an S/Key response already in progress.
                         */
                        haskey = (skeylookup(&skey, user) == 0);
                }
                break;

        case MODE_CHALLENGE:
                haskey = (skeychallenge2(fd, &skey, user, challenge) == 0);
                strlcat(challenge, "\nS/Key Password:", sizeof(challenge));
                cp = auth_mkvalue(challenge);
                if (cp == NULL) {
                        (void)fprintf(back, BI_VALUE " errormsg %s\n",
                            "unable to allocate memory");
                        (void)fprintf(back, BI_REJECT "\n");
                        exit(1);
                }
                fprintf(back, BI_VALUE " challenge %s\n", cp);
                fprintf(back, BI_CHALLENGE "\n");
                if (haskey) {
                        fprintf(back, BI_FDPASS "\n");
                        fflush(back);
                        send_fd(fileno(back));
                }
                exit(0);

        case MODE_RESPONSE:
                /* read challenge */
                mode = -1;
                cp = challenge;
                ep = challenge + sizeof(challenge);
                while (cp < ep && read(fileno(back), cp, 1) == 1) {
                        if (*cp++ == '\0') {
                                mode = MODE_CHALLENGE;
                                break;
                        }
                }
                if (mode != MODE_CHALLENGE) {
                        syslog(LOG_ERR,
                            "protocol error: bad/missing challenge");
                        exit(1);
                }

                /* read response */
                cp = response;
                ep = response + sizeof(response);
                while (cp < ep && read(fileno(back), cp, 1) == 1) {
                        if (*cp++ == '\0') {
                                mode = MODE_RESPONSE;
                                break;
                        }
                }
                if (mode != MODE_RESPONSE) {
                        syslog(LOG_ERR,
                            "protocol error: bad/missing response");
                        exit(1);
                }

                /*
                 * Since the entry is locked we do not need to compare
                 * the passed in challenge to the S/Key database but
                 * maybe we should anyway?
                 */
                haskey = (skeychallenge2(fd, &skey, user, challenge) == 0);
                break;
        }

        /*
         * Ignore keyboard interrupt/suspend during database update.
         */
        signal(SIGINT, SIG_IGN);
        signal(SIGQUIT, SIG_IGN);
        signal(SIGTSTP, SIG_IGN);

        if (haskey && skeyverify(&skey, response) == 0) {
                if (mode == MODE_LOGIN) {
                        if (skey.n <= 1)
                                printf("Warning! You MUST change your "
                                    "S/Key password now!\n");
                        else if (skey.n < 5)
                                printf("Warning! Change S/Key password soon\n");
                }
                fprintf(back, BI_AUTH "\n");
                fprintf(back, BI_SECURE "\n");
                exit(0);
        }
        fprintf(back, BI_REJECT "\n");
        exit(1);
}

void
quit(int signo)
{

        _exit(1);
}

void
suspend(int signo)
{
        sigset_t nset;
        int save_errno = errno;

        /*
         * Unlock the skey record so we don't sleep holding the lock.
         * Unblock SIGTSTP, set it to the default action and then
         * resend it so we are suspended properly.
         * When we resume, reblock SIGTSTP, reset the signal handler,
         * set a flag and restore errno.
         */
        alarm(0);
        skey_unlock(&skey);
        (void)signal(signo, SIG_DFL);
        (void)sigemptyset(&nset);
        (void)sigaddset(&nset, signo);
        (void)sigprocmask(SIG_UNBLOCK, &nset, NULL);
        (void)kill(getpid(), signo);
        (void)sigprocmask(SIG_BLOCK, &nset, NULL);
        (void)signal(signo, suspend);
        resumed = 1;
        errno = save_errno;
}

void
send_fd(int sock)
{
        struct msghdr msg;
        struct cmsghdr *cmp;
        union {
                struct cmsghdr hdr;
                char buf[CMSG_SPACE(sizeof(int))];
        } cmsgbuf;

        memset(&msg, 0, sizeof(msg));
        msg.msg_control = &cmsgbuf.buf;
        msg.msg_controllen = sizeof(cmsgbuf.buf);

        cmp = CMSG_FIRSTHDR(&msg);
        cmp->cmsg_len = CMSG_LEN(sizeof(int));
        cmp->cmsg_level = SOL_SOCKET;
        cmp->cmsg_type = SCM_RIGHTS;

        *(int *)CMSG_DATA(cmp) = fileno(skey.keyfile);

        if (sendmsg(sock, &msg, 0) == -1)
                syslog(LOG_ERR, "sendmsg: %m");
}