auth2-gss.c

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/*      $OpenBSD: auth2-gss.c,v 1.12 2005/10/13 22:24:31 stevesk Exp $  */

/*
 * Copyright (c) 2001-2003 Simon Wilkinson. 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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 "includes.h"

#ifdef GSSAPI

#include "auth.h"
#include "ssh2.h"
#include "xmalloc.h"
#include "log.h"
#include "dispatch.h"
#include "servconf.h"
#include "packet.h"
#include "monitor_wrap.h"

#include "ssh-gss.h"

extern ServerOptions options;

static void input_gssapi_token(int type, u_int32_t plen, void *ctxt);
static void input_gssapi_mic(int type, u_int32_t plen, void *ctxt);
static void input_gssapi_exchange_complete(int type, u_int32_t plen, void *ctxt);
static void input_gssapi_errtok(int, u_int32_t, void *);

/*
 * We only support those mechanisms that we know about (ie ones that we know
 * how to check local user kuserok and the like)
 */
static int
userauth_gssapi(Authctxt *authctxt)
{
        gss_OID_desc goid = {0, NULL};
        Gssctxt *ctxt = NULL;
        int mechs;
        gss_OID_set supported;
        int present;
        OM_uint32 ms;
        u_int len;
        u_char *doid = NULL;

        if (!authctxt->valid || authctxt->user == NULL)
                return (0);

        mechs = packet_get_int();
        if (mechs == 0) {
                debug("Mechanism negotiation is not supported");
                return (0);
        }

        ssh_gssapi_supported_oids(&supported);
        do {
                mechs--;

                if (doid)
                        xfree(doid);

                present = 0;
                doid = packet_get_string(&len);

                if (len > 2 && doid[0] == SSH_GSS_OIDTYPE &&
                    doid[1] == len - 2) {
                        goid.elements = doid + 2;
                        goid.length   = len - 2;
                        gss_test_oid_set_member(&ms, &goid, supported,
                            &present);
                } else {
                        logit("Badly formed OID received");
                }
        } while (mechs > 0 && !present);

        gss_release_oid_set(&ms, &supported);

        if (!present) {
                xfree(doid);
                return (0);
        }

        if (GSS_ERROR(PRIVSEP(ssh_gssapi_server_ctx(&ctxt, &goid)))) {
                xfree(doid);
                return (0);
        }

        authctxt->methoddata = (void *)ctxt;

        packet_start(SSH2_MSG_USERAUTH_GSSAPI_RESPONSE);

        /* Return the OID that we received */
        packet_put_string(doid, len);

        packet_send();
        xfree(doid);

        dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_TOKEN, &input_gssapi_token);
        dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_ERRTOK, &input_gssapi_errtok);
        authctxt->postponed = 1;

        return (0);
}

static void
input_gssapi_token(int type, u_int32_t plen, void *ctxt)
{
        Authctxt *authctxt = ctxt;
        Gssctxt *gssctxt;
        gss_buffer_desc send_tok = GSS_C_EMPTY_BUFFER;
        gss_buffer_desc recv_tok;
        OM_uint32 maj_status, min_status, flags;
        u_int len;

        if (authctxt == NULL || (authctxt->methoddata == NULL && !use_privsep))
                fatal("No authentication or GSSAPI context");

        gssctxt = authctxt->methoddata;
        recv_tok.value = packet_get_string(&len);
        recv_tok.length = len; /* u_int vs. size_t */

        packet_check_eom();

        maj_status = PRIVSEP(ssh_gssapi_accept_ctx(gssctxt, &recv_tok,
            &send_tok, &flags));

        xfree(recv_tok.value);

        if (GSS_ERROR(maj_status)) {
                if (send_tok.length != 0) {
                        packet_start(SSH2_MSG_USERAUTH_GSSAPI_ERRTOK);
                        packet_put_string(send_tok.value, send_tok.length);
                        packet_send();
                }
                authctxt->postponed = 0;
                dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
                userauth_finish(authctxt, 0, "gssapi-with-mic");
        } else {
                if (send_tok.length != 0) {
                        packet_start(SSH2_MSG_USERAUTH_GSSAPI_TOKEN);
                        packet_put_string(send_tok.value, send_tok.length);
                        packet_send();
                }
                if (maj_status == GSS_S_COMPLETE) {
                        dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
                        if (flags & GSS_C_INTEG_FLAG)
                                dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_MIC,
                                    &input_gssapi_mic);
                        else
                                dispatch_set(
                                    SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE,
                                    &input_gssapi_exchange_complete);
                }
        }

        gss_release_buffer(&min_status, &send_tok);
}

static void
input_gssapi_errtok(int type, u_int32_t plen, void *ctxt)
{
        Authctxt *authctxt = ctxt;
        Gssctxt *gssctxt;
        gss_buffer_desc send_tok = GSS_C_EMPTY_BUFFER;
        gss_buffer_desc recv_tok;
        OM_uint32 maj_status;
        u_int len;

        if (authctxt == NULL || (authctxt->methoddata == NULL && !use_privsep))
                fatal("No authentication or GSSAPI context");

        gssctxt = authctxt->methoddata;
        recv_tok.value = packet_get_string(&len);
        recv_tok.length = len;

        packet_check_eom();

        /* Push the error token into GSSAPI to see what it says */
        maj_status = PRIVSEP(ssh_gssapi_accept_ctx(gssctxt, &recv_tok,
            &send_tok, NULL));

        xfree(recv_tok.value);

        /* We can't return anything to the client, even if we wanted to */
        dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
        dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_ERRTOK, NULL);

        /* The client will have already moved on to the next auth */

        gss_release_buffer(&maj_status, &send_tok);
}

/*
 * This is called when the client thinks we've completed authentication.
 * It should only be enabled in the dispatch handler by the function above,
 * which only enables it once the GSSAPI exchange is complete.
 */

static void
input_gssapi_exchange_complete(int type, u_int32_t plen, void *ctxt)
{
        Authctxt *authctxt = ctxt;
        Gssctxt *gssctxt;
        int authenticated;

        if (authctxt == NULL || (authctxt->methoddata == NULL && !use_privsep))
                fatal("No authentication or GSSAPI context");

        gssctxt = authctxt->methoddata;

        /*
         * We don't need to check the status, because we're only enabled in
         * the dispatcher once the exchange is complete
         */

        packet_check_eom();

        authenticated = PRIVSEP(ssh_gssapi_userok(authctxt->user));

        authctxt->postponed = 0;
        dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
        dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_ERRTOK, NULL);
        dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_MIC, NULL);
        dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL);
        userauth_finish(authctxt, authenticated, "gssapi-with-mic");
}

static void
input_gssapi_mic(int type, u_int32_t plen, void *ctxt)
{
        Authctxt *authctxt = ctxt;
        Gssctxt *gssctxt;
        int authenticated = 0;
        Buffer b;
        gss_buffer_desc mic, gssbuf;
        u_int len;

        if (authctxt == NULL || (authctxt->methoddata == NULL && !use_privsep))
                fatal("No authentication or GSSAPI context");

        gssctxt = authctxt->methoddata;

        mic.value = packet_get_string(&len);
        mic.length = len;

        ssh_gssapi_buildmic(&b, authctxt->user, authctxt->service,
            "gssapi-with-mic");

        gssbuf.value = buffer_ptr(&b);
        gssbuf.length = buffer_len(&b);

        if (!GSS_ERROR(PRIVSEP(ssh_gssapi_checkmic(gssctxt, &gssbuf, &mic))))
                authenticated = PRIVSEP(ssh_gssapi_userok(authctxt->user));
        else
                logit("GSSAPI MIC check failed");

        buffer_free(&b);
        xfree(mic.value);

        authctxt->postponed = 0;
        dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
        dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_ERRTOK, NULL);
        dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_MIC, NULL);
        dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL);
        userauth_finish(authctxt, authenticated, "gssapi-with-mic");
}

Authmethod method_gssapi = {
        "gssapi-with-mic",
        userauth_gssapi,
        &options.gss_authentication
};

#endif /* GSSAPI */

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