openssh/sources/kexgssc.c

	kexgssc.c revision 5322
/*
 * Copyright (c) 2001-2009 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.
 */

/*
 * May 22, 2015
 * In version 6.8 a new packet interface has been introduced to OpenSSH,
 * while the old packet API has been provided in opacket.c.
 * At this moment we are not rewritting GSS-API key exchange code to the new
 * API, just adjusting it to still work with new struct ssh.
 * Rewritting to the new API can be considered in the future.
 */

#include "includes.h"

#ifdef GSSAPI

#include "includes.h"

#include <openssl/crypto.h>
#include <openssl/bn.h>

#include <signal.h> /* for sig_atomic_t in kex.h */
#include <string.h>

#include "xmalloc.h"
#include "buffer.h"
#include "ssh2.h"
#include "key.h"
#include "cipher.h"
#include "digest.h"
#include "kex.h"
#include "log.h"
#include "packet.h"
#include "dh.h"

#include "ssh-gss.h"

int
kexgss_client(struct ssh *ssh) {
    gss_buffer_desc send_tok = GSS_C_EMPTY_BUFFER;
    gss_buffer_desc recv_tok, gssbuf, msg_tok, *token_ptr;
    Gssctxt *ctxt;
    OM_uint32 maj_status, min_status, ret_flags;
    uint_t klen, kout, slen = 0, strlen;
    DH *dh;
    BIGNUM *dh_server_pub = NULL;
    BIGNUM *shared_secret = NULL;
    BIGNUM *p = NULL;
    BIGNUM *g = NULL;
    uchar_t *kbuf;
    uchar_t *serverhostkey = NULL;
    uchar_t *empty = "";
    char *msg;
    char *lang;
    int type = 0;
    int first = 1;
    int nbits = 0, min = DH_GRP_MIN, max = DH_GRP_MAX;
    struct kex *kex = ssh->kex;
    int r;
    uchar_t hash[SSH_DIGEST_MAX_LENGTH];
    size_t hashlen;

    /* Initialise our GSSAPI world */
    ssh_gssapi_build_ctx(&ctxt);
    if (ssh_gssapi_id_kex(ctxt, kex->name, kex->kex_type)
        == GSS_C_NO_OID)
        fatal("Couldn't identify host exchange");

    if (ssh_gssapi_import_name(ctxt, kex->gss_host))
        fatal("Couldn't import hostname");

    switch (kex->kex_type) {
    case KEX_GSS_GRP1_SHA1:
        kex->dh = dh_new_group1();
        break;
    case KEX_GSS_GRP14_SHA1:
        kex->dh = dh_new_group14();
        break;
    case KEX_GSS_GEX_SHA1:
        debug("Doing group exchange\n");
        nbits = dh_estimate(kex->we_need * 8);
        packet_start(SSH2_MSG_KEXGSS_GROUPREQ);
        packet_put_int(min);
        packet_put_int(nbits);
        packet_put_int(max);

        packet_send();

        packet_read_expect(SSH2_MSG_KEXGSS_GROUP);

        if ((p = BN_new()) == NULL)
            fatal("BN_new() failed");
        packet_get_bignum2(p);
        if ((g = BN_new()) == NULL)
            fatal("BN_new() failed");
        packet_get_bignum2(g);
        packet_check_eom();

        if (BN_num_bits(p) < min || BN_num_bits(p) > max)
            fatal("GSSGRP_GEX group out of range: %d !< %d !< %d",
                min, BN_num_bits(p), max);

        kex->dh = dh_new_group(g, p);
        break;
    default:
        fatal("%s: Unexpected KEX type %d", __func__, kex->kex_type);
    }

    /* Step 1 - e is dh->pub_key */
    dh_gen_key(kex->dh, kex->we_need * 8);

    /* This is f, we initialise it now to make life easier */
    dh_server_pub = BN_new();
    if (dh_server_pub == NULL)
        fatal("dh_server_pub == NULL");

    token_ptr = GSS_C_NO_BUFFER;

    do {
        debug("Calling gss_init_sec_context");

        maj_status = ssh_gssapi_init_ctx(ctxt,
            kex->gss_deleg_creds, token_ptr, &send_tok,
            &ret_flags);

        if (GSS_ERROR(maj_status)) {
            if (send_tok.length != 0) {
                packet_start(SSH2_MSG_KEXGSS_CONTINUE);
                packet_put_string(send_tok.value,
                    send_tok.length);
            }
            fatal("gss_init_context failed");
        }

        /* If we've got an old receive buffer get rid of it */
        if (token_ptr != GSS_C_NO_BUFFER)
            free(recv_tok.value);

        if (maj_status == GSS_S_COMPLETE) {
            /* If mutual state flag is not true, kex fails */
            if (!(ret_flags & GSS_C_MUTUAL_FLAG))
                fatal("Mutual authentication failed");

            /* If integ avail flag is not true kex fails */
            if (!(ret_flags & GSS_C_INTEG_FLAG))
                fatal("Integrity check failed");
        }

        /*
         * If we have data to send, then the last message that we
         * received cannot have been a 'complete'.
         */
        if (send_tok.length != 0) {
            if (first) {
                packet_start(SSH2_MSG_KEXGSS_INIT);
                packet_put_string(send_tok.value,
                    send_tok.length);
                packet_put_bignum2(kex->dh->pub_key);
                first = 0;
            } else {
                packet_start(SSH2_MSG_KEXGSS_CONTINUE);
                packet_put_string(send_tok.value,
                    send_tok.length);
            }
            packet_send();
            gss_release_buffer(&min_status, &send_tok);

            /* If we've sent them data, they should reply */
            do {
                type = packet_read();
                if (type == SSH2_MSG_KEXGSS_HOSTKEY) {
                    debug("Received KEXGSS_HOSTKEY");
                    if (serverhostkey)
                        fatal("Server host key received"
                            "more than once");
                    serverhostkey =
                        packet_get_string(&slen);
                }
            } while (type == SSH2_MSG_KEXGSS_HOSTKEY);

            switch (type) {
            case SSH2_MSG_KEXGSS_CONTINUE:
                debug("Received GSSAPI_CONTINUE");
                if (maj_status == GSS_S_COMPLETE)
                    fatal("GSSAPI Continue received from"
                        "server when complete");
                recv_tok.value = packet_get_string(&strlen);
                recv_tok.length = strlen;
                break;
            case SSH2_MSG_KEXGSS_COMPLETE:
                debug("Received GSSAPI_COMPLETE");
                packet_get_bignum2(dh_server_pub);
                msg_tok.value =  packet_get_string(&strlen);
                msg_tok.length = strlen;

                /* Is there a token included? */
                if (packet_get_char()) {
                    recv_tok.value=
                        packet_get_string(&strlen);
                    recv_tok.length = strlen;
                    /* If complete - protocol error */
                    if (maj_status == GSS_S_COMPLETE)
                        packet_disconnect("Protocol"
                            " error: received token"
                            " when complete");
                } else {
                    /* No token included */
                    if (maj_status != GSS_S_COMPLETE)
                        packet_disconnect("Protocol"
                            " error: did not receive"
                            " final token");
                }
                break;
            case SSH2_MSG_KEXGSS_ERROR:
                debug("Received Error");
                maj_status = packet_get_int();
                min_status = packet_get_int();
                msg = packet_get_string(NULL);
                lang = packet_get_string(NULL);
                fatal("GSSAPI Error: \n%.400s", msg);
            default:
                packet_disconnect("Protocol error: didn't"
                    " expect packet type %d", type);
            }
            token_ptr = &recv_tok;
        } else {
            /* No data, and not complete */
            if (maj_status != GSS_S_COMPLETE)
                fatal("Not complete, and no token output");
        }
    } while (maj_status & GSS_S_CONTINUE_NEEDED);

    /*
     * We _must_ have received a COMPLETE message in reply from the
     * server, which will have set dh_server_pub and msg_tok
     */

    if (type != SSH2_MSG_KEXGSS_COMPLETE)
        fatal("Didn't receive SSH2_MSG_KEXGSS_COMPLETE when expected");

    /* Check f in range [1, p-1] */
    if (!dh_pub_is_valid(kex->dh, dh_server_pub))
        packet_disconnect("bad server public DH value");

    /* compute K=f^x mod p */
    klen = DH_size(kex->dh);
    kbuf = xmalloc(klen);
    kout = DH_compute_key(kbuf, dh_server_pub, kex->dh);
    if (kout < 0)
        fatal("DH_compute_key: failed");

    shared_secret = BN_new();
    if (shared_secret == NULL)
        fatal("kexgss_client: BN_new failed");

    if (BN_bin2bn(kbuf, kout, shared_secret) == NULL)
        fatal("kexdh_client: BN_bin2bn failed");

    memset(kbuf, 0, klen);
    free(kbuf);

    hashlen = sizeof (hash);
    switch (kex->kex_type) {
    case KEX_GSS_GRP1_SHA1:
    case KEX_GSS_GRP14_SHA1:
        kex_dh_hash(kex->client_version_string,
            kex->server_version_string,
            buffer_ptr(kex->my), buffer_len(kex->my),
            buffer_ptr(kex->peer), buffer_len(kex->peer),
            (serverhostkey ? serverhostkey : empty), slen,
            kex->dh->pub_key,   /* e */
            dh_server_pub,  /* f */
            shared_secret,  /* K */
            hash, &hashlen);
        break;
    case KEX_GSS_GEX_SHA1:
        kexgex_hash(
            kex->hash_alg,
            kex->client_version_string,
            kex->server_version_string,
            buffer_ptr(kex->my), buffer_len(kex->my),
            buffer_ptr(kex->peer), buffer_len(kex->peer),
            (serverhostkey ? serverhostkey : empty), slen,
            min, nbits, max,
            kex->dh->p, kex->dh->g,
            kex->dh->pub_key,
            dh_server_pub,
            shared_secret,
            hash, &hashlen);
        break;
    default:
        fatal("%s: Unexpected KEX type %d", __func__, kex->kex_type);
    }

    gssbuf.value = hash;
    gssbuf.length = hashlen;

    /* Verify that the hash matches the MIC we just got. */
    if (GSS_ERROR(ssh_gssapi_checkmic(ctxt, &gssbuf, &msg_tok)))
        packet_disconnect("Hash's MIC didn't verify");

    free(msg_tok.value);

    DH_free(kex->dh);
    if (serverhostkey)
        free(serverhostkey);
    BN_clear_free(dh_server_pub);

    /* save session id */
    if (kex->session_id == NULL) {
        kex->session_id_len = hashlen;
        kex->session_id = xmalloc(kex->session_id_len);
        memcpy(kex->session_id, hash, kex->session_id_len);
    }

    if (gss_kex_context == NULL)
        gss_kex_context = ctxt;
    else
        ssh_gssapi_delete_ctx(&ctxt);

    if ((r = kex_derive_keys_bn(ssh, hash, hashlen, shared_secret)) == 0)
        r = kex_send_newkeys(ssh);
    return (r);
}

#endif /* GSSAPI */