rlm_eap_pwd.c

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/*
 * Copyright (c) Dan Harkins, 2012
 *
 *  Copyright holder grants permission for redistribution and use in source
 *  and binary forms, with or without modification, provided that the
 *  following conditions are met:
 *     1. Redistribution of source code must retain the above copyright
 *      notice, this list of conditions, and the following disclaimer
 *      in all source files.
 *     2. Redistribution in binary form must retain the above copyright
 *      notice, this list of conditions, and the following disclaimer
 *      in the documentation and/or other materials provided with the
 *      distribution.
 *
 *  "DISCLAIMER OF LIABILITY
 *
 *  THIS SOFTWARE IS PROVIDED BY DAN HARKINS ``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 INDUSTRIAL LOUNGE 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."
 *
 * This license and distribution terms cannot be changed. In other words,
 * this code cannot simply be copied and put under a different distribution
 * license (including the GNU public license).
 */

RCSID("$Id: 9740e025e6fdc50972e5ce7ba8efbe8b96574f6c $")
USES_APPLE_DEPRECATED_API       /* OpenSSL API has been deprecated by Apple */

#include "rlm_eap_pwd.h"

#include "eap_pwd.h"

#define MPPE_KEY_LEN    32
#define MSK_EMSK_LEN    (2*MPPE_KEY_LEN)

static CONF_PARSER pwd_module_config[] = {
        { FR_CONF_OFFSET("group", PW_TYPE_INTEGER, eap_pwd_t, group), .dflt = "19" },
        { FR_CONF_OFFSET("fragment_size", PW_TYPE_INTEGER, eap_pwd_t, fragment_size), .dflt = "1020" },
        { FR_CONF_OFFSET("server_id", PW_TYPE_STRING, eap_pwd_t, server_id) },
        { FR_CONF_OFFSET("virtual_server", PW_TYPE_STRING, eap_pwd_t, virtual_server) },
        CONF_PARSER_TERMINATOR
};

static int mod_detach (void *arg)
{
        eap_pwd_t *inst;

        inst = (eap_pwd_t *) arg;

        if (inst->bnctx) BN_CTX_free(inst->bnctx);

        return 0;
}

static int mod_instantiate (CONF_SECTION *cs, void **instance)
{
        eap_pwd_t *inst;

        *instance = inst = talloc_zero(cs, eap_pwd_t);
        if (!inst) return -1;

        if (cf_section_parse(cs, inst, pwd_module_config) < 0) return -1;

        if (inst->fragment_size < 100) {
                cf_log_err_cs(cs, "Fragment size is too small");
                return -1;
        }

        if ((inst->bnctx = BN_CTX_new()) == NULL) {
                cf_log_err_cs(cs, "Failed to get BN context");
                return -1;
        }

        return 0;
}

static int _free_pwd_session (pwd_session_t *session)
{
        BN_clear_free(session->private_value);
        BN_clear_free(session->peer_scalar);
        BN_clear_free(session->my_scalar);
        BN_clear_free(session->k);
        EC_POINT_clear_free(session->my_element);
        EC_POINT_clear_free(session->peer_element);
        EC_GROUP_free(session->group);
        EC_POINT_clear_free(session->pwe);
        BN_clear_free(session->order);
        BN_clear_free(session->prime);

        return 0;
}

static int send_pwd_request (pwd_session_t *session, eap_round_t *eap_round)
{
        size_t len;
        uint16_t totlen;
        pwd_hdr *hdr;

        len = (session->out_len - session->out_pos) + sizeof(pwd_hdr);
        rad_assert(len > 0);
        eap_round->request->code = PW_EAP_REQUEST;
        eap_round->request->type.num = PW_EAP_PWD;
        eap_round->request->type.length = (len > session->mtu) ? session->mtu : len;
        eap_round->request->type.data = talloc_zero_array(eap_round->request, uint8_t, eap_round->request->type.length);
        hdr = (pwd_hdr *)eap_round->request->type.data;

        switch (session->state) {
        case PWD_STATE_ID_REQ:
                EAP_PWD_SET_EXCHANGE(hdr, EAP_PWD_EXCH_ID);
                break;

        case PWD_STATE_COMMIT:
                EAP_PWD_SET_EXCHANGE(hdr, EAP_PWD_EXCH_COMMIT);
                break;

        case PWD_STATE_CONFIRM:
                EAP_PWD_SET_EXCHANGE(hdr, EAP_PWD_EXCH_CONFIRM);
                break;

        default:
                ERROR("rlm_eap_pwd: PWD state is invalid.  Can't send request");
                return 0;
        }

        /*
         * are we fragmenting?
         */
        if (((session->out_len - session->out_pos) + sizeof(pwd_hdr)) > session->mtu) {
                EAP_PWD_SET_MORE_BIT(hdr);
                if (session->out_pos == 0) {

                        /*
                         * the first fragment, add the total length
                         */
                        EAP_PWD_SET_LENGTH_BIT(hdr);
                        totlen = ntohs(session->out_len);
                        memcpy(hdr->data, (char *)&totlen, sizeof(totlen));
                        memcpy(hdr->data + sizeof(uint16_t),
                               session->out,
                               session->mtu - sizeof(pwd_hdr) - sizeof(uint16_t));
                        session->out_pos += (session->mtu - sizeof(pwd_hdr) - sizeof(uint16_t));
                } else {
                        /*
                         * an intermediate fragment
                         */
                        memcpy(hdr->data, session->out + session->out_pos, (session->mtu - sizeof(pwd_hdr)));
                        session->out_pos += (session->mtu - sizeof(pwd_hdr));
                }
        } else {
                /*
                 * either it's not a fragment or it's the last fragment.
                 * The out buffer isn't needed anymore though so get rid of it.
                 */
                memcpy(hdr->data, session->out + session->out_pos,
                (session->out_len - session->out_pos));
                talloc_free(session->out);
                session->out = NULL;
                session->out_pos = session->out_len = 0;
        }
        return 1;
}

static int CC_HINT(nonnull) mod_process(void *instance, eap_session_t *eap_session);

static int mod_session_init (void *instance, eap_session_t *eap_session)
{
        pwd_session_t *session;
        eap_pwd_t *inst = (eap_pwd_t *)instance;
        VALUE_PAIR *vp;
        pwd_id_packet_t *packet;

        if (!inst || !eap_session) {
                ERROR("rlm_eap_pwd: Initiate, NULL data provided");
                return 0;
        }

        /*
         * make sure the server's been configured properly
         */
        if (!inst->server_id) {
                ERROR("rlm_eap_pwd: Server ID is not configured");
                return 0;
        }
        switch (inst->group) {
        case 19:
        case 20:
        case 21:
        case 25:
        case 26:
                break;

        default:
        ERROR("rlm_eap_pwd: Group is not supported");
                return 0;
        }

        if ((session = talloc_zero(eap_session, pwd_session_t)) == NULL) return 0;
        talloc_set_destructor(session, _free_pwd_session);
        /*
         * set things up so they can be free'd reliably
         */
        session->group_num = inst->group;
        session->private_value = NULL;
        session->peer_scalar = NULL;
        session->my_scalar = NULL;
        session->k = NULL;
        session->my_element = NULL;
        session->peer_element = NULL;
        session->group = NULL;
        session->pwe = NULL;
        session->order = NULL;
        session->prime = NULL;

        /*
         *      The admin can dynamically change the MTU.
         */
        session->mtu = inst->fragment_size;
        vp = fr_pair_find_by_num(eap_session->request->packet->vps, 0, PW_FRAMED_MTU, TAG_ANY);

        /*
         *      session->mtu is *our* MTU.  We need to subtract off the EAP
         *      overhead.
         *
         *      9 = 4 (EAPOL header) + 4 (EAP header) + 1 (EAP type)
         *
         *      The fragmentation code deals with the included length
         *      so we don't need to subtract that here.
         */
        if (vp && (vp->vp_integer > 100) && (vp->vp_integer < session->mtu)) {
                session->mtu = vp->vp_integer - 9;
        }

        session->state = PWD_STATE_ID_REQ;
        session->in = NULL;
        session->out_pos = 0;
        eap_session->opaque = session;

        /*
         * construct an EAP-pwd-ID/Request
         */
        session->out_len = sizeof(pwd_id_packet_t) + strlen(inst->server_id);
        if ((session->out = talloc_zero_array(session, uint8_t, session->out_len)) == NULL) return 0;

        packet = (pwd_id_packet_t *)session->out;
        packet->group_num = htons(session->group_num);
        packet->random_function = EAP_PWD_DEF_RAND_FUN;
        packet->prf = EAP_PWD_DEF_PRF;
        session->token = fr_rand();
        memcpy(packet->token, (char *)&session->token, 4);
        packet->prep = EAP_PWD_PREP_NONE;
        memcpy(packet->identity, inst->server_id, session->out_len - sizeof(pwd_id_packet_t) );

        if (!send_pwd_request(session, eap_session->this_round)) return 0;

        eap_session->process = mod_process;

        return 1;
}

static int mod_process(void *arg, eap_session_t *eap_session)
{
        pwd_session_t *session;
        pwd_hdr *hdr;
        pwd_id_packet_t *packet;
        eap_packet_t *response;
        REQUEST *request, *fake;
        VALUE_PAIR *pw, *vp;
        eap_round_t *eap_round;
        size_t in_len;
        int ret = 0;
        eap_pwd_t *inst = (eap_pwd_t *)arg;
        uint16_t offset;
        uint8_t exch, *in, *ptr, msk[MSK_EMSK_LEN], emsk[MSK_EMSK_LEN];
        uint8_t peer_confirm[SHA256_DIGEST_LENGTH];
        BIGNUM *x = NULL, *y = NULL;

        if (((eap_round = eap_session->this_round) == NULL) || !inst) return 0;

        session = (pwd_session_t *)eap_session->opaque;
        request = eap_session->request;
        response = eap_session->this_round->response;
        hdr = (pwd_hdr *)response->type.data;

        /*
         *      The header must be at least one byte.
         */
        if (!hdr || (response->type.length < sizeof(pwd_hdr))) {
                RDEBUG("Packet with insufficient data");
                return 0;
        }

        in = hdr->data;
        in_len = response->type.length - sizeof(pwd_hdr);

        /*
         * see if we're fragmenting, if so continue until we're done
         */
        if (session->out_pos) {
                if (in_len) RDEBUG2("pwd got something more than an ACK for a fragment");

                return send_pwd_request(session, eap_round);
        }

        /*
         * the first fragment will have a total length, make a
         * buffer to hold all the fragments
         */
        if (EAP_PWD_GET_LENGTH_BIT(hdr)) {
                if (session->in) {
                        RDEBUG2("pwd already alloced buffer for fragments");
                        return 0;
                }

                if (in_len < 2) {
                        RDEBUG("Invalid packet: length bit set, but no length field");
                        return 0;
                }

                session->in_len = ntohs(in[0] * 256 | in[1]);
                if ((session->in = talloc_zero_array(session, uint8_t, session->in_len)) == NULL) {
                        RDEBUG2("pwd cannot allocate %zd buffer to hold fragments", session->in_len);
                        return 0;
                }

                memset(session->in, 0, session->in_len);
                session->in_pos = 0;
                in += sizeof(uint16_t);
                in_len -= sizeof(uint16_t);
        }

        /*
         * all fragments, including the 1st will have the M(ore) bit set,
         * buffer those fragments!
         */
        if (EAP_PWD_GET_MORE_BIT(hdr)) {
                rad_assert(session->in != NULL);

                if ((session->in_pos + in_len) > session->in_len) {
                        RDEBUG2("Fragment overflows packet.");
                        return 0;
                }

                memcpy(session->in + session->in_pos, in, in_len);
                session->in_pos += in_len;

                /*
                 * send back an ACK for this fragment
                 */
                exch = EAP_PWD_GET_EXCHANGE(hdr);
                eap_round->request->code = PW_EAP_REQUEST;
                eap_round->request->type.num = PW_EAP_PWD;
                eap_round->request->type.length = sizeof(pwd_hdr);

                if ((eap_round->request->type.data = talloc_array(eap_round->request, uint8_t, sizeof(pwd_hdr))) == NULL) {
                        return 0;
                }
                hdr = (pwd_hdr *)eap_round->request->type.data;
                EAP_PWD_SET_EXCHANGE(hdr, exch);
                return 1;
        }


        if (session->in) {
                /*
                 * the last fragment...
                 */
                if ((session->in_pos + in_len) > session->in_len) {
                        RDEBUG2("pwd will not overflow a fragment buffer. Nope, not prudent");
                        return 0;
                }
                memcpy(session->in + session->in_pos, in, in_len);
                in = session->in;
                in_len = session->in_len;
        }

        switch (session->state) {
        case PWD_STATE_ID_REQ:
                if (EAP_PWD_GET_EXCHANGE(hdr) != EAP_PWD_EXCH_ID) {
                        RDEBUG2("pwd exchange is incorrect: not ID");
                        return 0;
                }

                packet = (pwd_id_packet_t *) in;
                if (in_len < sizeof(packet)) {
                        RDEBUG("Packet is too small (%zd < %zd).", in_len, sizeof(packet));
                        return 0;
                }

                if ((packet->prf != EAP_PWD_DEF_PRF) ||
                    (packet->random_function != EAP_PWD_DEF_RAND_FUN) ||
                    (packet->prep != EAP_PWD_PREP_NONE) ||
                    (CRYPTO_memcmp(packet->token, &session->token, 4)) ||
                    (packet->group_num != ntohs(session->group_num))) {
                        RDEBUG2("pwd id response is invalid");
                        return 0;
                }
                /*
                 * we've agreed on the ciphersuite, record it...
                 */
                ptr = (uint8_t *)&session->ciphersuite;
                memcpy(ptr, (char *)&packet->group_num, sizeof(uint16_t));
                ptr += sizeof(uint16_t);
                *ptr = EAP_PWD_DEF_RAND_FUN;
                ptr += sizeof(uint8_t);
                *ptr = EAP_PWD_DEF_PRF;

                session->peer_id_len = in_len - sizeof(pwd_id_packet_t);
                if (session->peer_id_len >= sizeof(session->peer_id)) {
                        RDEBUG2("pwd id response is malformed");
                        return 0;
                }

                memcpy(session->peer_id, packet->identity, session->peer_id_len);
                session->peer_id[session->peer_id_len] = '\0';

                /*
                 * make fake request to get the password for the usable ID
                 */
                if ((fake = request_alloc_fake(eap_session->request)) == NULL) {
                        RDEBUG("pwd unable to create fake request!");
                        return 0;
                }
                fake->username = fr_pair_afrom_num(fake, 0, PW_USER_NAME);
                if (!fake->username) {
                        RDEBUG("Failed creating pair for peer id");
                        talloc_free(fake);
                        return 0;
                }
                fr_pair_value_bstrncpy(fake->username, session->peer_id, session->peer_id_len);
                fr_pair_add(&fake->packet->vps, fake->username);

                if ((vp = fr_pair_find_by_num(request->config, 0, PW_VIRTUAL_SERVER, TAG_ANY)) != NULL) {
                        fake->server = vp->vp_strvalue;
                } else if (inst->virtual_server) {
                        fake->server = inst->virtual_server;
                } /* else fake->server == request->server */

                RDEBUG("Sending tunneled request");
                rdebug_pair_list(L_DBG_LVL_1, request, fake->packet->vps, NULL);

                if (fake->server) {
                        RDEBUG("server %s {", fake->server);
                } else {
                        RDEBUG("server {");
                }

                /*
                 *      Call authorization recursively, which will
                 *      get the password.
                 */
                RINDENT();
                process_authorize(0, fake);
                REXDENT();

                /*
                 *      Note that we don't do *anything* with the reply
                 *      attributes.
                 */
                if (fake->server) {
                        RDEBUG("} # server %s", fake->server);
                } else {
                        RDEBUG("}");
                }

                RDEBUG("Got tunneled reply code %d", fake->reply->code);
                rdebug_pair_list(L_DBG_LVL_1, request, fake->reply->vps, NULL);

                if ((pw = fr_pair_find_by_num(fake->config, 0, PW_CLEARTEXT_PASSWORD, TAG_ANY)) == NULL) {
                        DEBUG2("failed to find password for %s to do pwd authentication", session->peer_id);
                        talloc_free(fake);
                        return 0;
                }

                if (compute_password_element(session, session->group_num,
                                             pw->data.strvalue, strlen(pw->data.strvalue),
                                             inst->server_id, strlen(inst->server_id),
                                             session->peer_id, strlen(session->peer_id),
                                             &session->token)) {
                        DEBUG2("failed to obtain password element");
                        talloc_free(fake);
                        return 0;
                }
                TALLOC_FREE(fake);

                /*
                 * compute our scalar and element
                 */
                if (compute_scalar_element(session, inst->bnctx)) {
                        DEBUG2("failed to compute server's scalar and element");
                        return 0;
                }

                if (((x = BN_new()) == NULL) || ((y = BN_new()) == NULL)) {
                        DEBUG2("server point allocation failed");
                        return 0;
                }

                /*
                 * element is a point, get both coordinates: x and y
                 */
                if (!EC_POINT_get_affine_coordinates_GFp(session->group, session->my_element, x, y, inst->bnctx)) {
                        DEBUG2("server point assignment failed");
                        BN_clear_free(x);
                        BN_clear_free(y);
                        return 0;
                }

                /*
                 * construct request
                 */
                session->out_len = BN_num_bytes(session->order) + (2 * BN_num_bytes(session->prime));
                if ((session->out = talloc_array(session, uint8_t, session->out_len)) == NULL) {
                        return 0;
                }
                memset(session->out, 0, session->out_len);

                ptr = session->out;
                offset = BN_num_bytes(session->prime) - BN_num_bytes(x);
                BN_bn2bin(x, ptr + offset);

                ptr += BN_num_bytes(session->prime);
                offset = BN_num_bytes(session->prime) - BN_num_bytes(y);
                BN_bn2bin(y, ptr + offset);

                ptr += BN_num_bytes(session->prime);
                offset = BN_num_bytes(session->order) - BN_num_bytes(session->my_scalar);
                BN_bn2bin(session->my_scalar, ptr + offset);

                session->state = PWD_STATE_COMMIT;
                ret = send_pwd_request(session, eap_round);
                break;

        case PWD_STATE_COMMIT:
                if (EAP_PWD_GET_EXCHANGE(hdr) != EAP_PWD_EXCH_COMMIT) {
                        RDEBUG2("pwd exchange is incorrect: not commit!");
                        return 0;
                }

                /*
                 * process the peer's commit and generate the shared key, k
                 */
                if (process_peer_commit(session, in, in_len, inst->bnctx)) {
                        RDEBUG2("failed to process peer's commit");
                        return 0;
                }

                /*
                 * compute our confirm blob
                 */
                if (compute_server_confirm(session, session->my_confirm, inst->bnctx)) {
                        ERROR("rlm_eap_pwd: failed to compute confirm!");
                        return 0;
                }

                /*
                 * construct a response...which is just our confirm blob
                 */
                session->out_len = SHA256_DIGEST_LENGTH;
                if ((session->out = talloc_array(session, uint8_t, session->out_len)) == NULL) return 0;

                memset(session->out, 0, session->out_len);
                memcpy(session->out, session->my_confirm, SHA256_DIGEST_LENGTH);

                session->state = PWD_STATE_CONFIRM;
                ret = send_pwd_request(session, eap_round);
                break;

        case PWD_STATE_CONFIRM:
                if (in_len < SHA256_DIGEST_LENGTH) {
                        RDEBUG("Peer confirm is too short (%zd < %d)", in_len, SHA256_DIGEST_LENGTH);
                        return 0;
                }

                if (EAP_PWD_GET_EXCHANGE(hdr) != EAP_PWD_EXCH_CONFIRM) {
                        RDEBUG2("pwd exchange is incorrect: not commit!");
                        return 0;
                }
                if (compute_peer_confirm(session, peer_confirm, inst->bnctx)) {
                        RDEBUG2("pwd exchange cannot compute peer's confirm");
                        return 0;
                }
                if (CRYPTO_memcmp(peer_confirm, in, SHA256_DIGEST_LENGTH)) {
                        RDEBUG2("pwd exchange fails: peer confirm is incorrect!");
                        return 0;
                }
                if (compute_keys(session, peer_confirm, msk, emsk)) {
                        RDEBUG2("pwd exchange cannot generate (E)MSK!");
                        return 0;
                }
                eap_round->request->code = PW_EAP_SUCCESS;
                /*
                 * return the MSK (in halves)
                 */
                eap_add_reply(eap_session->request, "MS-MPPE-Recv-Key", msk, MPPE_KEY_LEN);
                eap_add_reply(eap_session->request, "MS-MPPE-Send-Key", msk + MPPE_KEY_LEN, MPPE_KEY_LEN);

                ret = 1;
                break;

        default:
                RDEBUG2("unknown PWD state");
                return 0;
        }


        /*
         * we processed the buffered fragments, get rid of them
         */
        if (session->in) {
                talloc_free(session->in);
                session->in = NULL;
        }

        return ret;
}

extern rlm_eap_module_t rlm_eap_pwd;
rlm_eap_module_t rlm_eap_pwd = {
        .name           = "eap_pwd",
        .instantiate    = mod_instantiate,      /* Create new submodule instance */
        .session_init   = mod_session_init,     /* Create the initial request */
        .process        = mod_process,          /* Process next round of EAP method */
        .detach         = mod_detach            /* Destroy the submodule instance */
};