rlm_yubikey.c

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/*
 *   This program is is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
 *   the Free Software Foundation; either version 2 of the License, or (at
 *   your option) any later version.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *   GNU General Public License for more details.
 *
 *   You should have received a copy of the GNU General Public License
 *   along with this program; if not, write to the Free Software
 *   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
 */
 
/**
 * $Id: 74c01429bc276dba88842e11693f03ab8f49f3f8 $
 * @file rlm_yubikey.c
 * @brief Authentication for yubikey OTP tokens.
 *
 * @author Arran Cudbard-Bell (a.cudbardb@networkradius.com)
 * @copyright 2013 The FreeRADIUS server project
 * @copyright 2013 Network RADIUS (legal@networkradius.com)
 */
RCSID("$Id: 74c01429bc276dba88842e11693f03ab8f49f3f8 $")
 
#include <freeradius-devel/radius/radius.h>
#include <freeradius-devel/unlang/xlat_func.h>
#include <freeradius-devel/server/rcode.h>
#include "rlm_yubikey.h"
 
#ifdef HAVE_YKCLIENT
static const conf_parser_t validation_config[] = {
        { FR_CONF_OFFSET("client_id", rlm_yubikey_t, client_id), .dflt = 0 },
        { FR_CONF_OFFSET_FLAGS("api_key", CONF_FLAG_SECRET, rlm_yubikey_t, api_key) },
        CONF_PARSER_TERMINATOR
};
#endif
 
static const conf_parser_t module_config[] = {
        { FR_CONF_OFFSET("id_length", rlm_yubikey_t, id_len), .dflt = "12" },
        { FR_CONF_OFFSET("split", rlm_yubikey_t, split), .dflt = "yes" },
        { FR_CONF_OFFSET("decrypt", rlm_yubikey_t, decrypt), .dflt = "no" },
        { FR_CONF_OFFSET("validate", rlm_yubikey_t, validate), .dflt = "no" },
#ifdef HAVE_YKCLIENT
        { FR_CONF_POINTER("validation", 0, CONF_FLAG_SUBSECTION, NULL), .subcs = (void const *) validation_config },
#endif
        CONF_PARSER_TERMINATOR
};
 
static fr_dict_t const *dict_freeradius;
static fr_dict_t const *dict_radius;
 
extern fr_dict_autoload_t rlm_yubikey_dict[];
fr_dict_autoload_t rlm_yubikey_dict[] = {
        { .out = &dict_freeradius, .proto = "freeradius" },
        { .out = &dict_radius, .proto = "radius" },
        DICT_AUTOLOAD_TERMINATOR
};
 
fr_dict_attr_t const *attr_auth_type;
fr_dict_attr_t const *attr_user_password;
fr_dict_attr_t const *attr_yubikey_key;
fr_dict_attr_t const *attr_yubikey_public_id;
fr_dict_attr_t const *attr_yubikey_private_id;
fr_dict_attr_t const *attr_yubikey_counter;
fr_dict_attr_t const *attr_yubikey_timestamp;
fr_dict_attr_t const *attr_yubikey_random;
fr_dict_attr_t const *attr_yubikey_otp;
 
extern fr_dict_attr_autoload_t rlm_yubikey_dict_attr[];
fr_dict_attr_autoload_t rlm_yubikey_dict_attr[] = {
        { .out = &attr_auth_type, .name = "Auth-Type", .type = FR_TYPE_UINT32, .dict = &dict_freeradius },
        { .out = &attr_user_password, .name = "User-Password", .type = FR_TYPE_STRING, .dict = &dict_radius },
        { .out = &attr_yubikey_key, .name = "Vendor-Specific.Yubico.Yubikey-Key", .type = FR_TYPE_OCTETS, .dict = &dict_radius },
        { .out = &attr_yubikey_public_id, .name = "Vendor-Specific.Yubico.Yubikey-Public-ID", .type = FR_TYPE_STRING, .dict = &dict_radius },
        { .out = &attr_yubikey_private_id, .name = "Vendor-Specific.Yubico.Yubikey-Private-ID", .type = FR_TYPE_OCTETS, .dict = &dict_radius },
        { .out = &attr_yubikey_counter, .name = "Vendor-Specific.Yubico.Yubikey-Counter", .type = FR_TYPE_UINT32, .dict = &dict_radius },
        { .out = &attr_yubikey_timestamp, .name = "Vendor-Specific.Yubico.Yubikey-Timestamp", .type = FR_TYPE_UINT32, .dict = &dict_radius },
        { .out = &attr_yubikey_random, .name = "Vendor-Specific.Yubico.Yubikey-Random", .type = FR_TYPE_UINT32, .dict = &dict_radius },
        { .out = &attr_yubikey_otp, .name = "Vendor-Specific.Yubico.Yubikey-OTP", .type = FR_TYPE_STRING, .dict = &dict_radius },
        DICT_AUTOLOAD_TERMINATOR
};
 
static char const modhextab[] = "cbdefghijklnrtuv";
static char const hextab[] = "0123456789abcdef";
 
#define is_modhex(x) (memchr(modhextab, tolower(x), 16))
 
/** Convert yubikey modhex to normal hex
 *
 * The same buffer may be passed as modhex and hex to convert the modhex in place.
 *
 * Modhex and hex must be the same size.
 *
 * @param[in] modhex data.
 * @param[in] len of input and output buffers.
 * @param[out] hex where to write the standard hexits.
 * @return
 *      - The number of bytes written to the output buffer.
 *      - -1 on failure.
 */
static ssize_t modhex2hex(char const *modhex, char *hex, size_t len)
{
        size_t i;
        char *c1, *c2;
 
        for (i = 0; i < len; i += 2) {
                if (modhex[i] == '\0') {
                        break;
                }
 
                /*
                 *      We only deal with whole bytes
                 */
                if (modhex[i + 1] == '\0')
                        return -1;
 
                if (!(c1 = memchr(modhextab, tolower((uint8_t) modhex[i]), 16)) ||
                    !(c2 = memchr(modhextab, tolower((uint8_t) modhex[i + 1]), 16)))
                        return -1;
 
                hex[i] = hextab[c1 - modhextab];
                hex[i + 1] = hextab[c2 - modhextab];
        }
 
        return i;
}
 
static xlat_arg_parser_t const modhex_to_hex_xlat_arg[] = {
        { .required = true, .concat = true, .type = FR_TYPE_STRING },
        XLAT_ARG_PARSER_TERMINATOR
};
 
/** Xlat to convert Yubikey modhex to standard hex
 *
 * Example:
@verbatim
%modhextohex('vvrbuctetdhc') == "ffc1e0d3d260"
@endverbatim
 *
 * @ingroup xlat_functions
 */
static xlat_action_t modhex_to_hex_xlat(UNUSED TALLOC_CTX *ctx, fr_dcursor_t * out,
                                        UNUSED xlat_ctx_t const *xctx, request_t *request,
                                        fr_value_box_list_t *in)
{
        ssize_t         len;
        fr_value_box_t  *arg = fr_value_box_list_pop_head(in);
        char            *p = UNCONST(char *, arg->vb_strvalue);
 
        /*
         *      mod2hex allows conversions in place
         */
        len = modhex2hex(p, p, arg->vb_length);
        if (len <= 0) {
                REDEBUG("Modhex string invalid");
                talloc_free(arg);
                return XLAT_ACTION_FAIL;
        }
 
        fr_dcursor_append(out, arg);
        return XLAT_ACTION_DONE;
}
 
static int mod_load(void)
{
        xlat_t          *xlat;
 
        if (fr_dict_autoload(rlm_yubikey_dict) < 0) {
                PERROR("%s", __FUNCTION__);
                return -1;
        }
 
        if (fr_dict_attr_autoload(rlm_yubikey_dict_attr) < 0) {
                PERROR("%s", __FUNCTION__);
                fr_dict_autofree(rlm_yubikey_dict);
                return -1;
        }
 
        if (unlikely(!(xlat = xlat_func_register(NULL, "modhextohex", modhex_to_hex_xlat, FR_TYPE_STRING)))) return -1;
        xlat_func_args_set(xlat, modhex_to_hex_xlat_arg);
        xlat_func_flags_set(xlat, XLAT_FUNC_FLAG_PURE);
 
        return 0;
}
 
static void mod_unload(void)
{
        xlat_func_unregister("modhextohex");
        fr_dict_autofree(rlm_yubikey_dict);
}
 
#ifndef HAVE_YUBIKEY
static int mod_bootstrap(module_inst_ctx_t const *mctx)
{
        rlm_yubikey_t const *inst = talloc_get_type_abort(mctx->mi->data, rlm_yubikey_t);
 
        if (inst->decrypt) {
                cf_log_err(mctx->mi->conf, "Requires libyubikey for OTP decryption");
                return -1;
        }
        return 0;
}
#endif
 
/*
 *      Do any per-module initialization that is separate to each
 *      configured instance of the module.  e.g. set up connections
 *      to external databases, read configuration files, set up
 *      dictionary entries, etc.
 *
 *      If configuration information is given in the config section
 *      that must be referenced in later calls, store a handle to it
 *      in *instance otherwise put a null pointer there.
 */
static int mod_instantiate(module_inst_ctx_t const *mctx)
{
        rlm_yubikey_t   *inst = talloc_get_type_abort(mctx->mi->data, rlm_yubikey_t);
        CONF_SECTION    *conf = mctx->mi->conf;
 
        inst->name = mctx->mi->name;
 
        inst->auth_type = fr_dict_enum_by_name(attr_auth_type, inst->name, -1);
        if (!inst->auth_type) {
                WARN("Failed to find 'authenticate %s {...}' section.  Yubikey authentication will likely not work",
                     mctx->mi->name);
        }
 
        if (inst->validate) {
#ifdef HAVE_YKCLIENT
                CONF_SECTION *cs;
 
                cs = cf_section_find(conf, "validation", CF_IDENT_ANY);
                if (!cs) {
                        cf_log_err(conf, "Missing validation section");
                        return -1;
                }
 
                if (rlm_yubikey_ykclient_init(cs, inst) < 0) {
                        return -1;
                }
#else
                cf_log_err(conf, "Requires libykclient for OTP validation against Yubicloud servers");
                return -1;
#endif
        }
 
        return 0;
}
 
#ifdef HAVE_YKCLIENT
static int mod_detach(module_detach_ctx_t const *mctx)
{
        rlm_yubikey_ykclient_detach(talloc_get_type_abort(mctx->mi->data, rlm_yubikey_t));
        return 0;
}
#endif
 
static int CC_HINT(nonnull) otp_string_valid(rlm_yubikey_t const *inst, char const *otp, size_t len)
{
        size_t i;
 
        for (i = inst->id_len; i < len; i++) {
                if (!is_modhex(otp[i])) return -i;
        }
 
        return 1;
}
 
 
/*
 *      Find the named user in this modules database.  Create the set
 *      of attribute-value pairs to check and reply with for this user
 *      from the database. The authentication code only needs to check
 *      the password, the rest is done here.
 */
static unlang_action_t CC_HINT(nonnull) mod_authorize(unlang_result_t *p_result, module_ctx_t const *mctx, request_t *request)
{
        rlm_yubikey_t const     *inst = talloc_get_type_abort_const(mctx->mi->data, rlm_yubikey_t);
        char const              *passcode;
        size_t                  len;
        fr_pair_t               *vp, *password;
        char const              *otp;
        size_t                  password_len;
        int                     ret;
 
        /*
         *      Can't do yubikey auth if there's no password.
         */
        password = fr_pair_find_by_da(&request->request_pairs, NULL, attr_user_password);
        if (!password) {
                /*
                 *      Don't print out debugging messages if we know
                 *      they're useless.
                 */
                if ((request->proto_dict == dict_radius) && request->packet->code != FR_RADIUS_CODE_ACCESS_CHALLENGE) {
                        RDEBUG2("No cleartext password in the request. Can't do Yubikey authentication");
                }
 
                RETURN_UNLANG_NOOP;
        }
 
        passcode = password->vp_strvalue;
        len = password->vp_length;
 
        /*
         *      Now see if the passcode is the correct length (in its raw
         *      modhex encoded form).
         *
         *      <public_id (6-16 bytes)> + <aes-block (32 bytes)>
         *
         */
        if (len < (inst->id_len + YUBIKEY_TOKEN_LEN)) {
                RDEBUG2("User-Password value is not the correct length, expected at least %u bytes, got %zu bytes",
                        inst->id_len + YUBIKEY_TOKEN_LEN, len);
                RETURN_UNLANG_NOOP;
        }
 
        password_len = (len - (inst->id_len + YUBIKEY_TOKEN_LEN));
        otp = passcode + password_len;
        ret = otp_string_valid(inst, otp, (inst->id_len + YUBIKEY_TOKEN_LEN));
        if (ret <= 0) {
                if (RDEBUG_ENABLED3) {
                        RDMARKER(otp, -(ret), "User-Password (aes-block) value contains non modhex chars");
                } else {
                        RDEBUG2("User-Password (aes-block) value contains non modhex chars");
                }
                RETURN_UNLANG_NOOP;
        }
 
        /* May be a concatenation, check the last 32 bytes are modhex */
        if (inst->split) {
                /*
                 *      Insert a new request attribute just containing the OTP
                 *      portion.
                 */
                MEM(pair_update_request(&vp, attr_yubikey_otp) >= 0);
                fr_pair_value_strdup(vp, otp, password->vp_tainted);
 
                /*
                 *      Replace the existing string buffer for the password
                 *      attribute with one just containing the password portion.
                 */
                MEM(fr_pair_value_bstr_realloc(password, NULL, password_len) == 0);
 
                RDEBUG2("request.%pP", vp);
                RDEBUG2("request.%pP", password);
 
                /*
                 *      So the ID split code works on the non password portion.
                 */
                passcode = vp->vp_strvalue;
        }
 
        /*
         *      Split out the Public ID in case another module in authorize
         *      needs to verify it's associated with the user.
         *
         *      It's left up to the user if they want to decode it or not.
         */
        if (inst->id_len) {
                MEM(pair_update_request(&vp, attr_yubikey_public_id) >= 0);
                fr_pair_value_bstrndup(vp, passcode, inst->id_len, true);
                RDEBUG2("request.%pP", vp);
        }
 
        if (!inst->auth_type) {
                WARN("No 'authenticate %s {...}' section or 'Auth-Type = %s' set.  Cannot setup Yubikey authentication",
                     mctx->mi->name, mctx->mi->name);
                RETURN_UNLANG_NOOP;
        }
 
        if (!module_rlm_section_type_set(request, attr_auth_type, inst->auth_type)) RETURN_UNLANG_NOOP;
 
        RETURN_UNLANG_OK;
}
 
 
/*
 *      Authenticate the user with the given password.
 */
static unlang_action_t CC_HINT(nonnull) mod_authenticate(unlang_result_t *p_result, module_ctx_t const *mctx, request_t *request)
{
        rlm_yubikey_t const     *inst = talloc_get_type_abort_const(mctx->mi->data, rlm_yubikey_t);
        char const              *passcode = NULL;
        fr_pair_t const         *vp;
        size_t                  len;
        int                     ret;
 
        p_result->rcode = RLM_MODULE_NOOP;
 
        vp = fr_pair_find_by_da_nested(&request->request_pairs, NULL, attr_yubikey_otp);
        if (!vp) {
                RDEBUG2("No Yubikey-OTP attribute found, falling back to User-Password");
                /*
                 *      Can't do yubikey auth if there's no password.
                 */
                vp = fr_pair_find_by_da(&request->request_pairs, NULL, attr_user_password);
                if (!vp) {
                        REDEBUG("No User-Password in the request. Can't do Yubikey authentication");
                        RETURN_UNLANG_INVALID;
                }
        }
 
        passcode = vp->vp_strvalue;
        len = vp->vp_length;
 
        /*
         *      Verify the passcode is the correct length (in its raw
         *      modhex encoded form).
         *
         *      <public_id (6-16 bytes)> + <aes-block (32 bytes)>
         */
        if (len != (inst->id_len + YUBIKEY_TOKEN_LEN)) {
                REDEBUG("%s value is not the correct length, expected bytes %u, got bytes %zu",
                        vp->da->name, inst->id_len + YUBIKEY_TOKEN_LEN, len);
                RETURN_UNLANG_INVALID;
        }
 
        ret = otp_string_valid(inst, passcode, (inst->id_len + YUBIKEY_TOKEN_LEN));
        if (ret <= 0) {
                if (RDEBUG_ENABLED3) {
                        REMARKER(passcode, -ret, "Passcode (aes-block) value contains non modhex chars");
                } else {
                        RERROR("Passcode (aes-block) value contains non modhex chars");
                }
                RETURN_UNLANG_INVALID;
        }
 
#ifdef HAVE_YUBIKEY
        if (inst->decrypt) {
 
                rlm_yubikey_decrypt(p_result, mctx, request, passcode);
                if (p_result->rcode != RLM_MODULE_OK) return UNLANG_ACTION_CALCULATE_RESULT;
                /* Fall-Through to doing ykclient auth in addition to local auth */
        }
#endif
 
#ifdef HAVE_YKCLIENT
        if (inst->validate) return rlm_yubikey_validate(p_result, mctx, request, passcode);
#endif
        return UNLANG_ACTION_CALCULATE_RESULT;
}
 
/*
 *      The module name should be the only globally exported symbol.
 *      That is, everything else should be 'static'.
 *
 *      If the module needs to temporarily modify it's instantiation
 *      data, the type should be changed to MODULE_TYPE_THREAD_UNSAFE.
 *      The server will then take care of ensuring that the module
 *      is single-threaded.
 */
extern module_rlm_t rlm_yubikey;
module_rlm_t rlm_yubikey = {
        .common = {
                .magic          = MODULE_MAGIC_INIT,
                .name           = "yubikey",
                .inst_size      = sizeof(rlm_yubikey_t),
                .onload         = mod_load,
                .unload         = mod_unload,
                .config         = module_config,
#ifndef HAVE_YUBIKEY
                .bootstrap      = mod_bootstrap,
#endif
                .instantiate    = mod_instantiate,
#ifdef HAVE_YKCLIENT
                .detach         = mod_detach,
#endif
        },
        .method_group = {
                .bindings = (module_method_binding_t[]){
                        { .section = SECTION_NAME("authenticate", CF_IDENT_ANY), .method = mod_authenticate },
                        { .section = SECTION_NAME("recv", "Access-Request"), .method = mod_authorize },
                        MODULE_BINDING_TERMINATOR
                }
        }
};