rlm_krb5.c

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/*
 *   This program 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: 9ef3cd59f854b0a5ee33d20c0aa65c03a7a0fb2b $
 * @file rlm_krb5.c
 * @brief Authenticate users, retrieving their TGT from a Kerberos V5 TDC.
 *
 * @copyright 2000,2006,2012-2013 The FreeRADIUS server project
 * @copyright 2013 Arran Cudbard-Bell (a.cudbardb@freeradius.org)
 * @copyright 2000 Nathan Neulinger (nneul@umr.edu)
 * @copyright 2000 Alan DeKok (aland@freeradius.org)
 */
RCSID("$Id: 9ef3cd59f854b0a5ee33d20c0aa65c03a7a0fb2b $")
 
#define LOG_PREFIX inst->name
 
#include <freeradius-devel/server/base.h>
#include <freeradius-devel/server/module_rlm.h>
#include "krb5.h"
 
#ifdef KRB5_IS_THREAD_SAFE
static const conf_parser_t reuse_krb5_config[] = {
        FR_SLAB_CONFIG_CONF_PARSER
        CONF_PARSER_TERMINATOR
};
#endif
 
static const conf_parser_t module_config[] = {
        { FR_CONF_OFFSET("keytab", rlm_krb5_t, keytabname) },
        { FR_CONF_OFFSET("service_principal", rlm_krb5_t, service_princ) },
#ifdef KRB5_IS_THREAD_SAFE
        { FR_CONF_OFFSET_SUBSECTION("reuse", 0, rlm_krb5_t, reuse, reuse_krb5_config) },
#endif
        CONF_PARSER_TERMINATOR
};
 
typedef struct {
        fr_value_box_t  username;
        fr_value_box_t  password;
} krb5_auth_call_env_t;
 
#ifdef KRB5_IS_THREAD_SAFE
static int mod_thread_instantiate(module_thread_inst_ctx_t const *mctx)
{
        rlm_krb5_t              *inst = talloc_get_type_abort(mctx->mi->data, rlm_krb5_t);
        rlm_krb5_thread_t       *t = talloc_get_type_abort(mctx->thread, rlm_krb5_thread_t);
 
        t->inst = inst;
        if (!(t->slab = krb5_slab_list_alloc(t, mctx->el, &inst->reuse, krb5_handle_init, NULL, inst, false, true))) {
                ERROR("Handle pool instantiation failed");
                return -1;
        }
 
        return 0;
}
 
static int mod_thread_detach(module_thread_inst_ctx_t const *mctx)
{
        rlm_krb5_thread_t       *t = talloc_get_type_abort(mctx->thread, rlm_krb5_thread_t);
        talloc_free(t->slab);
        return 0;
}
#endif
 
static int mod_detach(module_detach_ctx_t const *mctx)
{
        rlm_krb5_t *inst = talloc_get_type_abort(mctx->mi->data, rlm_krb5_t);
 
#ifndef HEIMDAL_KRB5
        talloc_free(inst->vic_options);
 
        if (inst->gic_options) krb5_get_init_creds_opt_free(inst->context, inst->gic_options);
        if (inst->server) krb5_free_principal(inst->context, inst->server);
#endif
 
        /* Don't free hostname, it's just a pointer into service_princ */
        talloc_free(inst->service);
 
        if (inst->context) krb5_free_context(inst->context);
 
        return 0;
}
 
static int mod_instantiate(module_inst_ctx_t const *mctx)
{
        rlm_krb5_t *inst = talloc_get_type_abort(mctx->mi->data, rlm_krb5_t);
        krb5_error_code ret;
#ifndef HEIMDAL_KRB5
        krb5_keytab keytab;
        char keytab_name[200];
        char *princ_name;
#endif
 
#ifdef HEIMDAL_KRB5
        DEBUG("Using Heimdal Kerberos library");
#else
        DEBUG("Using MIT Kerberos library");
#endif
 
 
        if (!krb5_is_thread_safe()) {
/*
 *      rlm_krb5 was built as threadsafe
 */
#ifdef KRB5_IS_THREAD_SAFE
                ERROR("Build time libkrb5 was threadsafe, but run time library claims not to be");
                ERROR("Modify runtime linker path (LD_LIBRARY_PATH on most systems), to prefer threadsafe libkrb5");
                return -1;
/*
 *      rlm_krb5 was not built as threadsafe
 */
#else
                fr_log(&default_log, L_WARN, __FILE__, __LINE__,
                       "libkrb5 is not threadsafe, recompile it with thread support enabled ("
#  ifdef HEIMDAL_KRB5
                       "--enable-pthread-support"
#  else
                       "--disable-thread-support=no"
#  endif
                       ")");
                WARN("rlm_krb5 will run in single threaded mode, performance may be degraded");
        } else {
                WARN("Build time libkrb5 was not threadsafe, but run time library claims to be");
                WARN("Reconfigure and recompile rlm_krb5 to enable thread support");
#endif
        }
 
        ret = krb5_init_context(&inst->context);
        if (ret) {
                ERROR("Context initialisation failed: %s", rlm_krb5_error(inst, NULL, ret));
 
                return -1;
        }
 
        /*
         *      Split service principal into service and host components
         *      they're needed to build the server principal in MIT,
         *      and to set the validation service in Heimdal.
         */
        if (inst->service_princ) {
                size_t len;
                /* Service principal appears to contain a host component */
                inst->hostname = strchr(inst->service_princ, '/');
                if (inst->hostname) {
                        len = (inst->hostname - inst->service_princ);
                        inst->hostname++;
                } else {
                        len = strlen(inst->service_princ);
                }
 
                if (len) {
                        inst->service = talloc_array(inst, char, (len + 1));
                        strlcpy(inst->service, inst->service_princ, len + 1);
                }
        }
 
#ifdef HEIMDAL_KRB5
        if (inst->hostname) DEBUG("Ignoring hostname component of service principal \"%s\", not "
                                  "needed/supported by Heimdal", inst->hostname);
#else
 
        /*
         *      Convert the service principal string to a krb5 principal.
         */
        ret = krb5_sname_to_principal(inst->context, inst->hostname, inst->service, KRB5_NT_SRV_HST, &(inst->server));
        if (ret) {
                ERROR("Failed parsing service principal: %s", rlm_krb5_error(inst, inst->context, ret));
 
                return -1;
        }
 
        ret = krb5_unparse_name(inst->context, inst->server, &princ_name);
        if (ret) {
                /* Uh? */
                ERROR("Failed constructing service principal string: %s", rlm_krb5_error(inst, inst->context, ret));
 
                return -1;
        }
 
        /*
         *      Not necessarily the same as the config item
         */
        DEBUG("Using service principal \"%s\"", princ_name);
        krb5_free_unparsed_name(inst->context, princ_name);
 
        /*
         *      Setup options for getting credentials and verifying them
         */
        ret = krb5_get_init_creds_opt_alloc(inst->context, &(inst->gic_options)); /* For some reason the 'init' version
                                                                                    of this function is deprecated */
        if (ret) {
                ERROR("Couldn't allocate initial credential options: %s", rlm_krb5_error(inst, inst->context, ret));
 
                return -1;
        }
 
        /*
         *      Perform basic checks on the keytab
         */
        ret = inst->keytabname ?
                krb5_kt_resolve(inst->context, inst->keytabname, &keytab) :
                krb5_kt_default(inst->context, &keytab);
        if (ret) {
                ERROR("Resolving keytab failed: %s", rlm_krb5_error(inst, inst->context, ret));
 
                return -1;
        }
 
        ret = krb5_kt_get_name(inst->context, keytab, keytab_name, sizeof(keytab_name));
        krb5_kt_close(inst->context, keytab);
        if (ret) {
                ERROR("Can't retrieve keytab name: %s", rlm_krb5_error(inst, inst->context, ret));
 
                return -1;
        }
 
        DEBUG("Using keytab \"%s\"", keytab_name);
 
        MEM(inst->vic_options = talloc_zero(inst, krb5_verify_init_creds_opt));
        krb5_verify_init_creds_opt_init(inst->vic_options);
        krb5_verify_init_creds_opt_set_ap_req_nofail(inst->vic_options, true);
#endif
 
#ifndef KRB5_IS_THREAD_SAFE
        inst->conn = krb5_mod_conn_create(inst, inst, fr_time_delta_wrap(0));
        if (!inst->conn) return -1;
#endif
        return 0;
}
 
/** Common function for transforming a User-Name string into a principal.
 *
 * @param[out] client Where to write the client principal.
 * @param[in] inst of rlm_krb5.
 * @param[in] request Current request.
 * @param[in] context Kerberos context.
 * @param[in] env call env data containing username.
 */
static rlm_rcode_t krb5_parse_user(krb5_principal *client, KRB5_UNUSED rlm_krb5_t const *inst, request_t *request,
                                   krb5_context context, krb5_auth_call_env_t *env)
{
        krb5_error_code ret;
        char *princ_name;
 
        ret = krb5_parse_name(context, env->username.vb_strvalue, client);
        if (ret) {
                REDEBUG("Failed parsing username as principal: %s", rlm_krb5_error(inst, context, ret));
 
                return RLM_MODULE_FAIL;
        }
 
        krb5_unparse_name(context, *client, &princ_name);
        RDEBUG2("Using client principal \"%s\"", princ_name);
#ifdef HEIMDAL_KRB5
        free(princ_name);
#else
        krb5_free_unparsed_name(context, princ_name);
#endif
        return RLM_MODULE_OK;
}
 
/** Log error message and return appropriate rcode
 *
 * Translate kerberos error codes into return codes.
 * @param inst of rlm_krb5.
 * @param request Current request.
 * @param ret code from kerberos.
 * @param conn used in the last operation.
 */
static rlm_rcode_t krb5_process_error(rlm_krb5_t const *inst, request_t *request, rlm_krb5_handle_t *conn, int ret)
{
        fr_assert(ret != 0);
 
        if (!fr_cond_assert(inst)) return RLM_MODULE_FAIL;
        if (!fr_cond_assert(conn)) return RLM_MODULE_FAIL;      /* Silences warnings */
 
        switch (ret) {
        case KRB5_LIBOS_BADPWDMATCH:
        case KRB5KRB_AP_ERR_BAD_INTEGRITY:
                REDEBUG("Provided password was incorrect (%i): %s", ret, rlm_krb5_error(inst, conn->context, ret));
                return RLM_MODULE_REJECT;
 
        case KRB5KDC_ERR_KEY_EXP:
        case KRB5KDC_ERR_CLIENT_REVOKED:
        case KRB5KDC_ERR_SERVICE_REVOKED:
                REDEBUG("Account has been locked out (%i): %s", ret, rlm_krb5_error(inst, conn->context, ret));
                return RLM_MODULE_DISALLOW;
 
        case KRB5KDC_ERR_C_PRINCIPAL_UNKNOWN:
                RDEBUG2("User not found (%i): %s", ret, rlm_krb5_error(inst, conn->context, ret));
                return RLM_MODULE_NOTFOUND;
 
        default:
                REDEBUG("Error verifying credentials (%i): %s", ret, rlm_krb5_error(inst, conn->context, ret));
                return RLM_MODULE_FAIL;
        }
}
 
#ifdef HEIMDAL_KRB5
 
/*
 *      Validate user/pass (Heimdal)
 */
static unlang_action_t CC_HINT(nonnull) mod_authenticate(unlang_result_t *p_result, module_ctx_t const *mctx, request_t *request)
{
        krb5_auth_call_env_t    *env = talloc_get_type_abort(mctx->env_data, krb5_auth_call_env_t);
        rlm_krb5_t const        *inst = talloc_get_type_abort_const(mctx->mi->data, rlm_krb5_t);
#  ifdef KRB5_IS_THREAD_SAFE
        rlm_krb5_thread_t       *t = talloc_get_type_abort(mctx->thread, rlm_krb5_thread_t);
#  endif
        rlm_rcode_t             rcode;
        krb5_error_code         ret;
        rlm_krb5_handle_t       *conn;
        krb5_principal          client = NULL;
 
        /*
         *      Make sure the supplied password isn't empty
         */
        if (env->password.vb_length == 0) {
                REDEBUG("User-Password must not be empty");
                RETURN_UNLANG_INVALID;
        }
 
        /*
         *      Log the password
         */
        if (RDEBUG_ENABLED3) {
                RDEBUG("Login attempt with password \"%pV\"", &env->password);
        } else {
                RDEBUG2("Login attempt with password");
        }
 
#  ifdef KRB5_IS_THREAD_SAFE
        conn = krb5_slab_reserve(t->slab);
        if (!conn) RETURN_UNLANG_FAIL;
#  else
        conn = inst->conn;
#  endif
 
        rcode = krb5_parse_user(&client, inst, request, conn->context, env);
        if (rcode != RLM_MODULE_OK) goto cleanup;
 
        /*
         *      Verify the user, using the options we set in instantiate
         */
        ret = krb5_verify_user_opt(conn->context, client, env->password.vb_strvalue, &conn->options);
        if (ret) {
                rcode = krb5_process_error(inst, request, conn, ret);
                goto cleanup;
        }
 
        /*
         *      krb5_verify_user_opt adds the credentials to the ccache
         *      we specified with krb5_verify_opt_set_ccache.
         *
         *      To make sure we don't accumulate thousands of sets of
         *      credentials, remove them again here.
         *
         * @todo This should definitely be optional, which means writing code for the MIT
         *       variant as well.
         */
        {
                krb5_cc_cursor cursor;
                krb5_creds cred;
 
                krb5_cc_start_seq_get(conn->context, conn->ccache, &cursor);
                for (ret = krb5_cc_next_cred(conn->context, conn->ccache, &cursor, &cred);
                     ret == 0;
                     ret = krb5_cc_next_cred(conn->context, conn->ccache, &cursor, &cred)) {
                     krb5_cc_remove_cred(conn->context, conn->ccache, 0, &cred);
                }
                krb5_cc_end_seq_get(conn->context, conn->ccache, &cursor);
        }
 
cleanup:
        if (client) {
                krb5_free_principal(conn->context, client);
        }
 
#  ifdef KRB5_IS_THREAD_SAFE
        krb5_slab_release(conn);
#  endif
        RETURN_UNLANG_RCODE(rcode);
}
 
#else  /* HEIMDAL_KRB5 */
 
/*
 *  Validate userid/passwd (MIT)
 */
static unlang_action_t CC_HINT(nonnull) mod_authenticate(unlang_result_t *p_result, module_ctx_t const *mctx, request_t *request)
{
        krb5_auth_call_env_t    *env = talloc_get_type_abort(mctx->env_data, krb5_auth_call_env_t);
        rlm_krb5_t const        *inst = talloc_get_type_abort_const(mctx->mi->data, rlm_krb5_t);
#  ifdef KRB5_IS_THREAD_SAFE
        rlm_krb5_thread_t       *t = talloc_get_type_abort(mctx->thread, rlm_krb5_thread_t);
#  endif
        rlm_rcode_t             rcode;
        krb5_error_code         ret;
 
        rlm_krb5_handle_t       *conn;
 
        krb5_principal          client = NULL;  /* actually a pointer value */
        krb5_creds              init_creds;
 
        /*
         *      Make sure the supplied password isn't empty
         */
        if (env->password.vb_length == 0) {
                REDEBUG("User-Password must not be empty");
                RETURN_UNLANG_INVALID;
        }
 
        /*
         *      Log the password
         */
        if (RDEBUG_ENABLED3) {
                RDEBUG("Login attempt with password \"%pV\"", &env->password);
        } else {
                RDEBUG2("Login attempt with password");
        }
 
#  ifdef KRB5_IS_THREAD_SAFE
        conn = krb5_slab_reserve(t->slab);
        if (!conn) RETURN_UNLANG_FAIL;
#  else
        conn = inst->conn;
#  endif
 
        /*
         *      Zero out local storage
         */
        memset(&init_creds, 0, sizeof(init_creds));
 
        /*
         *      Check we have all the required VPs, and convert the username
         *      into a principal.
         */
        rcode = krb5_parse_user(&client, inst, request, conn->context, env);
        if (rcode != RLM_MODULE_OK) goto cleanup;
 
        /*
         *      Retrieve the TGT from the TGS/KDC and check we can decrypt it.
         */
        RDEBUG2("Retrieving and decrypting TGT");
        ret = krb5_get_init_creds_password(conn->context, &init_creds, client, UNCONST(char *, env->password.vb_strvalue),
                                           NULL, NULL, 0, NULL, inst->gic_options);
        if (ret) {
                rcode = krb5_process_error(inst, request, conn, ret);
                goto cleanup;
        }
 
        RDEBUG2("Attempting to authenticate against service principal");
        ret = krb5_verify_init_creds(conn->context, &init_creds, inst->server, conn->keytab, NULL, inst->vic_options);
        if (ret) rcode = krb5_process_error(inst, request, conn, ret);
 
cleanup:
        if (client) krb5_free_principal(conn->context, client);
        krb5_free_cred_contents(conn->context, &init_creds);
 
#  ifdef KRB5_IS_THREAD_SAFE
        krb5_slab_release(conn);
#  endif
        RETURN_UNLANG_RCODE(rcode);
}
 
#endif /* MIT_KRB5 */
 
static const call_env_method_t krb5_auth_call_env = {
        FR_CALL_ENV_METHOD_OUT(krb5_auth_call_env_t),
        .env = (call_env_parser_t[]) {
                { FR_CALL_ENV_OFFSET("username", FR_TYPE_STRING, CALL_ENV_FLAG_REQUIRED| CALL_ENV_FLAG_BARE_WORD_ATTRIBUTE, krb5_auth_call_env_t, username),
                        .pair.dflt = "User-Name", .pair.dflt_quote = T_BARE_WORD },
                { FR_CALL_ENV_OFFSET("password", FR_TYPE_STRING, CALL_ENV_FLAG_SECRET | CALL_ENV_FLAG_REQUIRED| CALL_ENV_FLAG_BARE_WORD_ATTRIBUTE, krb5_auth_call_env_t, password),
                        .pair.dflt = "User-Password", .pair.dflt_quote = T_BARE_WORD },
                CALL_ENV_TERMINATOR
        }
};
 
extern module_rlm_t rlm_krb5;
module_rlm_t rlm_krb5 = {
        .common = {
                .magic          = MODULE_MAGIC_INIT,
                .name           = "krb5",
                /*
                 *      FIXME - Probably want a global mutex created on mod_load
                 */
#ifndef KRB5_IS_THREAD_SAFE
                .flags          = MODULE_TYPE_THREAD_UNSAFE,
#else
                .thread_inst_size       = sizeof(rlm_krb5_thread_t),
                .thread_instantiate     = mod_thread_instantiate,
                .thread_detach          = mod_thread_detach,
#endif
                .inst_size      = sizeof(rlm_krb5_t),
                .config         = module_config,
                .instantiate    = mod_instantiate,
                .detach         = mod_detach
        },
        .method_group = {
                .bindings = (module_method_binding_t[]){
                        { .section = SECTION_NAME("authenticate", CF_IDENT_ANY), .method = mod_authenticate, .method_env = &krb5_auth_call_env },
                        MODULE_BINDING_TERMINATOR
                }
        }
};