kdc/cjwt_token_validator.c

   1 /*
   2  * Copyright (c) 2019 Kungliga Tekniska Högskolan
   3  * (Royal Institute of Technology, Stockholm, Sweden).
   4  * All rights reserved.
   5  *
   6  * Redistribution and use in source and binary forms, with or without
   7  * modification, are permitted provided that the following conditions
   8  * are met:
   9  *
  10  * 1. Redistributions of source code must retain the above copyright
  11  *    notice, this list of conditions and the following disclaimer.
  12  *
  13  * 2. Redistributions in binary form must reproduce the above copyright
  14  *    notice, this list of conditions and the following disclaimer in the
  15  *    documentation and/or other materials provided with the distribution.
  16  *
  17  * 3. Neither the name of the Institute nor the names of its contributors
  18  *    may be used to endorse or promote products derived from this software
  19  *    without specific prior written permission.
  20  *
  21  * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
  22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
  25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  31  * SUCH DAMAGE.
  32  */
  33
  34 /*
  35  * This is a plugin by which bx509d can validate JWT Bearer tokens using the
  36  * cjwt library.
  37  *
  38  * Configuration:
  39  *
  40  *  [kdc]
  41  *      realm = {
  42  *          A.REALM.NAME = {
  43  *              cjwt_jqk = PATH-TO-JWK-PEM-FILE
  44  *          }
  45  *      }
  46  *
  47  * where AUDIENCE-FOR-KDC is the value of the "audience" (i.e., the target) of
  48  * the token.
  49  */
  50
  51 #include <config.h>
  52 #include <errno.h>
  53 #include <stdio.h>
  54 #include <string.h>
  55 #include <string.h>
  56 #include <heimbase.h>
  57 #include <krb5.h>
  58 #include <common_plugin.h>
  59 #include <hdb.h>
  60 #include <roken.h>
  61 #include <token_validator_plugin.h>
  62 #include <cjwt/cjwt.h>
  63 #ifdef HAVE_CJSON
  64 #include <cJSON.h>
  65 #endif
  66
  67 static const char *
  68 get_kv(krb5_context context, const char *realm, const char *k, const char *k2)
  69 {
  70     return krb5_config_get_string(context, NULL, "bx509", "realms", realm,
  71                                   k, k2, NULL);
  72 }
  73
  74 static krb5_error_code
  75 get_issuer_pubkeys(krb5_context context,
  76                    const char *realm,
  77                    krb5_data *previous,
  78                    krb5_data *current,
  79                    krb5_data *next)
  80 {
  81     krb5_error_code save_ret = 0;
  82     krb5_error_code ret;
  83     const char *v;
  84     size_t nkeys = 0;
  85
  86     previous->data = current->data = next->data = 0;
  87     previous->length = current->length = next->length = 0;
  88
  89     if ((v = get_kv(context, realm, "cjwt_jwk_next", NULL)) &&
  90         (++nkeys) &&
  91         (ret = rk_undumpdata(v, &next->data, &next->length)))
  92         save_ret = ret;
  93     if ((v = get_kv(context, realm, "cjwt_jwk_previous", NULL)) &&
  94         (++nkeys) &&
  95         (ret = rk_undumpdata(v, &previous->data, &previous->length)) &&
  96         save_ret == 0)
  97         save_ret = ret;
  98     if ((v = get_kv(context, realm, "cjwt_jwk_current", NULL)) &&
  99         (++nkeys) &&
 100         (ret = rk_undumpdata(v, &current->data, &current->length)) &&
 101         save_ret == 0)
 102         save_ret = ret;
 103     if (nkeys == 0)
 104         krb5_set_error_message(context, EINVAL, "jwk issuer key not specified in "
 105                                "[bx509]->realm->%s->cjwt_jwk_{previous,current,next}",
 106                                realm);
 107     if (!previous->length && !current->length && !next->length)
 108         krb5_set_error_message(context, save_ret,
 109                                "Could not read jwk issuer public key files");
 110     if (current->length && current->length == next->length &&
 111         memcmp(current->data, next->data, next->length) == 0) {
 112         free(next->data);
 113         next->data = 0;
 114         next->length = 0;
 115     }
 116     if (current->length && current->length == previous->length &&
 117         memcmp(current->data, previous->data, previous->length) == 0) {
 118         free(previous->data);
 119         previous->data = 0;
 120         previous->length = 0;
 121     }
 122
 123     if (previous->data == NULL && current->data == NULL && next->data == NULL)
 124         return krb5_set_error_message(context, ENOENT, "No JWKs found"),
 125                ENOENT;
 126     return 0;
 127 }
 128
 129 static krb5_error_code
 130 check_audience(krb5_context context,
 131                const char *realm,
 132                cjwt_t *jwt,
 133                const char * const *audiences,
 134                size_t naudiences)
 135 {
 136     size_t i, k;
 137
 138     if (!jwt->aud) {
 139         krb5_set_error_message(context, EACCES, "JWT bearer token has no "
 140                                "audience");
 141         return EACCES;
 142     }
 143     for (i = 0; i < jwt->aud->count; i++)
 144         for (k = 0; k < naudiences; k++)
 145             if (strcasecmp(audiences[k], jwt->aud->names[i]) == 0)
 146                 return 0;
 147     krb5_set_error_message(context, EACCES, "JWT bearer token's audience "
 148                            "does not match any expected audience");
 149     return EACCES;
 150 }
 151
 152 static krb5_error_code
 153 get_princ(krb5_context context,
 154           const char *realm,
 155           cjwt_t *jwt,
 156           krb5_principal *actual_principal)
 157 {
 158     krb5_error_code ret;
 159     const char *force_realm = NULL;
 160     const char *domain;
 161
 162 #ifdef HAVE_CJSON
 163     if (jwt->private_claims) {
 164         cJSON *jval;
 165
 166         if ((jval = cJSON_GetObjectItem(jwt->private_claims, "authz_sub")))
 167             return krb5_parse_name(context, jval->valuestring, actual_principal);
 168     }
 169 #endif
 170
 171     if (jwt->sub == NULL) {
 172         krb5_set_error_message(context, EACCES, "JWT token lacks 'sub' "
 173                                "(subject name)!");
 174         return EACCES;
 175     }
 176     if ((domain = strchr(jwt->sub, '@'))) {
 177         force_realm = get_kv(context, realm, "cjwt_force_realm", ++domain);
 178         ret = krb5_parse_name(context, jwt->sub, actual_principal);
 179     } else {
 180         ret = krb5_parse_name_flags(context, jwt->sub,
 181                                     KRB5_PRINCIPAL_PARSE_NO_REALM,
 182                                     actual_principal);
 183     }
 184     if (ret)
 185         krb5_set_error_message(context, ret, "JWT token 'sub' not a valid "
 186                                "principal name: %s", jwt->sub);
 187     else if (force_realm)
 188         ret = krb5_principal_set_realm(context, *actual_principal, realm);
 189     else if (domain == NULL)
 190         ret = krb5_principal_set_realm(context, *actual_principal, realm);
 191     /* else leave the domain as the realm */
 192     return ret;
 193 }
 194
 195 static KRB5_LIB_CALL krb5_error_code
 196 validate(void *ctx,
 197          krb5_context context,
 198          const char *realm,
 199          const char *token_type,
 200          krb5_data *token,
 201          const char * const *audiences,
 202          size_t naudiences,
 203          krb5_boolean *result,
 204          krb5_principal *actual_principal,
 205          krb5_times *token_times)
 206 {
 207     heim_octet_string jwk_previous;
 208     heim_octet_string jwk_current;
 209     heim_octet_string jwk_next;
 210     cjwt_t *jwt = NULL;
 211     char *tokstr = NULL;
 212     char *defrealm = NULL;
 213     int ret;
 214
 215     if (strcmp(token_type, "Bearer") != 0)
 216         return KRB5_PLUGIN_NO_HANDLE; /* Not us */
 217
 218     if ((tokstr = calloc(1, token->length + 1)) == NULL)
 219         return ENOMEM;
 220     memcpy(tokstr, token->data, token->length);
 221
 222     if (realm == NULL) {
 223         ret = krb5_get_default_realm(context, &defrealm);
 224         if (ret) {
 225             krb5_set_error_message(context, ret, "could not determine default "
 226                                    "realm");
 227             free(tokstr);
 228             return ret;
 229         }
 230         realm = defrealm;
 231     }
 232
 233     ret = get_issuer_pubkeys(context, realm, &jwk_previous, &jwk_current,
 234                              &jwk_next);
 235     if (ret) {
 236         free(defrealm);
 237         free(tokstr);
 238         return ret;
 239     }
 240
 241     if (jwk_current.length && jwk_current.data)
 242         ret = cjwt_decode(tokstr, 0, &jwt, jwk_current.data,
 243                           jwk_current.length);
 244     if (ret && jwk_next.length && jwk_next.data)
 245         ret = cjwt_decode(tokstr, 0, &jwt, jwk_next.data,
 246                             jwk_next.length);
 247     if (ret && jwk_previous.length && jwk_previous.data)
 248         ret = cjwt_decode(tokstr, 0, &jwt, jwk_previous.data,
 249                           jwk_previous.length);
 250     free(jwk_previous.data);
 251     free(jwk_current.data);
 252     free(jwk_next.data);
 253     jwk_previous.data = jwk_current.data = jwk_next.data = NULL;
 254     free(tokstr);
 255     tokstr = NULL;
 256     switch (ret) {
 257     case 0:
 258         if (jwt == NULL) {
 259             krb5_set_error_message(context, EINVAL, "JWT validation failed");
 260             free(defrealm);
 261             return EPERM;
 262         }
 263         if (jwt->header.alg == alg_none) {
 264             krb5_set_error_message(context, EINVAL, "JWT signature algorithm "
 265                                    "not supported");
 266             free(defrealm);
 267             return EPERM;
 268         }
 269         break;
 270     case -1:
 271         krb5_set_error_message(context, EINVAL, "invalid JWT format");
 272         free(defrealm);
 273         return EINVAL;
 274     case -2:
 275         krb5_set_error_message(context, EINVAL, "JWT signature validation "
 276                                "failed (wrong issuer?)");
 277         free(defrealm);
 278         return EPERM;
 279     default:
 280         krb5_set_error_message(context, ret, "misc token validation error");
 281         free(defrealm);
 282         return ret;
 283     }
 284
 285     /* Success; check audience */
 286     if ((ret = check_audience(context, realm, jwt, audiences, naudiences))) {
 287         cjwt_destroy(&jwt);
 288         free(defrealm);
 289         return EACCES;
 290     }
 291
 292     /* Success; extract principal name */
 293     if ((ret = get_princ(context, realm, jwt, actual_principal)) == 0) {
 294         token_times->authtime   = jwt->iat.tv_sec;
 295         token_times->starttime  = jwt->nbf.tv_sec;
 296         token_times->endtime    = jwt->exp.tv_sec;
 297         token_times->renew_till = jwt->exp.tv_sec;
 298         *result = TRUE;
 299     }
 300
 301     cjwt_destroy(&jwt);
 302     free(defrealm);
 303     return ret;
 304 }
 305
 306 static KRB5_LIB_CALL krb5_error_code
 307 hcjwt_init(krb5_context context, void **c)
 308 {
 309     *c = NULL;
 310     return 0;
 311 }
 312
 313 static KRB5_LIB_CALL void
 314 hcjwt_fini(void *c)
 315 {
 316 }
 317
 318 static krb5plugin_token_validator_ftable plug_desc =
 319     { 1, hcjwt_init, hcjwt_fini, validate };
 320
 321 static krb5plugin_token_validator_ftable *plugs[] = { &plug_desc };
 322
 323 static uintptr_t
 324 hcjwt_get_instance(const char *libname)
 325 {
 326     if (strcmp(libname, "krb5") == 0)
 327         return krb5_get_instance(libname);
 328     return 0;
 329 }
 330
 331 krb5_plugin_load_ft kdc_token_validator_plugin_load;
 332
 333 krb5_error_code KRB5_CALLCONV
 334 kdc_token_validator_plugin_load(heim_pcontext context,
 335                                 krb5_get_instance_func_t *get_instance,
 336                                 size_t *num_plugins,
 337                                 krb5_plugin_common_ftable_cp **plugins)
 338 {
 339     *get_instance = hcjwt_get_instance;
 340     *num_plugins = sizeof(plugs) / sizeof(plugs[0]);
 341     *plugins = (krb5_plugin_common_ftable_cp *)plugs;
 342     return 0;
 343 }