crypto/asymmetric_keys/x509_public_key.c

   1 /* Instantiate a public key crypto key from an X.509 Certificate
   2  *
   3  * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
   4  * Written by David Howells (dhowells@redhat.com)
   5  *
   6  * This program is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU General Public Licence
   8  * as published by the Free Software Foundation; either version
   9  * 2 of the Licence, or (at your option) any later version.
  10  */
  11
  12 #define pr_fmt(fmt) "X.509: "fmt
  13 #include <linux/module.h>
  14 #include <linux/kernel.h>
  15 #include <linux/slab.h>
  16 #include <linux/err.h>
  17 #include <linux/mpi.h>
  18 #include <linux/asn1_decoder.h>
  19 #include <keys/asymmetric-subtype.h>
  20 #include <keys/asymmetric-parser.h>
  21 #include <keys/system_keyring.h>
  22 #include <crypto/hash.h>
  23 #include "asymmetric_keys.h"
  24 #include "public_key.h"
  25 #include "x509_parser.h"
  26
  27 static bool use_builtin_keys;
  28 static struct asymmetric_key_id *ca_keyid;
  29
  30 #ifndef MODULE
  31 static struct {
  32         struct asymmetric_key_id id;
  33         unsigned char data[10];
  34 } cakey;
  35
  36 static int __init ca_keys_setup(char *str)
  37 {
  38         if (!str)               /* default system keyring */
  39                 return 1;
  40
  41         if (strncmp(str, "id:", 3) == 0) {
  42                 struct asymmetric_key_id *p = &cakey.id;
  43                 size_t hexlen = (strlen(str) - 3) / 2;
  44                 int ret;
  45
  46                 if (hexlen == 0 || hexlen > sizeof(cakey.data)) {
  47                         pr_err("Missing or invalid ca_keys id\n");
  48                         return 1;
  49                 }
  50
  51                 ret = __asymmetric_key_hex_to_key_id(str + 3, p, hexlen);
  52                 if (ret < 0)
  53                         pr_err("Unparsable ca_keys id hex string\n");
  54                 else
  55                         ca_keyid = p;   /* owner key 'id:xxxxxx' */
  56         } else if (strcmp(str, "builtin") == 0) {
  57                 use_builtin_keys = true;
  58         }
  59
  60         return 1;
  61 }
  62 __setup("ca_keys=", ca_keys_setup);
  63 #endif
  64
  65 /**
  66  * x509_request_asymmetric_key - Request a key by X.509 certificate params.
  67  * @keyring: The keys to search.
  68  * @id: The issuer & serialNumber to look for or NULL.
  69  * @skid: The subjectKeyIdentifier to look for or NULL.
  70  * @partial: Use partial match if true, exact if false.
  71  *
  72  * Find a key in the given keyring by identifier.  The preferred identifier is
  73  * the issuer + serialNumber and the fallback identifier is the
  74  * subjectKeyIdentifier.  If both are given, the lookup is by the former, but
  75  * the latter must also match.
  76  */
  77 struct key *x509_request_asymmetric_key(struct key *keyring,
  78                                         const struct asymmetric_key_id *id,
  79                                         const struct asymmetric_key_id *skid,
  80                                         bool partial)
  81 {
  82         struct key *key;
  83         key_ref_t ref;
  84         const char *lookup;
  85         char *req, *p;
  86         int len;
  87
  88         if (id) {
  89                 lookup = id->data;
  90                 len = id->len;
  91         } else {
  92                 lookup = skid->data;
  93                 len = skid->len;
  94         }
  95
  96         /* Construct an identifier "id:<keyid>". */
  97         p = req = kmalloc(2 + 1 + len * 2 + 1, GFP_KERNEL);
  98         if (!req)
  99                 return ERR_PTR(-ENOMEM);
 100
 101         if (partial) {
 102                 *p++ = 'i';
 103                 *p++ = 'd';
 104         } else {
 105                 *p++ = 'e';
 106                 *p++ = 'x';
 107         }
 108         *p++ = ':';
 109         p = bin2hex(p, lookup, len);
 110         *p = 0;
 111
 112         pr_debug("Look up: \"%s\"\n", req);
 113
 114         ref = keyring_search(make_key_ref(keyring, 1),
 115                              &key_type_asymmetric, req);
 116         if (IS_ERR(ref))
 117                 pr_debug("Request for key '%s' err %ld\n", req, PTR_ERR(ref));
 118         kfree(req);
 119
 120         if (IS_ERR(ref)) {
 121                 switch (PTR_ERR(ref)) {
 122                         /* Hide some search errors */
 123                 case -EACCES:
 124                 case -ENOTDIR:
 125                 case -EAGAIN:
 126                         return ERR_PTR(-ENOKEY);
 127                 default:
 128                         return ERR_CAST(ref);
 129                 }
 130         }
 131
 132         key = key_ref_to_ptr(ref);
 133         if (id && skid) {
 134                 const struct asymmetric_key_ids *kids = asymmetric_key_ids(key);
 135                 if (!kids->id[1]) {
 136                         pr_debug("issuer+serial match, but expected SKID missing\n");
 137                         goto reject;
 138                 }
 139                 if (!asymmetric_key_id_same(skid, kids->id[1])) {
 140                         pr_debug("issuer+serial match, but SKID does not\n");
 141                         goto reject;
 142                 }
 143         }
 144
 145         pr_devel("<==%s() = 0 [%x]\n", __func__, key_serial(key));
 146         return key;
 147
 148 reject:
 149         key_put(key);
 150         return ERR_PTR(-EKEYREJECTED);
 151 }
 152 EXPORT_SYMBOL_GPL(x509_request_asymmetric_key);
 153
 154 /*
 155  * Set up the signature parameters in an X.509 certificate.  This involves
 156  * digesting the signed data and extracting the signature.
 157  */
 158 int x509_get_sig_params(struct x509_certificate *cert)
 159 {
 160         struct crypto_shash *tfm;
 161         struct shash_desc *desc;
 162         size_t digest_size, desc_size;
 163         void *digest;
 164         int ret;
 165
 166         pr_devel("==>%s()\n", __func__);
 167
 168         if (cert->unsupported_crypto)
 169                 return -ENOPKG;
 170         if (cert->sig.rsa.s)
 171                 return 0;
 172
 173         cert->sig.rsa.s = mpi_read_raw_data(cert->raw_sig, cert->raw_sig_size);
 174         if (!cert->sig.rsa.s)
 175                 return -ENOMEM;
 176         cert->sig.nr_mpi = 1;
 177
 178         /* Allocate the hashing algorithm we're going to need and find out how
 179          * big the hash operational data will be.
 180          */
 181         tfm = crypto_alloc_shash(hash_algo_name[cert->sig.pkey_hash_algo], 0, 0);
 182         if (IS_ERR(tfm)) {
 183                 if (PTR_ERR(tfm) == -ENOENT) {
 184                         cert->unsupported_crypto = true;
 185                         return -ENOPKG;
 186                 }
 187                 return PTR_ERR(tfm);
 188         }
 189
 190         desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
 191         digest_size = crypto_shash_digestsize(tfm);
 192
 193         /* We allocate the hash operational data storage on the end of the
 194          * digest storage space.
 195          */
 196         ret = -ENOMEM;
 197         digest = kzalloc(ALIGN(digest_size, __alignof__(*desc)) + desc_size,
 198                          GFP_KERNEL);
 199         if (!digest)
 200                 goto error;
 201
 202         cert->sig.digest = digest;
 203         cert->sig.digest_size = digest_size;
 204
 205         desc = PTR_ALIGN(digest + digest_size, __alignof__(*desc));
 206         desc->tfm = tfm;
 207         desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
 208
 209         ret = crypto_shash_init(desc);
 210         if (ret < 0)
 211                 goto error;
 212         might_sleep();
 213         ret = crypto_shash_finup(desc, cert->tbs, cert->tbs_size, digest);
 214 error:
 215         crypto_free_shash(tfm);
 216         pr_devel("<==%s() = %d\n", __func__, ret);
 217         return ret;
 218 }
 219 EXPORT_SYMBOL_GPL(x509_get_sig_params);
 220
 221 /*
 222  * Check the signature on a certificate using the provided public key
 223  */
 224 int x509_check_signature(const struct public_key *pub,
 225                          struct x509_certificate *cert)
 226 {
 227         int ret;
 228
 229         pr_devel("==>%s()\n", __func__);
 230
 231         ret = x509_get_sig_params(cert);
 232         if (ret < 0)
 233                 return ret;
 234
 235         ret = public_key_verify_signature(pub, &cert->sig);
 236         if (ret == -ENOPKG)
 237                 cert->unsupported_crypto = true;
 238         pr_debug("Cert Verification: %d\n", ret);
 239         return ret;
 240 }
 241 EXPORT_SYMBOL_GPL(x509_check_signature);
 242
 243 /*
 244  * Check the new certificate against the ones in the trust keyring.  If one of
 245  * those is the signing key and validates the new certificate, then mark the
 246  * new certificate as being trusted.
 247  *
 248  * Return 0 if the new certificate was successfully validated, 1 if we couldn't
 249  * find a matching parent certificate in the trusted list and an error if there
 250  * is a matching certificate but the signature check fails.
 251  */
 252 static int x509_validate_trust(struct x509_certificate *cert,
 253                                struct key *trust_keyring)
 254 {
 255         struct key *key;
 256         int ret = 1;
 257
 258         if (!trust_keyring)
 259                 return -EOPNOTSUPP;
 260
 261         if (ca_keyid && !asymmetric_key_id_partial(cert->akid_skid, ca_keyid))
 262                 return -EPERM;
 263
 264         key = x509_request_asymmetric_key(trust_keyring,
 265                                           cert->akid_id, cert->akid_skid,
 266                                           false);
 267         if (!IS_ERR(key))  {
 268                 if (!use_builtin_keys
 269                     || test_bit(KEY_FLAG_BUILTIN, &key->flags))
 270                         ret = x509_check_signature(key->payload.data[asym_crypto],
 271                                                    cert);
 272                 key_put(key);
 273         }
 274         return ret;
 275 }
 276
 277 /*
 278  * Attempt to parse a data blob for a key as an X509 certificate.
 279  */
 280 static int x509_key_preparse(struct key_preparsed_payload *prep)
 281 {
 282         struct asymmetric_key_ids *kids;
 283         struct x509_certificate *cert;
 284         const char *q;
 285         size_t srlen, sulen;
 286         char *desc = NULL, *p;
 287         int ret;
 288
 289         cert = x509_cert_parse(prep->data, prep->datalen);
 290         if (IS_ERR(cert))
 291                 return PTR_ERR(cert);
 292
 293         pr_devel("Cert Issuer: %s\n", cert->issuer);
 294         pr_devel("Cert Subject: %s\n", cert->subject);
 295
 296         if (cert->pub->pkey_algo >= PKEY_ALGO__LAST ||
 297             cert->sig.pkey_algo >= PKEY_ALGO__LAST ||
 298             cert->sig.pkey_hash_algo >= PKEY_HASH__LAST ||
 299             !pkey_algo[cert->pub->pkey_algo] ||
 300             !pkey_algo[cert->sig.pkey_algo] ||
 301             !hash_algo_name[cert->sig.pkey_hash_algo]) {
 302                 ret = -ENOPKG;
 303                 goto error_free_cert;
 304         }
 305
 306         pr_devel("Cert Key Algo: %s\n", pkey_algo_name[cert->pub->pkey_algo]);
 307         pr_devel("Cert Valid period: %lld-%lld\n", cert->valid_from, cert->valid_to);
 308         pr_devel("Cert Signature: %s + %s\n",
 309                  pkey_algo_name[cert->sig.pkey_algo],
 310                  hash_algo_name[cert->sig.pkey_hash_algo]);
 311
 312         cert->pub->algo = pkey_algo[cert->pub->pkey_algo];
 313         cert->pub->id_type = PKEY_ID_X509;
 314
 315         /* Check the signature on the key if it appears to be self-signed */
 316         if ((!cert->akid_skid && !cert->akid_id) ||
 317             asymmetric_key_id_same(cert->skid, cert->akid_skid) ||
 318             asymmetric_key_id_same(cert->id, cert->akid_id)) {
 319                 ret = x509_check_signature(cert->pub, cert); /* self-signed */
 320                 if (ret < 0)
 321                         goto error_free_cert;
 322         } else if (!prep->trusted) {
 323                 ret = x509_validate_trust(cert, get_system_trusted_keyring());
 324                 if (ret)
 325                         ret = x509_validate_trust(cert, get_ima_mok_keyring());
 326                 if (!ret)
 327                         prep->trusted = 1;
 328         }
 329
 330         /* Propose a description */
 331         sulen = strlen(cert->subject);
 332         if (cert->raw_skid) {
 333                 srlen = cert->raw_skid_size;
 334                 q = cert->raw_skid;
 335         } else {
 336                 srlen = cert->raw_serial_size;
 337                 q = cert->raw_serial;
 338         }
 339
 340         ret = -ENOMEM;
 341         desc = kmalloc(sulen + 2 + srlen * 2 + 1, GFP_KERNEL);
 342         if (!desc)
 343                 goto error_free_cert;
 344         p = memcpy(desc, cert->subject, sulen);
 345         p += sulen;
 346         *p++ = ':';
 347         *p++ = ' ';
 348         p = bin2hex(p, q, srlen);
 349         *p = 0;
 350
 351         kids = kmalloc(sizeof(struct asymmetric_key_ids), GFP_KERNEL);
 352         if (!kids)
 353                 goto error_free_desc;
 354         kids->id[0] = cert->id;
 355         kids->id[1] = cert->skid;
 356
 357         /* We're pinning the module by being linked against it */
 358         __module_get(public_key_subtype.owner);
 359         prep->payload.data[asym_subtype] = &public_key_subtype;
 360         prep->payload.data[asym_key_ids] = kids;
 361         prep->payload.data[asym_crypto] = cert->pub;
 362         prep->description = desc;
 363         prep->quotalen = 100;
 364
 365         /* We've finished with the certificate */
 366         cert->pub = NULL;
 367         cert->id = NULL;
 368         cert->skid = NULL;
 369         desc = NULL;
 370         ret = 0;
 371
 372 error_free_desc:
 373         kfree(desc);
 374 error_free_cert:
 375         x509_free_certificate(cert);
 376         return ret;
 377 }
 378
 379 static struct asymmetric_key_parser x509_key_parser = {
 380         .owner  = THIS_MODULE,
 381         .name   = "x509",
 382         .parse  = x509_key_preparse,
 383 };
 384
 385 /*
 386  * Module stuff
 387  */
 388 static int __init x509_key_init(void)
 389 {
 390         return register_asymmetric_key_parser(&x509_key_parser);
 391 }
 392
 393 static void __exit x509_key_exit(void)
 394 {
 395         unregister_asymmetric_key_parser(&x509_key_parser);
 396 }
 397
 398 module_init(x509_key_init);
 399 module_exit(x509_key_exit);
 400
 401 MODULE_DESCRIPTION("X.509 certificate parser");
 402 MODULE_LICENSE("GPL");