crypto/asymmetric_keys/pkcs7_verify.c

   1 /* Verify the signature on a PKCS#7 message.
   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) "PKCS7: "fmt
  13 #include <linux/kernel.h>
  14 #include <linux/export.h>
  15 #include <linux/slab.h>
  16 #include <linux/err.h>
  17 #include <linux/asn1.h>
  18 #include <crypto/hash.h>
  19 #include "public_key.h"
  20 #include "pkcs7_parser.h"
  21
  22 /*
  23  * Digest the relevant parts of the PKCS#7 data
  24  */
  25 static int pkcs7_digest(struct pkcs7_message *pkcs7,
  26                         struct pkcs7_signed_info *sinfo)
  27 {
  28         struct crypto_shash *tfm;
  29         struct shash_desc *desc;
  30         size_t digest_size, desc_size;
  31         void *digest;
  32         int ret;
  33
  34         kenter(",%u,%u", sinfo->index, sinfo->sig.pkey_hash_algo);
  35
  36         if (sinfo->sig.pkey_hash_algo >= PKEY_HASH__LAST ||
  37             !hash_algo_name[sinfo->sig.pkey_hash_algo])
  38                 return -ENOPKG;
  39
  40         /* Allocate the hashing algorithm we're going to need and find out how
  41          * big the hash operational data will be.
  42          */
  43         tfm = crypto_alloc_shash(hash_algo_name[sinfo->sig.pkey_hash_algo],
  44                                  0, 0);
  45         if (IS_ERR(tfm))
  46                 return (PTR_ERR(tfm) == -ENOENT) ? -ENOPKG : PTR_ERR(tfm);
  47
  48         desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
  49         sinfo->sig.digest_size = digest_size = crypto_shash_digestsize(tfm);
  50
  51         ret = -ENOMEM;
  52         digest = kzalloc(ALIGN(digest_size, __alignof__(*desc)) + desc_size,
  53                          GFP_KERNEL);
  54         if (!digest)
  55                 goto error_no_desc;
  56
  57         desc = PTR_ALIGN(digest + digest_size, __alignof__(*desc));
  58         desc->tfm   = tfm;
  59         desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
  60
  61         /* Digest the message [RFC2315 9.3] */
  62         ret = crypto_shash_init(desc);
  63         if (ret < 0)
  64                 goto error;
  65         ret = crypto_shash_finup(desc, pkcs7->data, pkcs7->data_len, digest);
  66         if (ret < 0)
  67                 goto error;
  68         pr_devel("MsgDigest = [%*ph]\n", 8, digest);
  69
  70         /* However, if there are authenticated attributes, there must be a
  71          * message digest attribute amongst them which corresponds to the
  72          * digest we just calculated.
  73          */
  74         if (sinfo->authattrs) {
  75                 u8 tag;
  76
  77                 if (!sinfo->msgdigest) {
  78                         pr_warn("Sig %u: No messageDigest\n", sinfo->index);
  79                         ret = -EKEYREJECTED;
  80                         goto error;
  81                 }
  82
  83                 if (sinfo->msgdigest_len != sinfo->sig.digest_size) {
  84                         pr_debug("Sig %u: Invalid digest size (%u)\n",
  85                                  sinfo->index, sinfo->msgdigest_len);
  86                         ret = -EBADMSG;
  87                         goto error;
  88                 }
  89
  90                 if (memcmp(digest, sinfo->msgdigest, sinfo->msgdigest_len) != 0) {
  91                         pr_debug("Sig %u: Message digest doesn't match\n",
  92                                  sinfo->index);
  93                         ret = -EKEYREJECTED;
  94                         goto error;
  95                 }
  96
  97                 /* We then calculate anew, using the authenticated attributes
  98                  * as the contents of the digest instead.  Note that we need to
  99                  * convert the attributes from a CONT.0 into a SET before we
 100                  * hash it.
 101                  */
 102                 memset(digest, 0, sinfo->sig.digest_size);
 103
 104                 ret = crypto_shash_init(desc);
 105                 if (ret < 0)
 106                         goto error;
 107                 tag = ASN1_CONS_BIT | ASN1_SET;
 108                 ret = crypto_shash_update(desc, &tag, 1);
 109                 if (ret < 0)
 110                         goto error;
 111                 ret = crypto_shash_finup(desc, sinfo->authattrs,
 112                                          sinfo->authattrs_len, digest);
 113                 if (ret < 0)
 114                         goto error;
 115                 pr_devel("AADigest = [%*ph]\n", 8, digest);
 116         }
 117
 118         sinfo->sig.digest = digest;
 119         digest = NULL;
 120
 121 error:
 122         kfree(digest);
 123 error_no_desc:
 124         crypto_free_shash(tfm);
 125         kleave(" = %d", ret);
 126         return ret;
 127 }
 128
 129 /*
 130  * Find the key (X.509 certificate) to use to verify a PKCS#7 message.  PKCS#7
 131  * uses the issuer's name and the issuing certificate serial number for
 132  * matching purposes.  These must match the certificate issuer's name (not
 133  * subject's name) and the certificate serial number [RFC 2315 6.7].
 134  */
 135 static int pkcs7_find_key(struct pkcs7_message *pkcs7,
 136                           struct pkcs7_signed_info *sinfo)
 137 {
 138         struct x509_certificate *x509;
 139         unsigned certix = 1;
 140
 141         kenter("%u", sinfo->index);
 142
 143         for (x509 = pkcs7->certs; x509; x509 = x509->next, certix++) {
 144                 /* I'm _assuming_ that the generator of the PKCS#7 message will
 145                  * encode the fields from the X.509 cert in the same way in the
 146                  * PKCS#7 message - but I can't be 100% sure of that.  It's
 147                  * possible this will need element-by-element comparison.
 148                  */
 149                 if (!asymmetric_key_id_same(x509->id, sinfo->signing_cert_id))
 150                         continue;
 151                 pr_devel("Sig %u: Found cert serial match X.509[%u]\n",
 152                          sinfo->index, certix);
 153
 154                 if (x509->pub->pkey_algo != sinfo->sig.pkey_algo) {
 155                         pr_warn("Sig %u: X.509 algo and PKCS#7 sig algo don't match\n",
 156                                 sinfo->index);
 157                         continue;
 158                 }
 159
 160                 sinfo->signer = x509;
 161                 return 0;
 162         }
 163
 164         /* The relevant X.509 cert isn't found here, but it might be found in
 165          * the trust keyring.
 166          */
 167         pr_debug("Sig %u: Issuing X.509 cert not found (#%*phN)\n",
 168                  sinfo->index,
 169                  sinfo->signing_cert_id->len, sinfo->signing_cert_id->data);
 170         return 0;
 171 }
 172
 173 /*
 174  * Verify the internal certificate chain as best we can.
 175  */
 176 static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7,
 177                                   struct pkcs7_signed_info *sinfo)
 178 {
 179         struct x509_certificate *x509 = sinfo->signer, *p;
 180         struct asymmetric_key_id *auth;
 181         int ret;
 182
 183         kenter("");
 184
 185         for (p = pkcs7->certs; p; p = p->next)
 186                 p->seen = false;
 187
 188         for (;;) {
 189                 pr_debug("verify %s: %*phN\n",
 190                          x509->subject,
 191                          x509->raw_serial_size, x509->raw_serial);
 192                 x509->seen = true;
 193                 ret = x509_get_sig_params(x509);
 194                 if (ret < 0)
 195                         goto maybe_missing_crypto_in_x509;
 196
 197                 pr_debug("- issuer %s\n", x509->issuer);
 198                 if (x509->akid_id)
 199                         pr_debug("- authkeyid.id %*phN\n",
 200                                  x509->akid_id->len, x509->akid_id->data);
 201                 if (x509->akid_skid)
 202                         pr_debug("- authkeyid.skid %*phN\n",
 203                                  x509->akid_skid->len, x509->akid_skid->data);
 204
 205                 if ((!x509->akid_id && !x509->akid_skid) ||
 206                     strcmp(x509->subject, x509->issuer) == 0) {
 207                         /* If there's no authority certificate specified, then
 208                          * the certificate must be self-signed and is the root
 209                          * of the chain.  Likewise if the cert is its own
 210                          * authority.
 211                          */
 212                         pr_debug("- no auth?\n");
 213                         if (x509->raw_subject_size != x509->raw_issuer_size ||
 214                             memcmp(x509->raw_subject, x509->raw_issuer,
 215                                    x509->raw_issuer_size) != 0)
 216                                 return 0;
 217
 218                         ret = x509_check_signature(x509->pub, x509);
 219                         if (ret < 0)
 220                                 goto maybe_missing_crypto_in_x509;
 221                         x509->signer = x509;
 222                         pr_debug("- self-signed\n");
 223                         return 0;
 224                 }
 225
 226                 /* Look through the X.509 certificates in the PKCS#7 message's
 227                  * list to see if the next one is there.
 228                  */
 229                 auth = x509->akid_id;
 230                 if (auth) {
 231                         pr_debug("- want %*phN\n", auth->len, auth->data);
 232                         for (p = pkcs7->certs; p; p = p->next) {
 233                                 pr_debug("- cmp [%u] %*phN\n",
 234                                          p->index, p->id->len, p->id->data);
 235                                 if (asymmetric_key_id_same(p->id, auth))
 236                                         goto found_issuer_check_skid;
 237                         }
 238                 } else {
 239                         auth = x509->akid_skid;
 240                         pr_debug("- want %*phN\n", auth->len, auth->data);
 241                         for (p = pkcs7->certs; p; p = p->next) {
 242                                 if (!p->skid)
 243                                         continue;
 244                                 pr_debug("- cmp [%u] %*phN\n",
 245                                          p->index, p->skid->len, p->skid->data);
 246                                 if (asymmetric_key_id_same(p->skid, auth))
 247                                         goto found_issuer;
 248                         }
 249                 }
 250
 251                 /* We didn't find the root of this chain */
 252                 pr_debug("- top\n");
 253                 return 0;
 254
 255         found_issuer_check_skid:
 256                 /* We matched issuer + serialNumber, but if there's an
 257                  * authKeyId.keyId, that must match the CA subjKeyId also.
 258                  */
 259                 if (x509->akid_skid &&
 260                     !asymmetric_key_id_same(p->skid, x509->akid_skid)) {
 261                         pr_warn("Sig %u: X.509 chain contains auth-skid nonmatch (%u->%u)\n",
 262                                 sinfo->index, x509->index, p->index);
 263                         return -EKEYREJECTED;
 264                 }
 265         found_issuer:
 266                 pr_debug("- subject %s\n", p->subject);
 267                 if (p->seen) {
 268                         pr_warn("Sig %u: X.509 chain contains loop\n",
 269                                 sinfo->index);
 270                         return 0;
 271                 }
 272                 ret = x509_check_signature(p->pub, x509);
 273                 if (ret < 0)
 274                         return ret;
 275                 x509->signer = p;
 276                 if (x509 == p) {
 277                         pr_debug("- self-signed\n");
 278                         return 0;
 279                 }
 280                 x509 = p;
 281                 might_sleep();
 282         }
 283
 284 maybe_missing_crypto_in_x509:
 285         /* Just prune the certificate chain at this point if we lack some
 286          * crypto module to go further.  Note, however, we don't want to set
 287          * sinfo->missing_crypto as the signed info block may still be
 288          * validatable against an X.509 cert lower in the chain that we have a
 289          * trusted copy of.
 290          */
 291         if (ret == -ENOPKG)
 292                 return 0;
 293         return ret;
 294 }
 295
 296 /*
 297  * Verify one signed information block from a PKCS#7 message.
 298  */
 299 static int pkcs7_verify_one(struct pkcs7_message *pkcs7,
 300                             struct pkcs7_signed_info *sinfo)
 301 {
 302         int ret;
 303
 304         kenter(",%u", sinfo->index);
 305
 306         /* First of all, digest the data in the PKCS#7 message and the
 307          * signed information block
 308          */
 309         ret = pkcs7_digest(pkcs7, sinfo);
 310         if (ret < 0)
 311                 return ret;
 312
 313         /* Find the key for the signature if there is one */
 314         ret = pkcs7_find_key(pkcs7, sinfo);
 315         if (ret < 0)
 316                 return ret;
 317
 318         if (!sinfo->signer)
 319                 return 0;
 320
 321         pr_devel("Using X.509[%u] for sig %u\n",
 322                  sinfo->signer->index, sinfo->index);
 323
 324         /* Check that the PKCS#7 signing time is valid according to the X.509
 325          * certificate.  We can't, however, check against the system clock
 326          * since that may not have been set yet and may be wrong.
 327          */
 328         if (test_bit(sinfo_has_signing_time, &sinfo->aa_set)) {
 329                 if (sinfo->signing_time < sinfo->signer->valid_from ||
 330                     sinfo->signing_time > sinfo->signer->valid_to) {
 331                         pr_warn("Message signed outside of X.509 validity window\n");
 332                         return -EKEYREJECTED;
 333                 }
 334         }
 335
 336         /* Verify the PKCS#7 binary against the key */
 337         ret = public_key_verify_signature(sinfo->signer->pub, &sinfo->sig);
 338         if (ret < 0)
 339                 return ret;
 340
 341         pr_devel("Verified signature %u\n", sinfo->index);
 342
 343         /* Verify the internal certificate chain */
 344         return pkcs7_verify_sig_chain(pkcs7, sinfo);
 345 }
 346
 347 /**
 348  * pkcs7_verify - Verify a PKCS#7 message
 349  * @pkcs7: The PKCS#7 message to be verified
 350  * @usage: The use to which the key is being put
 351  *
 352  * Verify a PKCS#7 message is internally consistent - that is, the data digest
 353  * matches the digest in the AuthAttrs and any signature in the message or one
 354  * of the X.509 certificates it carries that matches another X.509 cert in the
 355  * message can be verified.
 356  *
 357  * This does not look to match the contents of the PKCS#7 message against any
 358  * external public keys.
 359  *
 360  * Returns, in order of descending priority:
 361  *
 362  *  (*) -EKEYREJECTED if a key was selected that had a usage restriction at
 363  *      odds with the specified usage, or:
 364  *
 365  *  (*) -EKEYREJECTED if a signature failed to match for which we found an
 366  *      appropriate X.509 certificate, or:
 367  *
 368  *  (*) -EBADMSG if some part of the message was invalid, or:
 369  *
 370  *  (*) -ENOPKG if none of the signature chains are verifiable because suitable
 371  *      crypto modules couldn't be found, or:
 372  *
 373  *  (*) 0 if all the signature chains that don't incur -ENOPKG can be verified
 374  *      (note that a signature chain may be of zero length), or:
 375  */
 376 int pkcs7_verify(struct pkcs7_message *pkcs7,
 377                  enum key_being_used_for usage)
 378 {
 379         struct pkcs7_signed_info *sinfo;
 380         struct x509_certificate *x509;
 381         int enopkg = -ENOPKG;
 382         int ret, n;
 383
 384         kenter("");
 385
 386         switch (usage) {
 387         case VERIFYING_MODULE_SIGNATURE:
 388                 if (pkcs7->data_type != OID_data) {
 389                         pr_warn("Invalid module sig (not pkcs7-data)\n");
 390                         return -EKEYREJECTED;
 391                 }
 392                 if (pkcs7->have_authattrs) {
 393                         pr_warn("Invalid module sig (has authattrs)\n");
 394                         return -EKEYREJECTED;
 395                 }
 396                 break;
 397         case VERIFYING_FIRMWARE_SIGNATURE:
 398                 if (pkcs7->data_type != OID_data) {
 399                         pr_warn("Invalid firmware sig (not pkcs7-data)\n");
 400                         return -EKEYREJECTED;
 401                 }
 402                 if (!pkcs7->have_authattrs) {
 403                         pr_warn("Invalid firmware sig (missing authattrs)\n");
 404                         return -EKEYREJECTED;
 405                 }
 406                 break;
 407         case VERIFYING_KEXEC_PE_SIGNATURE:
 408                 if (pkcs7->data_type != OID_msIndirectData) {
 409                         pr_warn("Invalid kexec sig (not Authenticode)\n");
 410                         return -EKEYREJECTED;
 411                 }
 412                 /* Authattr presence checked in parser */
 413                 break;
 414         case VERIFYING_UNSPECIFIED_SIGNATURE:
 415                 if (pkcs7->data_type != OID_data) {
 416                         pr_warn("Invalid unspecified sig (not pkcs7-data)\n");
 417                         return -EKEYREJECTED;
 418                 }
 419                 break;
 420         default:
 421                 return -EINVAL;
 422         }
 423
 424         for (n = 0, x509 = pkcs7->certs; x509; x509 = x509->next, n++) {
 425                 ret = x509_get_sig_params(x509);
 426                 if (ret < 0)
 427                         return ret;
 428         }
 429
 430         for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
 431                 ret = pkcs7_verify_one(pkcs7, sinfo);
 432                 if (ret < 0) {
 433                         if (ret == -ENOPKG) {
 434                                 sinfo->unsupported_crypto = true;
 435                                 continue;
 436                         }
 437                         kleave(" = %d", ret);
 438                         return ret;
 439                 }
 440                 enopkg = 0;
 441         }
 442
 443         kleave(" = %d", enopkg);
 444         return enopkg;
 445 }
 446 EXPORT_SYMBOL_GPL(pkcs7_verify);
 447
 448 /**
 449  * pkcs7_supply_detached_data - Supply the data needed to verify a PKCS#7 message
 450  * @pkcs7: The PKCS#7 message
 451  * @data: The data to be verified
 452  * @datalen: The amount of data
 453  *
 454  * Supply the detached data needed to verify a PKCS#7 message.  Note that no
 455  * attempt to retain/pin the data is made.  That is left to the caller.  The
 456  * data will not be modified by pkcs7_verify() and will not be freed when the
 457  * PKCS#7 message is freed.
 458  *
 459  * Returns -EINVAL if data is already supplied in the message, 0 otherwise.
 460  */
 461 int pkcs7_supply_detached_data(struct pkcs7_message *pkcs7,
 462                                const void *data, size_t datalen)
 463 {
 464         if (pkcs7->data) {
 465                 pr_debug("Data already supplied\n");
 466                 return -EINVAL;
 467         }
 468         pkcs7->data = data;
 469         pkcs7->data_len = datalen;
 470         return 0;
 471 }