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