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 <crypto/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 public_key_signature *sig = sinfo->sig;
  29         struct crypto_shash *tfm;
  30         struct shash_desc *desc;
  31         size_t desc_size;
  32         int ret;
  33
  34         kenter(",%u,%s", sinfo->index, sinfo->sig->hash_algo);
  35
  36         if (!sinfo->sig->hash_algo)
  37                 return -ENOPKG;
  38
  39         /* Allocate the hashing algorithm we're going to need and find out how
  40          * big the hash operational data will be.
  41          */
  42         tfm = crypto_alloc_shash(sinfo->sig->hash_algo, 0, 0);
  43         if (IS_ERR(tfm))
  44                 return (PTR_ERR(tfm) == -ENOENT) ? -ENOPKG : PTR_ERR(tfm);
  45
  46         desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
  47         sig->digest_size = crypto_shash_digestsize(tfm);
  48
  49         ret = -ENOMEM;
  50         sig->digest = kmalloc(sig->digest_size, GFP_KERNEL);
  51         if (!sig->digest)
  52                 goto error_no_desc;
  53
  54         desc = kzalloc(desc_size, GFP_KERNEL);
  55         if (!desc)
  56                 goto error_no_desc;
  57
  58         desc->tfm   = tfm;
  59         desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
  60
  61         /* Digest the message [RFC2315 9.3] */
  62         ret = crypto_shash_digest(desc, pkcs7->data, pkcs7->data_len,
  63                                   sig->digest);
  64         if (ret < 0)
  65                 goto error;
  66         pr_devel("MsgDigest = [%*ph]\n", 8, sig->digest);
  67
  68         /* However, if there are authenticated attributes, there must be a
  69          * message digest attribute amongst them which corresponds to the
  70          * digest we just calculated.
  71          */
  72         if (sinfo->authattrs) {
  73                 u8 tag;
  74
  75                 if (!sinfo->msgdigest) {
  76                         pr_warn("Sig %u: No messageDigest\n", sinfo->index);
  77                         ret = -EKEYREJECTED;
  78                         goto error;
  79                 }
  80
  81                 if (sinfo->msgdigest_len != sig->digest_size) {
  82                         pr_debug("Sig %u: Invalid digest size (%u)\n",
  83                                  sinfo->index, sinfo->msgdigest_len);
  84                         ret = -EBADMSG;
  85                         goto error;
  86                 }
  87
  88                 if (memcmp(sig->digest, sinfo->msgdigest,
  89                            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(sig->digest, 0, 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, sig->digest);
 112                 if (ret < 0)
 113                         goto error;
 114                 pr_devel("AADigest = [%*ph]\n", 8, sig->digest);
 115         }
 116
 117 error:
 118         kfree(desc);
 119 error_no_desc:
 120         crypto_free_shash(tfm);
 121         kleave(" = %d", ret);
 122         return ret;
 123 }
 124
 125 /*
 126  * Find the key (X.509 certificate) to use to verify a PKCS#7 message.  PKCS#7
 127  * uses the issuer's name and the issuing certificate serial number for
 128  * matching purposes.  These must match the certificate issuer's name (not
 129  * subject's name) and the certificate serial number [RFC 2315 6.7].
 130  */
 131 static int pkcs7_find_key(struct pkcs7_message *pkcs7,
 132                           struct pkcs7_signed_info *sinfo)
 133 {
 134         struct x509_certificate *x509;
 135         unsigned certix = 1;
 136
 137         kenter("%u", sinfo->index);
 138
 139         for (x509 = pkcs7->certs; x509; x509 = x509->next, certix++) {
 140                 /* I'm _assuming_ that the generator of the PKCS#7 message will
 141                  * encode the fields from the X.509 cert in the same way in the
 142                  * PKCS#7 message - but I can't be 100% sure of that.  It's
 143                  * possible this will need element-by-element comparison.
 144                  */
 145                 if (!asymmetric_key_id_same(x509->id, sinfo->sig->auth_ids[0]))
 146                         continue;
 147                 pr_devel("Sig %u: Found cert serial match X.509[%u]\n",
 148                          sinfo->index, certix);
 149
 150                 if (strcmp(x509->pub->pkey_algo, sinfo->sig->pkey_algo) != 0) {
 151                         pr_warn("Sig %u: X.509 algo and PKCS#7 sig algo don't match\n",
 152                                 sinfo->index);
 153                         continue;
 154                 }
 155
 156                 sinfo->signer = x509;
 157                 return 0;
 158         }
 159
 160         /* The relevant X.509 cert isn't found here, but it might be found in
 161          * the trust keyring.
 162          */
 163         pr_debug("Sig %u: Issuing X.509 cert not found (#%*phN)\n",
 164                  sinfo->index,
 165                  sinfo->sig->auth_ids[0]->len, sinfo->sig->auth_ids[0]->data);
 166         return 0;
 167 }
 168
 169 /*
 170  * Verify the internal certificate chain as best we can.
 171  */
 172 static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7,
 173                                   struct pkcs7_signed_info *sinfo)
 174 {
 175         struct public_key_signature *sig;
 176         struct x509_certificate *x509 = sinfo->signer, *p;
 177         struct asymmetric_key_id *auth;
 178         int ret;
 179
 180         kenter("");
 181
 182         for (p = pkcs7->certs; p; p = p->next)
 183                 p->seen = false;
 184
 185         for (;;) {
 186                 pr_debug("verify %s: %*phN\n",
 187                          x509->subject,
 188                          x509->raw_serial_size, x509->raw_serial);
 189                 x509->seen = true;
 190
 191                 if (x509->blacklisted) {
 192                         /* If this cert is blacklisted, then mark everything
 193                          * that depends on this as blacklisted too.
 194                          */
 195                         sinfo->blacklisted = true;
 196                         for (p = sinfo->signer; p != x509; p = p->signer)
 197                                 p->blacklisted = true;
 198                         pr_debug("- blacklisted\n");
 199                         return 0;
 200                 }
 201
 202                 if (x509->unsupported_key)
 203                         goto unsupported_crypto_in_x509;
 204
 205                 pr_debug("- issuer %s\n", x509->issuer);
 206                 sig = x509->sig;
 207                 if (sig->auth_ids[0])
 208                         pr_debug("- authkeyid.id %*phN\n",
 209                                  sig->auth_ids[0]->len, sig->auth_ids[0]->data);
 210                 if (sig->auth_ids[1])
 211                         pr_debug("- authkeyid.skid %*phN\n",
 212                                  sig->auth_ids[1]->len, sig->auth_ids[1]->data);
 213
 214                 if (x509->self_signed) {
 215                         /* If there's no authority certificate specified, then
 216                          * the certificate must be self-signed and is the root
 217                          * of the chain.  Likewise if the cert is its own
 218                          * authority.
 219                          */
 220                         if (x509->unsupported_sig)
 221                                 goto unsupported_crypto_in_x509;
 222                         x509->signer = x509;
 223                         pr_debug("- self-signed\n");
 224                         return 0;
 225                 }
 226
 227                 /* Look through the X.509 certificates in the PKCS#7 message's
 228                  * list to see if the next one is there.
 229                  */
 230                 auth = sig->auth_ids[0];
 231                 if (auth) {
 232                         pr_debug("- want %*phN\n", auth->len, auth->data);
 233                         for (p = pkcs7->certs; p; p = p->next) {
 234                                 pr_debug("- cmp [%u] %*phN\n",
 235                                          p->index, p->id->len, p->id->data);
 236                                 if (asymmetric_key_id_same(p->id, auth))
 237                                         goto found_issuer_check_skid;
 238                         }
 239                 } else if (sig->auth_ids[1]) {
 240                         auth = sig->auth_ids[1];
 241                         pr_debug("- want %*phN\n", auth->len, auth->data);
 242                         for (p = pkcs7->certs; p; p = p->next) {
 243                                 if (!p->skid)
 244                                         continue;
 245                                 pr_debug("- cmp [%u] %*phN\n",
 246                                          p->index, p->skid->len, p->skid->data);
 247                                 if (asymmetric_key_id_same(p->skid, auth))
 248                                         goto found_issuer;
 249                         }
 250                 }
 251
 252                 /* We didn't find the root of this chain */
 253                 pr_debug("- top\n");
 254                 return 0;
 255
 256         found_issuer_check_skid:
 257                 /* We matched issuer + serialNumber, but if there's an
 258                  * authKeyId.keyId, that must match the CA subjKeyId also.
 259                  */
 260                 if (sig->auth_ids[1] &&
 261                     !asymmetric_key_id_same(p->skid, sig->auth_ids[1])) {
 262                         pr_warn("Sig %u: X.509 chain contains auth-skid nonmatch (%u->%u)\n",
 263                                 sinfo->index, x509->index, p->index);
 264                         return -EKEYREJECTED;
 265                 }
 266         found_issuer:
 267                 pr_debug("- subject %s\n", p->subject);
 268                 if (p->seen) {
 269                         pr_warn("Sig %u: X.509 chain contains loop\n",
 270                                 sinfo->index);
 271                         return 0;
 272                 }
 273                 ret = public_key_verify_signature(p->pub, p->sig);
 274                 if (ret < 0)
 275                         return ret;
 276                 x509->signer = p;
 277                 if (x509 == p) {
 278                         pr_debug("- self-signed\n");
 279                         return 0;
 280                 }
 281                 x509 = p;
 282                 might_sleep();
 283         }
 284
 285 unsupported_crypto_in_x509:
 286         /* Just prune the certificate chain at this point if we lack some
 287          * crypto module to go further.  Note, however, we don't want to set
 288          * sinfo->unsupported_crypto as the signed info block may still be
 289          * validatable against an X.509 cert lower in the chain that we have a
 290          * trusted copy of.
 291          */
 292         return 0;
 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  *  (*) 0 if no signature chains were found to be blacklisted or to contain
 370  *      unsupported crypto, or:
 371  *
 372  *  (*) -EKEYREJECTED if a blacklisted key was encountered, or:
 373  *
 374  *  (*) -ENOPKG if none of the signature chains are verifiable because suitable
 375  *      crypto modules couldn't be found.
 376  */
 377 int pkcs7_verify(struct pkcs7_message *pkcs7,
 378                  enum key_being_used_for usage)
 379 {
 380         struct pkcs7_signed_info *sinfo;
 381         int actual_ret = -ENOPKG;
 382         int ret;
 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 (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
 425                 ret = pkcs7_verify_one(pkcs7, sinfo);
 426                 if (sinfo->blacklisted && actual_ret == -ENOPKG)
 427                         actual_ret = -EKEYREJECTED;
 428                 if (ret < 0) {
 429                         if (ret == -ENOPKG) {
 430                                 sinfo->unsupported_crypto = true;
 431                                 continue;
 432                         }
 433                         kleave(" = %d", ret);
 434                         return ret;
 435                 }
 436                 actual_ret = 0;
 437         }
 438
 439         kleave(" = %d", actual_ret);
 440         return actual_ret;
 441 }
 442 EXPORT_SYMBOL_GPL(pkcs7_verify);
 443
 444 /**
 445  * pkcs7_supply_detached_data - Supply the data needed to verify a PKCS#7 message
 446  * @pkcs7: The PKCS#7 message
 447  * @data: The data to be verified
 448  * @datalen: The amount of data
 449  *
 450  * Supply the detached data needed to verify a PKCS#7 message.  Note that no
 451  * attempt to retain/pin the data is made.  That is left to the caller.  The
 452  * data will not be modified by pkcs7_verify() and will not be freed when the
 453  * PKCS#7 message is freed.
 454  *
 455  * Returns -EINVAL if data is already supplied in the message, 0 otherwise.
 456  */
 457 int pkcs7_supply_detached_data(struct pkcs7_message *pkcs7,
 458                                const void *data, size_t datalen)
 459 {
 460         if (pkcs7->data) {
 461                 pr_debug("Data already supplied\n");
 462                 return -EINVAL;
 463         }
 464         pkcs7->data = data;
 465         pkcs7->data_len = datalen;
 466         return 0;
 467 }