crypto/asymmetric_keys/pkcs7_verify.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /* Verify the signature on a PKCS#7 message.
   3  *
   4  * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
   5  * Written by David Howells (dhowells@redhat.com)
   6  */
   7
   8 #define pr_fmt(fmt) "PKCS7: "fmt
   9 #include <linux/kernel.h>
  10 #include <linux/export.h>
  11 #include <linux/slab.h>
  12 #include <linux/err.h>
  13 #include <linux/asn1.h>
  14 #include <crypto/hash.h>
  15 #include <crypto/hash_info.h>
  16 #include <crypto/public_key.h>
  17 #include "pkcs7_parser.h"
  18
  19 /*
  20  * Digest the relevant parts of the PKCS#7 data
  21  */
  22 static int pkcs7_digest(struct pkcs7_message *pkcs7,
  23                         struct pkcs7_signed_info *sinfo)
  24 {
  25         struct public_key_signature *sig = sinfo->sig;
  26         struct crypto_shash *tfm;
  27         struct shash_desc *desc;
  28         size_t desc_size;
  29         int ret;
  30
  31         kenter(",%u,%s", sinfo->index, sinfo->sig->hash_algo);
  32
  33         /* The digest was calculated already. */
  34         if (sig->digest)
  35                 return 0;
  36
  37         if (!sinfo->sig->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(sinfo->sig->hash_algo, 0, 0);
  44         if (IS_ERR(tfm))
  45                 return (PTR_ERR(tfm) == -ENOENT) ? -ENOPKG : PTR_ERR(tfm);
  46
  47         desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
  48         sig->digest_size = crypto_shash_digestsize(tfm);
  49
  50         ret = -ENOMEM;
  51         sig->digest = kmalloc(sig->digest_size, GFP_KERNEL);
  52         if (!sig->digest)
  53                 goto error_no_desc;
  54
  55         desc = kzalloc(desc_size, GFP_KERNEL);
  56         if (!desc)
  57                 goto error_no_desc;
  58
  59         desc->tfm   = tfm;
  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 int pkcs7_get_digest(struct pkcs7_message *pkcs7, const u8 **buf, u32 *len,
 126                      enum hash_algo *hash_algo)
 127 {
 128         struct pkcs7_signed_info *sinfo = pkcs7->signed_infos;
 129         int i, ret;
 130
 131         /*
 132          * This function doesn't support messages with more than one signature.
 133          */
 134         if (sinfo == NULL || sinfo->next != NULL)
 135                 return -EBADMSG;
 136
 137         ret = pkcs7_digest(pkcs7, sinfo);
 138         if (ret)
 139                 return ret;
 140
 141         *buf = sinfo->sig->digest;
 142         *len = sinfo->sig->digest_size;
 143
 144         for (i = 0; i < HASH_ALGO__LAST; i++)
 145                 if (!strcmp(hash_algo_name[i], sinfo->sig->hash_algo)) {
 146                         *hash_algo = i;
 147                         break;
 148                 }
 149
 150         return 0;
 151 }
 152
 153 /*
 154  * Find the key (X.509 certificate) to use to verify a PKCS#7 message.  PKCS#7
 155  * uses the issuer's name and the issuing certificate serial number for
 156  * matching purposes.  These must match the certificate issuer's name (not
 157  * subject's name) and the certificate serial number [RFC 2315 6.7].
 158  */
 159 static int pkcs7_find_key(struct pkcs7_message *pkcs7,
 160                           struct pkcs7_signed_info *sinfo)
 161 {
 162         struct x509_certificate *x509;
 163         unsigned certix = 1;
 164
 165         kenter("%u", sinfo->index);
 166
 167         for (x509 = pkcs7->certs; x509; x509 = x509->next, certix++) {
 168                 /* I'm _assuming_ that the generator of the PKCS#7 message will
 169                  * encode the fields from the X.509 cert in the same way in the
 170                  * PKCS#7 message - but I can't be 100% sure of that.  It's
 171                  * possible this will need element-by-element comparison.
 172                  */
 173                 if (!asymmetric_key_id_same(x509->id, sinfo->sig->auth_ids[0]))
 174                         continue;
 175                 pr_devel("Sig %u: Found cert serial match X.509[%u]\n",
 176                          sinfo->index, certix);
 177
 178                 if (strcmp(x509->pub->pkey_algo, sinfo->sig->pkey_algo) != 0) {
 179                         pr_warn("Sig %u: X.509 algo and PKCS#7 sig algo don't match\n",
 180                                 sinfo->index);
 181                         continue;
 182                 }
 183
 184                 sinfo->signer = x509;
 185                 return 0;
 186         }
 187
 188         /* The relevant X.509 cert isn't found here, but it might be found in
 189          * the trust keyring.
 190          */
 191         pr_debug("Sig %u: Issuing X.509 cert not found (#%*phN)\n",
 192                  sinfo->index,
 193                  sinfo->sig->auth_ids[0]->len, sinfo->sig->auth_ids[0]->data);
 194         return 0;
 195 }
 196
 197 /*
 198  * Verify the internal certificate chain as best we can.
 199  */
 200 static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7,
 201                                   struct pkcs7_signed_info *sinfo)
 202 {
 203         struct public_key_signature *sig;
 204         struct x509_certificate *x509 = sinfo->signer, *p;
 205         struct asymmetric_key_id *auth;
 206         int ret;
 207
 208         kenter("");
 209
 210         for (p = pkcs7->certs; p; p = p->next)
 211                 p->seen = false;
 212
 213         for (;;) {
 214                 pr_debug("verify %s: %*phN\n",
 215                          x509->subject,
 216                          x509->raw_serial_size, x509->raw_serial);
 217                 x509->seen = true;
 218
 219                 if (x509->blacklisted) {
 220                         /* If this cert is blacklisted, then mark everything
 221                          * that depends on this as blacklisted too.
 222                          */
 223                         sinfo->blacklisted = true;
 224                         for (p = sinfo->signer; p != x509; p = p->signer)
 225                                 p->blacklisted = true;
 226                         pr_debug("- blacklisted\n");
 227                         return 0;
 228                 }
 229
 230                 if (x509->unsupported_key)
 231                         goto unsupported_crypto_in_x509;
 232
 233                 pr_debug("- issuer %s\n", x509->issuer);
 234                 sig = x509->sig;
 235                 if (sig->auth_ids[0])
 236                         pr_debug("- authkeyid.id %*phN\n",
 237                                  sig->auth_ids[0]->len, sig->auth_ids[0]->data);
 238                 if (sig->auth_ids[1])
 239                         pr_debug("- authkeyid.skid %*phN\n",
 240                                  sig->auth_ids[1]->len, sig->auth_ids[1]->data);
 241
 242                 if (x509->self_signed) {
 243                         /* If there's no authority certificate specified, then
 244                          * the certificate must be self-signed and is the root
 245                          * of the chain.  Likewise if the cert is its own
 246                          * authority.
 247                          */
 248                         if (x509->unsupported_sig)
 249                                 goto unsupported_crypto_in_x509;
 250                         x509->signer = x509;
 251                         pr_debug("- self-signed\n");
 252                         return 0;
 253                 }
 254
 255                 /* Look through the X.509 certificates in the PKCS#7 message's
 256                  * list to see if the next one is there.
 257                  */
 258                 auth = sig->auth_ids[0];
 259                 if (auth) {
 260                         pr_debug("- want %*phN\n", auth->len, auth->data);
 261                         for (p = pkcs7->certs; p; p = p->next) {
 262                                 pr_debug("- cmp [%u] %*phN\n",
 263                                          p->index, p->id->len, p->id->data);
 264                                 if (asymmetric_key_id_same(p->id, auth))
 265                                         goto found_issuer_check_skid;
 266                         }
 267                 } else if (sig->auth_ids[1]) {
 268                         auth = sig->auth_ids[1];
 269                         pr_debug("- want %*phN\n", auth->len, auth->data);
 270                         for (p = pkcs7->certs; p; p = p->next) {
 271                                 if (!p->skid)
 272                                         continue;
 273                                 pr_debug("- cmp [%u] %*phN\n",
 274                                          p->index, p->skid->len, p->skid->data);
 275                                 if (asymmetric_key_id_same(p->skid, auth))
 276                                         goto found_issuer;
 277                         }
 278                 }
 279
 280                 /* We didn't find the root of this chain */
 281                 pr_debug("- top\n");
 282                 return 0;
 283
 284         found_issuer_check_skid:
 285                 /* We matched issuer + serialNumber, but if there's an
 286                  * authKeyId.keyId, that must match the CA subjKeyId also.
 287                  */
 288                 if (sig->auth_ids[1] &&
 289                     !asymmetric_key_id_same(p->skid, sig->auth_ids[1])) {
 290                         pr_warn("Sig %u: X.509 chain contains auth-skid nonmatch (%u->%u)\n",
 291                                 sinfo->index, x509->index, p->index);
 292                         return -EKEYREJECTED;
 293                 }
 294         found_issuer:
 295                 pr_debug("- subject %s\n", p->subject);
 296                 if (p->seen) {
 297                         pr_warn("Sig %u: X.509 chain contains loop\n",
 298                                 sinfo->index);
 299                         return 0;
 300                 }
 301                 ret = public_key_verify_signature(p->pub, x509->sig);
 302                 if (ret < 0)
 303                         return ret;
 304                 x509->signer = p;
 305                 if (x509 == p) {
 306                         pr_debug("- self-signed\n");
 307                         return 0;
 308                 }
 309                 x509 = p;
 310                 might_sleep();
 311         }
 312
 313 unsupported_crypto_in_x509:
 314         /* Just prune the certificate chain at this point if we lack some
 315          * crypto module to go further.  Note, however, we don't want to set
 316          * sinfo->unsupported_crypto as the signed info block may still be
 317          * validatable against an X.509 cert lower in the chain that we have a
 318          * trusted copy of.
 319          */
 320         return 0;
 321 }
 322
 323 /*
 324  * Verify one signed information block from a PKCS#7 message.
 325  */
 326 static int pkcs7_verify_one(struct pkcs7_message *pkcs7,
 327                             struct pkcs7_signed_info *sinfo)
 328 {
 329         int ret;
 330
 331         kenter(",%u", sinfo->index);
 332
 333         /* First of all, digest the data in the PKCS#7 message and the
 334          * signed information block
 335          */
 336         ret = pkcs7_digest(pkcs7, sinfo);
 337         if (ret < 0)
 338                 return ret;
 339
 340         /* Find the key for the signature if there is one */
 341         ret = pkcs7_find_key(pkcs7, sinfo);
 342         if (ret < 0)
 343                 return ret;
 344
 345         if (!sinfo->signer)
 346                 return 0;
 347
 348         pr_devel("Using X.509[%u] for sig %u\n",
 349                  sinfo->signer->index, sinfo->index);
 350
 351         /* Check that the PKCS#7 signing time is valid according to the X.509
 352          * certificate.  We can't, however, check against the system clock
 353          * since that may not have been set yet and may be wrong.
 354          */
 355         if (test_bit(sinfo_has_signing_time, &sinfo->aa_set)) {
 356                 if (sinfo->signing_time < sinfo->signer->valid_from ||
 357                     sinfo->signing_time > sinfo->signer->valid_to) {
 358                         pr_warn("Message signed outside of X.509 validity window\n");
 359                         return -EKEYREJECTED;
 360                 }
 361         }
 362
 363         /* Verify the PKCS#7 binary against the key */
 364         ret = public_key_verify_signature(sinfo->signer->pub, sinfo->sig);
 365         if (ret < 0)
 366                 return ret;
 367
 368         pr_devel("Verified signature %u\n", sinfo->index);
 369
 370         /* Verify the internal certificate chain */
 371         return pkcs7_verify_sig_chain(pkcs7, sinfo);
 372 }
 373
 374 /**
 375  * pkcs7_verify - Verify a PKCS#7 message
 376  * @pkcs7: The PKCS#7 message to be verified
 377  * @usage: The use to which the key is being put
 378  *
 379  * Verify a PKCS#7 message is internally consistent - that is, the data digest
 380  * matches the digest in the AuthAttrs and any signature in the message or one
 381  * of the X.509 certificates it carries that matches another X.509 cert in the
 382  * message can be verified.
 383  *
 384  * This does not look to match the contents of the PKCS#7 message against any
 385  * external public keys.
 386  *
 387  * Returns, in order of descending priority:
 388  *
 389  *  (*) -EKEYREJECTED if a key was selected that had a usage restriction at
 390  *      odds with the specified usage, or:
 391  *
 392  *  (*) -EKEYREJECTED if a signature failed to match for which we found an
 393  *      appropriate X.509 certificate, or:
 394  *
 395  *  (*) -EBADMSG if some part of the message was invalid, or:
 396  *
 397  *  (*) 0 if a signature chain passed verification, or:
 398  *
 399  *  (*) -EKEYREJECTED if a blacklisted key was encountered, or:
 400  *
 401  *  (*) -ENOPKG if none of the signature chains are verifiable because suitable
 402  *      crypto modules couldn't be found.
 403  */
 404 int pkcs7_verify(struct pkcs7_message *pkcs7,
 405                  enum key_being_used_for usage)
 406 {
 407         struct pkcs7_signed_info *sinfo;
 408         int actual_ret = -ENOPKG;
 409         int ret;
 410
 411         kenter("");
 412
 413         switch (usage) {
 414         case VERIFYING_MODULE_SIGNATURE:
 415                 if (pkcs7->data_type != OID_data) {
 416                         pr_warn("Invalid module sig (not pkcs7-data)\n");
 417                         return -EKEYREJECTED;
 418                 }
 419                 if (pkcs7->have_authattrs) {
 420                         pr_warn("Invalid module sig (has authattrs)\n");
 421                         return -EKEYREJECTED;
 422                 }
 423                 break;
 424         case VERIFYING_FIRMWARE_SIGNATURE:
 425                 if (pkcs7->data_type != OID_data) {
 426                         pr_warn("Invalid firmware sig (not pkcs7-data)\n");
 427                         return -EKEYREJECTED;
 428                 }
 429                 if (!pkcs7->have_authattrs) {
 430                         pr_warn("Invalid firmware sig (missing authattrs)\n");
 431                         return -EKEYREJECTED;
 432                 }
 433                 break;
 434         case VERIFYING_KEXEC_PE_SIGNATURE:
 435                 if (pkcs7->data_type != OID_msIndirectData) {
 436                         pr_warn("Invalid kexec sig (not Authenticode)\n");
 437                         return -EKEYREJECTED;
 438                 }
 439                 /* Authattr presence checked in parser */
 440                 break;
 441         case VERIFYING_UNSPECIFIED_SIGNATURE:
 442                 if (pkcs7->data_type != OID_data) {
 443                         pr_warn("Invalid unspecified sig (not pkcs7-data)\n");
 444                         return -EKEYREJECTED;
 445                 }
 446                 break;
 447         default:
 448                 return -EINVAL;
 449         }
 450
 451         for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
 452                 ret = pkcs7_verify_one(pkcs7, sinfo);
 453                 if (sinfo->blacklisted) {
 454                         if (actual_ret == -ENOPKG)
 455                                 actual_ret = -EKEYREJECTED;
 456                         continue;
 457                 }
 458                 if (ret < 0) {
 459                         if (ret == -ENOPKG) {
 460                                 sinfo->unsupported_crypto = true;
 461                                 continue;
 462                         }
 463                         kleave(" = %d", ret);
 464                         return ret;
 465                 }
 466                 actual_ret = 0;
 467         }
 468
 469         kleave(" = %d", actual_ret);
 470         return actual_ret;
 471 }
 472 EXPORT_SYMBOL_GPL(pkcs7_verify);
 473
 474 /**
 475  * pkcs7_supply_detached_data - Supply the data needed to verify a PKCS#7 message
 476  * @pkcs7: The PKCS#7 message
 477  * @data: The data to be verified
 478  * @datalen: The amount of data
 479  *
 480  * Supply the detached data needed to verify a PKCS#7 message.  Note that no
 481  * attempt to retain/pin the data is made.  That is left to the caller.  The
 482  * data will not be modified by pkcs7_verify() and will not be freed when the
 483  * PKCS#7 message is freed.
 484  *
 485  * Returns -EINVAL if data is already supplied in the message, 0 otherwise.
 486  */
 487 int pkcs7_supply_detached_data(struct pkcs7_message *pkcs7,
 488                                const void *data, size_t datalen)
 489 {
 490         if (pkcs7->data) {
 491                 pr_debug("Data already supplied\n");
 492                 return -EINVAL;
 493         }
 494         pkcs7->data = data;
 495         pkcs7->data_len = datalen;
 496         return 0;
 497 }