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_warn("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_warn("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         i = match_string(hash_algo_name, HASH_ALGO__LAST,
 145                          sinfo->sig->hash_algo);
 146         if (i >= 0)
 147                 *hash_algo = i;
 148
 149         return 0;
 150 }
 151
 152 /*
 153  * Find the key (X.509 certificate) to use to verify a PKCS#7 message.  PKCS#7
 154  * uses the issuer's name and the issuing certificate serial number for
 155  * matching purposes.  These must match the certificate issuer's name (not
 156  * subject's name) and the certificate serial number [RFC 2315 6.7].
 157  */
 158 static int pkcs7_find_key(struct pkcs7_message *pkcs7,
 159                           struct pkcs7_signed_info *sinfo)
 160 {
 161         struct x509_certificate *x509;
 162         unsigned certix = 1;
 163
 164         kenter("%u", sinfo->index);
 165
 166         for (x509 = pkcs7->certs; x509; x509 = x509->next, certix++) {
 167                 /* I'm _assuming_ that the generator of the PKCS#7 message will
 168                  * encode the fields from the X.509 cert in the same way in the
 169                  * PKCS#7 message - but I can't be 100% sure of that.  It's
 170                  * possible this will need element-by-element comparison.
 171                  */
 172                 if (!asymmetric_key_id_same(x509->id, sinfo->sig->auth_ids[0]))
 173                         continue;
 174                 pr_devel("Sig %u: Found cert serial match X.509[%u]\n",
 175                          sinfo->index, certix);
 176
 177                 sinfo->signer = x509;
 178                 return 0;
 179         }
 180
 181         /* The relevant X.509 cert isn't found here, but it might be found in
 182          * the trust keyring.
 183          */
 184         pr_debug("Sig %u: Issuing X.509 cert not found (#%*phN)\n",
 185                  sinfo->index,
 186                  sinfo->sig->auth_ids[0]->len, sinfo->sig->auth_ids[0]->data);
 187         return 0;
 188 }
 189
 190 /*
 191  * Verify the internal certificate chain as best we can.
 192  */
 193 static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7,
 194                                   struct pkcs7_signed_info *sinfo)
 195 {
 196         struct public_key_signature *sig;
 197         struct x509_certificate *x509 = sinfo->signer, *p;
 198         struct asymmetric_key_id *auth;
 199         int ret;
 200
 201         kenter("");
 202
 203         for (p = pkcs7->certs; p; p = p->next)
 204                 p->seen = false;
 205
 206         for (;;) {
 207                 pr_debug("verify %s: %*phN\n",
 208                          x509->subject,
 209                          x509->raw_serial_size, x509->raw_serial);
 210                 x509->seen = true;
 211
 212                 if (x509->blacklisted) {
 213                         /* If this cert is blacklisted, then mark everything
 214                          * that depends on this as blacklisted too.
 215                          */
 216                         sinfo->blacklisted = true;
 217                         for (p = sinfo->signer; p != x509; p = p->signer)
 218                                 p->blacklisted = true;
 219                         pr_debug("- blacklisted\n");
 220                         return 0;
 221                 }
 222
 223                 pr_debug("- issuer %s\n", x509->issuer);
 224                 sig = x509->sig;
 225                 if (sig->auth_ids[0])
 226                         pr_debug("- authkeyid.id %*phN\n",
 227                                  sig->auth_ids[0]->len, sig->auth_ids[0]->data);
 228                 if (sig->auth_ids[1])
 229                         pr_debug("- authkeyid.skid %*phN\n",
 230                                  sig->auth_ids[1]->len, sig->auth_ids[1]->data);
 231
 232                 if (x509->self_signed) {
 233                         /* If there's no authority certificate specified, then
 234                          * the certificate must be self-signed and is the root
 235                          * of the chain.  Likewise if the cert is its own
 236                          * authority.
 237                          */
 238                         if (x509->unsupported_sig)
 239                                 goto unsupported_sig_in_x509;
 240                         x509->signer = x509;
 241                         pr_debug("- self-signed\n");
 242                         return 0;
 243                 }
 244
 245                 /* Look through the X.509 certificates in the PKCS#7 message's
 246                  * list to see if the next one is there.
 247                  */
 248                 auth = sig->auth_ids[0];
 249                 if (auth) {
 250                         pr_debug("- want %*phN\n", auth->len, auth->data);
 251                         for (p = pkcs7->certs; p; p = p->next) {
 252                                 pr_debug("- cmp [%u] %*phN\n",
 253                                          p->index, p->id->len, p->id->data);
 254                                 if (asymmetric_key_id_same(p->id, auth))
 255                                         goto found_issuer_check_skid;
 256                         }
 257                 } else if (sig->auth_ids[1]) {
 258                         auth = sig->auth_ids[1];
 259                         pr_debug("- want %*phN\n", auth->len, auth->data);
 260                         for (p = pkcs7->certs; p; p = p->next) {
 261                                 if (!p->skid)
 262                                         continue;
 263                                 pr_debug("- cmp [%u] %*phN\n",
 264                                          p->index, p->skid->len, p->skid->data);
 265                                 if (asymmetric_key_id_same(p->skid, auth))
 266                                         goto found_issuer;
 267                         }
 268                 }
 269
 270                 /* We didn't find the root of this chain */
 271                 pr_debug("- top\n");
 272                 return 0;
 273
 274         found_issuer_check_skid:
 275                 /* We matched issuer + serialNumber, but if there's an
 276                  * authKeyId.keyId, that must match the CA subjKeyId also.
 277                  */
 278                 if (sig->auth_ids[1] &&
 279                     !asymmetric_key_id_same(p->skid, sig->auth_ids[1])) {
 280                         pr_warn("Sig %u: X.509 chain contains auth-skid nonmatch (%u->%u)\n",
 281                                 sinfo->index, x509->index, p->index);
 282                         return -EKEYREJECTED;
 283                 }
 284         found_issuer:
 285                 pr_debug("- subject %s\n", p->subject);
 286                 if (p->seen) {
 287                         pr_warn("Sig %u: X.509 chain contains loop\n",
 288                                 sinfo->index);
 289                         return 0;
 290                 }
 291                 ret = public_key_verify_signature(p->pub, x509->sig);
 292                 if (ret < 0)
 293                         return ret;
 294                 x509->signer = p;
 295                 if (x509 == p) {
 296                         pr_debug("- self-signed\n");
 297                         return 0;
 298                 }
 299                 x509 = p;
 300                 might_sleep();
 301         }
 302
 303 unsupported_sig_in_x509:
 304         /* Just prune the certificate chain at this point if we lack some
 305          * crypto module to go further.  Note, however, we don't want to set
 306          * sinfo->unsupported_crypto as the signed info block may still be
 307          * validatable against an X.509 cert lower in the chain that we have a
 308          * trusted copy of.
 309          */
 310         return 0;
 311 }
 312
 313 /*
 314  * Verify one signed information block from a PKCS#7 message.
 315  */
 316 static int pkcs7_verify_one(struct pkcs7_message *pkcs7,
 317                             struct pkcs7_signed_info *sinfo)
 318 {
 319         int ret;
 320
 321         kenter(",%u", sinfo->index);
 322
 323         /* First of all, digest the data in the PKCS#7 message and the
 324          * signed information block
 325          */
 326         ret = pkcs7_digest(pkcs7, sinfo);
 327         if (ret < 0)
 328                 return ret;
 329
 330         /* Find the key for the signature if there is one */
 331         ret = pkcs7_find_key(pkcs7, sinfo);
 332         if (ret < 0)
 333                 return ret;
 334
 335         if (!sinfo->signer)
 336                 return 0;
 337
 338         pr_devel("Using X.509[%u] for sig %u\n",
 339                  sinfo->signer->index, sinfo->index);
 340
 341         /* Check that the PKCS#7 signing time is valid according to the X.509
 342          * certificate.  We can't, however, check against the system clock
 343          * since that may not have been set yet and may be wrong.
 344          */
 345         if (test_bit(sinfo_has_signing_time, &sinfo->aa_set)) {
 346                 if (sinfo->signing_time < sinfo->signer->valid_from ||
 347                     sinfo->signing_time > sinfo->signer->valid_to) {
 348                         pr_warn("Message signed outside of X.509 validity window\n");
 349                         return -EKEYREJECTED;
 350                 }
 351         }
 352
 353         /* Verify the PKCS#7 binary against the key */
 354         ret = public_key_verify_signature(sinfo->signer->pub, sinfo->sig);
 355         if (ret < 0)
 356                 return ret;
 357
 358         pr_devel("Verified signature %u\n", sinfo->index);
 359
 360         /* Verify the internal certificate chain */
 361         return pkcs7_verify_sig_chain(pkcs7, sinfo);
 362 }
 363
 364 /**
 365  * pkcs7_verify - Verify a PKCS#7 message
 366  * @pkcs7: The PKCS#7 message to be verified
 367  * @usage: The use to which the key is being put
 368  *
 369  * Verify a PKCS#7 message is internally consistent - that is, the data digest
 370  * matches the digest in the AuthAttrs and any signature in the message or one
 371  * of the X.509 certificates it carries that matches another X.509 cert in the
 372  * message can be verified.
 373  *
 374  * This does not look to match the contents of the PKCS#7 message against any
 375  * external public keys.
 376  *
 377  * Returns, in order of descending priority:
 378  *
 379  *  (*) -EKEYREJECTED if a key was selected that had a usage restriction at
 380  *      odds with the specified usage, or:
 381  *
 382  *  (*) -EKEYREJECTED if a signature failed to match for which we found an
 383  *      appropriate X.509 certificate, or:
 384  *
 385  *  (*) -EBADMSG if some part of the message was invalid, or:
 386  *
 387  *  (*) 0 if a signature chain passed verification, or:
 388  *
 389  *  (*) -EKEYREJECTED if a blacklisted key was encountered, or:
 390  *
 391  *  (*) -ENOPKG if none of the signature chains are verifiable because suitable
 392  *      crypto modules couldn't be found.
 393  */
 394 int pkcs7_verify(struct pkcs7_message *pkcs7,
 395                  enum key_being_used_for usage)
 396 {
 397         struct pkcs7_signed_info *sinfo;
 398         int actual_ret = -ENOPKG;
 399         int ret;
 400
 401         kenter("");
 402
 403         switch (usage) {
 404         case VERIFYING_MODULE_SIGNATURE:
 405                 if (pkcs7->data_type != OID_data) {
 406                         pr_warn("Invalid module sig (not pkcs7-data)\n");
 407                         return -EKEYREJECTED;
 408                 }
 409                 if (pkcs7->have_authattrs) {
 410                         pr_warn("Invalid module sig (has authattrs)\n");
 411                         return -EKEYREJECTED;
 412                 }
 413                 break;
 414         case VERIFYING_FIRMWARE_SIGNATURE:
 415                 if (pkcs7->data_type != OID_data) {
 416                         pr_warn("Invalid firmware sig (not pkcs7-data)\n");
 417                         return -EKEYREJECTED;
 418                 }
 419                 if (!pkcs7->have_authattrs) {
 420                         pr_warn("Invalid firmware sig (missing authattrs)\n");
 421                         return -EKEYREJECTED;
 422                 }
 423                 break;
 424         case VERIFYING_KEXEC_PE_SIGNATURE:
 425                 if (pkcs7->data_type != OID_msIndirectData) {
 426                         pr_warn("Invalid kexec sig (not Authenticode)\n");
 427                         return -EKEYREJECTED;
 428                 }
 429                 /* Authattr presence checked in parser */
 430                 break;
 431         case VERIFYING_UNSPECIFIED_SIGNATURE:
 432                 if (pkcs7->data_type != OID_data) {
 433                         pr_warn("Invalid unspecified sig (not pkcs7-data)\n");
 434                         return -EKEYREJECTED;
 435                 }
 436                 break;
 437         default:
 438                 return -EINVAL;
 439         }
 440
 441         for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
 442                 ret = pkcs7_verify_one(pkcs7, sinfo);
 443                 if (sinfo->blacklisted) {
 444                         if (actual_ret == -ENOPKG)
 445                                 actual_ret = -EKEYREJECTED;
 446                         continue;
 447                 }
 448                 if (ret < 0) {
 449                         if (ret == -ENOPKG) {
 450                                 sinfo->unsupported_crypto = true;
 451                                 continue;
 452                         }
 453                         kleave(" = %d", ret);
 454                         return ret;
 455                 }
 456                 actual_ret = 0;
 457         }
 458
 459         kleave(" = %d", actual_ret);
 460         return actual_ret;
 461 }
 462 EXPORT_SYMBOL_GPL(pkcs7_verify);
 463
 464 /**
 465  * pkcs7_supply_detached_data - Supply the data needed to verify a PKCS#7 message
 466  * @pkcs7: The PKCS#7 message
 467  * @data: The data to be verified
 468  * @datalen: The amount of data
 469  *
 470  * Supply the detached data needed to verify a PKCS#7 message.  Note that no
 471  * attempt to retain/pin the data is made.  That is left to the caller.  The
 472  * data will not be modified by pkcs7_verify() and will not be freed when the
 473  * PKCS#7 message is freed.
 474  *
 475  * Returns -EINVAL if data is already supplied in the message, 0 otherwise.
 476  */
 477 int pkcs7_supply_detached_data(struct pkcs7_message *pkcs7,
 478                                const void *data, size_t datalen)
 479 {
 480         if (pkcs7->data) {
 481                 pr_warn("Data already supplied\n");
 482                 return -EINVAL;
 483         }
 484         pkcs7->data = data;
 485         pkcs7->data_len = datalen;
 486         return 0;
 487 }
 488 EXPORT_SYMBOL_GPL(pkcs7_supply_detached_data);