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_init(desc);
  63         if (ret < 0)
  64                 goto error;
  65         ret = crypto_shash_finup(desc, pkcs7->data, pkcs7->data_len,
  66                                  sig->digest);
  67         if (ret < 0)
  68                 goto error;
  69         pr_devel("MsgDigest = [%*ph]\n", 8, sig->digest);
  70
  71         /* However, if there are authenticated attributes, there must be a
  72          * message digest attribute amongst them which corresponds to the
  73          * digest we just calculated.
  74          */
  75         if (sinfo->authattrs) {
  76                 u8 tag;
  77
  78                 if (!sinfo->msgdigest) {
  79                         pr_warn("Sig %u: No messageDigest\n", sinfo->index);
  80                         ret = -EKEYREJECTED;
  81                         goto error;
  82                 }
  83
  84                 if (sinfo->msgdigest_len != sig->digest_size) {
  85                         pr_debug("Sig %u: Invalid digest size (%u)\n",
  86                                  sinfo->index, sinfo->msgdigest_len);
  87                         ret = -EBADMSG;
  88                         goto error;
  89                 }
  90
  91                 if (memcmp(sig->digest, sinfo->msgdigest,
  92                            sinfo->msgdigest_len) != 0) {
  93                         pr_debug("Sig %u: Message digest doesn't match\n",
  94                                  sinfo->index);
  95                         ret = -EKEYREJECTED;
  96                         goto error;
  97                 }
  98
  99                 /* We then calculate anew, using the authenticated attributes
 100                  * as the contents of the digest instead.  Note that we need to
 101                  * convert the attributes from a CONT.0 into a SET before we
 102                  * hash it.
 103                  */
 104                 memset(sig->digest, 0, sig->digest_size);
 105
 106                 ret = crypto_shash_init(desc);
 107                 if (ret < 0)
 108                         goto error;
 109                 tag = ASN1_CONS_BIT | ASN1_SET;
 110                 ret = crypto_shash_update(desc, &tag, 1);
 111                 if (ret < 0)
 112                         goto error;
 113                 ret = crypto_shash_finup(desc, sinfo->authattrs,
 114                                          sinfo->authattrs_len, sig->digest);
 115                 if (ret < 0)
 116                         goto error;
 117                 pr_devel("AADigest = [%*ph]\n", 8, sig->digest);
 118         }
 119
 120 error:
 121         kfree(desc);
 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->sig->auth_ids[0]))
 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->sig->auth_ids[0]->len, sinfo->sig->auth_ids[0]->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 public_key_signature *sig;
 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
 194                 if (x509->blacklisted) {
 195                         /* If this cert is blacklisted, then mark everything
 196                          * that depends on this as blacklisted too.
 197                          */
 198                         sinfo->blacklisted = true;
 199                         for (p = sinfo->signer; p != x509; p = p->signer)
 200                                 p->blacklisted = true;
 201                         pr_debug("- blacklisted\n");
 202                         return 0;
 203                 }
 204
 205                 if (x509->unsupported_key)
 206                         goto unsupported_crypto_in_x509;
 207
 208                 pr_debug("- issuer %s\n", x509->issuer);
 209                 sig = x509->sig;
 210                 if (sig->auth_ids[0])
 211                         pr_debug("- authkeyid.id %*phN\n",
 212                                  sig->auth_ids[0]->len, sig->auth_ids[0]->data);
 213                 if (sig->auth_ids[1])
 214                         pr_debug("- authkeyid.skid %*phN\n",
 215                                  sig->auth_ids[1]->len, sig->auth_ids[1]->data);
 216
 217                 if (x509->self_signed) {
 218                         /* If there's no authority certificate specified, then
 219                          * the certificate must be self-signed and is the root
 220                          * of the chain.  Likewise if the cert is its own
 221                          * authority.
 222                          */
 223                         if (x509->unsupported_sig)
 224                                 goto unsupported_crypto_in_x509;
 225                         x509->signer = x509;
 226                         pr_debug("- self-signed\n");
 227                         return 0;
 228                 }
 229
 230                 /* Look through the X.509 certificates in the PKCS#7 message's
 231                  * list to see if the next one is there.
 232                  */
 233                 auth = sig->auth_ids[0];
 234                 if (auth) {
 235                         pr_debug("- want %*phN\n", auth->len, auth->data);
 236                         for (p = pkcs7->certs; p; p = p->next) {
 237                                 pr_debug("- cmp [%u] %*phN\n",
 238                                          p->index, p->id->len, p->id->data);
 239                                 if (asymmetric_key_id_same(p->id, auth))
 240                                         goto found_issuer_check_skid;
 241                         }
 242                 } else if (sig->auth_ids[1]) {
 243                         auth = sig->auth_ids[1];
 244                         pr_debug("- want %*phN\n", auth->len, auth->data);
 245                         for (p = pkcs7->certs; p; p = p->next) {
 246                                 if (!p->skid)
 247                                         continue;
 248                                 pr_debug("- cmp [%u] %*phN\n",
 249                                          p->index, p->skid->len, p->skid->data);
 250                                 if (asymmetric_key_id_same(p->skid, auth))
 251                                         goto found_issuer;
 252                         }
 253                 }
 254
 255                 /* We didn't find the root of this chain */
 256                 pr_debug("- top\n");
 257                 return 0;
 258
 259         found_issuer_check_skid:
 260                 /* We matched issuer + serialNumber, but if there's an
 261                  * authKeyId.keyId, that must match the CA subjKeyId also.
 262                  */
 263                 if (sig->auth_ids[1] &&
 264                     !asymmetric_key_id_same(p->skid, sig->auth_ids[1])) {
 265                         pr_warn("Sig %u: X.509 chain contains auth-skid nonmatch (%u->%u)\n",
 266                                 sinfo->index, x509->index, p->index);
 267                         return -EKEYREJECTED;
 268                 }
 269         found_issuer:
 270                 pr_debug("- subject %s\n", p->subject);
 271                 if (p->seen) {
 272                         pr_warn("Sig %u: X.509 chain contains loop\n",
 273                                 sinfo->index);
 274                         return 0;
 275                 }
 276                 ret = public_key_verify_signature(p->pub, p->sig);
 277                 if (ret < 0)
 278                         return ret;
 279                 x509->signer = p;
 280                 if (x509 == p) {
 281                         pr_debug("- self-signed\n");
 282                         return 0;
 283                 }
 284                 x509 = p;
 285                 might_sleep();
 286         }
 287
 288 unsupported_crypto_in_x509:
 289         /* Just prune the certificate chain at this point if we lack some
 290          * crypto module to go further.  Note, however, we don't want to set
 291          * sinfo->unsupported_crypto as the signed info block may still be
 292          * validatable against an X.509 cert lower in the chain that we have a
 293          * trusted copy of.
 294          */
 295         return 0;
 296 }
 297
 298 /*
 299  * Verify one signed information block from a PKCS#7 message.
 300  */
 301 static int pkcs7_verify_one(struct pkcs7_message *pkcs7,
 302                             struct pkcs7_signed_info *sinfo)
 303 {
 304         int ret;
 305
 306         kenter(",%u", sinfo->index);
 307
 308         /* First of all, digest the data in the PKCS#7 message and the
 309          * signed information block
 310          */
 311         ret = pkcs7_digest(pkcs7, sinfo);
 312         if (ret < 0)
 313                 return ret;
 314
 315         /* Find the key for the signature if there is one */
 316         ret = pkcs7_find_key(pkcs7, sinfo);
 317         if (ret < 0)
 318                 return ret;
 319
 320         if (!sinfo->signer)
 321                 return 0;
 322
 323         pr_devel("Using X.509[%u] for sig %u\n",
 324                  sinfo->signer->index, sinfo->index);
 325
 326         /* Check that the PKCS#7 signing time is valid according to the X.509
 327          * certificate.  We can't, however, check against the system clock
 328          * since that may not have been set yet and may be wrong.
 329          */
 330         if (test_bit(sinfo_has_signing_time, &sinfo->aa_set)) {
 331                 if (sinfo->signing_time < sinfo->signer->valid_from ||
 332                     sinfo->signing_time > sinfo->signer->valid_to) {
 333                         pr_warn("Message signed outside of X.509 validity window\n");
 334                         return -EKEYREJECTED;
 335                 }
 336         }
 337
 338         /* Verify the PKCS#7 binary against the key */
 339         ret = public_key_verify_signature(sinfo->signer->pub, sinfo->sig);
 340         if (ret < 0)
 341                 return ret;
 342
 343         pr_devel("Verified signature %u\n", sinfo->index);
 344
 345         /* Verify the internal certificate chain */
 346         return pkcs7_verify_sig_chain(pkcs7, sinfo);
 347 }
 348
 349 /**
 350  * pkcs7_verify - Verify a PKCS#7 message
 351  * @pkcs7: The PKCS#7 message to be verified
 352  * @usage: The use to which the key is being put
 353  *
 354  * Verify a PKCS#7 message is internally consistent - that is, the data digest
 355  * matches the digest in the AuthAttrs and any signature in the message or one
 356  * of the X.509 certificates it carries that matches another X.509 cert in the
 357  * message can be verified.
 358  *
 359  * This does not look to match the contents of the PKCS#7 message against any
 360  * external public keys.
 361  *
 362  * Returns, in order of descending priority:
 363  *
 364  *  (*) -EKEYREJECTED if a key was selected that had a usage restriction at
 365  *      odds with the specified usage, or:
 366  *
 367  *  (*) -EKEYREJECTED if a signature failed to match for which we found an
 368  *      appropriate X.509 certificate, or:
 369  *
 370  *  (*) -EBADMSG if some part of the message was invalid, or:
 371  *
 372  *  (*) 0 if no signature chains were found to be blacklisted or to contain
 373  *      unsupported crypto, or:
 374  *
 375  *  (*) -EKEYREJECTED if a blacklisted key was encountered, or:
 376  *
 377  *  (*) -ENOPKG if none of the signature chains are verifiable because suitable
 378  *      crypto modules couldn't be found.
 379  */
 380 int pkcs7_verify(struct pkcs7_message *pkcs7,
 381                  enum key_being_used_for usage)
 382 {
 383         struct pkcs7_signed_info *sinfo;
 384         int actual_ret = -ENOPKG;
 385         int ret;
 386
 387         kenter("");
 388
 389         switch (usage) {
 390         case VERIFYING_MODULE_SIGNATURE:
 391                 if (pkcs7->data_type != OID_data) {
 392                         pr_warn("Invalid module sig (not pkcs7-data)\n");
 393                         return -EKEYREJECTED;
 394                 }
 395                 if (pkcs7->have_authattrs) {
 396                         pr_warn("Invalid module sig (has authattrs)\n");
 397                         return -EKEYREJECTED;
 398                 }
 399                 break;
 400         case VERIFYING_FIRMWARE_SIGNATURE:
 401                 if (pkcs7->data_type != OID_data) {
 402                         pr_warn("Invalid firmware sig (not pkcs7-data)\n");
 403                         return -EKEYREJECTED;
 404                 }
 405                 if (!pkcs7->have_authattrs) {
 406                         pr_warn("Invalid firmware sig (missing authattrs)\n");
 407                         return -EKEYREJECTED;
 408                 }
 409                 break;
 410         case VERIFYING_KEXEC_PE_SIGNATURE:
 411                 if (pkcs7->data_type != OID_msIndirectData) {
 412                         pr_warn("Invalid kexec sig (not Authenticode)\n");
 413                         return -EKEYREJECTED;
 414                 }
 415                 /* Authattr presence checked in parser */
 416                 break;
 417         case VERIFYING_UNSPECIFIED_SIGNATURE:
 418                 if (pkcs7->data_type != OID_data) {
 419                         pr_warn("Invalid unspecified sig (not pkcs7-data)\n");
 420                         return -EKEYREJECTED;
 421                 }
 422                 break;
 423         default:
 424                 return -EINVAL;
 425         }
 426
 427         for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
 428                 ret = pkcs7_verify_one(pkcs7, sinfo);
 429                 if (sinfo->blacklisted && actual_ret == -ENOPKG)
 430                         actual_ret = -EKEYREJECTED;
 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                 actual_ret = 0;
 440         }
 441
 442         kleave(" = %d", actual_ret);
 443         return actual_ret;
 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 }