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/public_key.h>
  16 #include "pkcs7_parser.h"
  17
  18 /*
  19  * Digest the relevant parts of the PKCS#7 data
  20  */
  21 static int pkcs7_digest(struct pkcs7_message *pkcs7,
  22                         struct pkcs7_signed_info *sinfo)
  23 {
  24         struct public_key_signature *sig = sinfo->sig;
  25         struct crypto_shash *tfm;
  26         struct shash_desc *desc;
  27         size_t desc_size;
  28         int ret;
  29
  30         kenter(",%u,%s", sinfo->index, sinfo->sig->hash_algo);
  31
  32         if (!sinfo->sig->hash_algo)
  33                 return -ENOPKG;
  34
  35         /* Allocate the hashing algorithm we're going to need and find out how
  36          * big the hash operational data will be.
  37          */
  38         tfm = crypto_alloc_shash(sinfo->sig->hash_algo, 0, 0);
  39         if (IS_ERR(tfm))
  40                 return (PTR_ERR(tfm) == -ENOENT) ? -ENOPKG : PTR_ERR(tfm);
  41
  42         desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
  43         sig->digest_size = crypto_shash_digestsize(tfm);
  44
  45         ret = -ENOMEM;
  46         sig->digest = kmalloc(sig->digest_size, GFP_KERNEL);
  47         if (!sig->digest)
  48                 goto error_no_desc;
  49
  50         desc = kzalloc(desc_size, GFP_KERNEL);
  51         if (!desc)
  52                 goto error_no_desc;
  53
  54         desc->tfm   = tfm;
  55
  56         /* Digest the message [RFC2315 9.3] */
  57         ret = crypto_shash_digest(desc, pkcs7->data, pkcs7->data_len,
  58                                   sig->digest);
  59         if (ret < 0)
  60                 goto error;
  61         pr_devel("MsgDigest = [%*ph]\n", 8, sig->digest);
  62
  63         /* However, if there are authenticated attributes, there must be a
  64          * message digest attribute amongst them which corresponds to the
  65          * digest we just calculated.
  66          */
  67         if (sinfo->authattrs) {
  68                 u8 tag;
  69
  70                 if (!sinfo->msgdigest) {
  71                         pr_warn("Sig %u: No messageDigest\n", sinfo->index);
  72                         ret = -EKEYREJECTED;
  73                         goto error;
  74                 }
  75
  76                 if (sinfo->msgdigest_len != sig->digest_size) {
  77                         pr_debug("Sig %u: Invalid digest size (%u)\n",
  78                                  sinfo->index, sinfo->msgdigest_len);
  79                         ret = -EBADMSG;
  80                         goto error;
  81                 }
  82
  83                 if (memcmp(sig->digest, sinfo->msgdigest,
  84                            sinfo->msgdigest_len) != 0) {
  85                         pr_debug("Sig %u: Message digest doesn't match\n",
  86                                  sinfo->index);
  87                         ret = -EKEYREJECTED;
  88                         goto error;
  89                 }
  90
  91                 /* We then calculate anew, using the authenticated attributes
  92                  * as the contents of the digest instead.  Note that we need to
  93                  * convert the attributes from a CONT.0 into a SET before we
  94                  * hash it.
  95                  */
  96                 memset(sig->digest, 0, sig->digest_size);
  97
  98                 ret = crypto_shash_init(desc);
  99                 if (ret < 0)
 100                         goto error;
 101                 tag = ASN1_CONS_BIT | ASN1_SET;
 102                 ret = crypto_shash_update(desc, &tag, 1);
 103                 if (ret < 0)
 104                         goto error;
 105                 ret = crypto_shash_finup(desc, sinfo->authattrs,
 106                                          sinfo->authattrs_len, sig->digest);
 107                 if (ret < 0)
 108                         goto error;
 109                 pr_devel("AADigest = [%*ph]\n", 8, sig->digest);
 110         }
 111
 112 error:
 113         kfree(desc);
 114 error_no_desc:
 115         crypto_free_shash(tfm);
 116         kleave(" = %d", ret);
 117         return ret;
 118 }
 119
 120 /*
 121  * Find the key (X.509 certificate) to use to verify a PKCS#7 message.  PKCS#7
 122  * uses the issuer's name and the issuing certificate serial number for
 123  * matching purposes.  These must match the certificate issuer's name (not
 124  * subject's name) and the certificate serial number [RFC 2315 6.7].
 125  */
 126 static int pkcs7_find_key(struct pkcs7_message *pkcs7,
 127                           struct pkcs7_signed_info *sinfo)
 128 {
 129         struct x509_certificate *x509;
 130         unsigned certix = 1;
 131
 132         kenter("%u", sinfo->index);
 133
 134         for (x509 = pkcs7->certs; x509; x509 = x509->next, certix++) {
 135                 /* I'm _assuming_ that the generator of the PKCS#7 message will
 136                  * encode the fields from the X.509 cert in the same way in the
 137                  * PKCS#7 message - but I can't be 100% sure of that.  It's
 138                  * possible this will need element-by-element comparison.
 139                  */
 140                 if (!asymmetric_key_id_same(x509->id, sinfo->sig->auth_ids[0]))
 141                         continue;
 142                 pr_devel("Sig %u: Found cert serial match X.509[%u]\n",
 143                          sinfo->index, certix);
 144
 145                 if (strcmp(x509->pub->pkey_algo, sinfo->sig->pkey_algo) != 0) {
 146                         pr_warn("Sig %u: X.509 algo and PKCS#7 sig algo don't match\n",
 147                                 sinfo->index);
 148                         continue;
 149                 }
 150
 151                 sinfo->signer = x509;
 152                 return 0;
 153         }
 154
 155         /* The relevant X.509 cert isn't found here, but it might be found in
 156          * the trust keyring.
 157          */
 158         pr_debug("Sig %u: Issuing X.509 cert not found (#%*phN)\n",
 159                  sinfo->index,
 160                  sinfo->sig->auth_ids[0]->len, sinfo->sig->auth_ids[0]->data);
 161         return 0;
 162 }
 163
 164 /*
 165  * Verify the internal certificate chain as best we can.
 166  */
 167 static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7,
 168                                   struct pkcs7_signed_info *sinfo)
 169 {
 170         struct public_key_signature *sig;
 171         struct x509_certificate *x509 = sinfo->signer, *p;
 172         struct asymmetric_key_id *auth;
 173         int ret;
 174
 175         kenter("");
 176
 177         for (p = pkcs7->certs; p; p = p->next)
 178                 p->seen = false;
 179
 180         for (;;) {
 181                 pr_debug("verify %s: %*phN\n",
 182                          x509->subject,
 183                          x509->raw_serial_size, x509->raw_serial);
 184                 x509->seen = true;
 185
 186                 if (x509->blacklisted) {
 187                         /* If this cert is blacklisted, then mark everything
 188                          * that depends on this as blacklisted too.
 189                          */
 190                         sinfo->blacklisted = true;
 191                         for (p = sinfo->signer; p != x509; p = p->signer)
 192                                 p->blacklisted = true;
 193                         pr_debug("- blacklisted\n");
 194                         return 0;
 195                 }
 196
 197                 if (x509->unsupported_key)
 198                         goto unsupported_crypto_in_x509;
 199
 200                 pr_debug("- issuer %s\n", x509->issuer);
 201                 sig = x509->sig;
 202                 if (sig->auth_ids[0])
 203                         pr_debug("- authkeyid.id %*phN\n",
 204                                  sig->auth_ids[0]->len, sig->auth_ids[0]->data);
 205                 if (sig->auth_ids[1])
 206                         pr_debug("- authkeyid.skid %*phN\n",
 207                                  sig->auth_ids[1]->len, sig->auth_ids[1]->data);
 208
 209                 if (x509->self_signed) {
 210                         /* If there's no authority certificate specified, then
 211                          * the certificate must be self-signed and is the root
 212                          * of the chain.  Likewise if the cert is its own
 213                          * authority.
 214                          */
 215                         if (x509->unsupported_sig)
 216                                 goto unsupported_crypto_in_x509;
 217                         x509->signer = x509;
 218                         pr_debug("- self-signed\n");
 219                         return 0;
 220                 }
 221
 222                 /* Look through the X.509 certificates in the PKCS#7 message's
 223                  * list to see if the next one is there.
 224                  */
 225                 auth = sig->auth_ids[0];
 226                 if (auth) {
 227                         pr_debug("- want %*phN\n", auth->len, auth->data);
 228                         for (p = pkcs7->certs; p; p = p->next) {
 229                                 pr_debug("- cmp [%u] %*phN\n",
 230                                          p->index, p->id->len, p->id->data);
 231                                 if (asymmetric_key_id_same(p->id, auth))
 232                                         goto found_issuer_check_skid;
 233                         }
 234                 } else if (sig->auth_ids[1]) {
 235                         auth = sig->auth_ids[1];
 236                         pr_debug("- want %*phN\n", auth->len, auth->data);
 237                         for (p = pkcs7->certs; p; p = p->next) {
 238                                 if (!p->skid)
 239                                         continue;
 240                                 pr_debug("- cmp [%u] %*phN\n",
 241                                          p->index, p->skid->len, p->skid->data);
 242                                 if (asymmetric_key_id_same(p->skid, auth))
 243                                         goto found_issuer;
 244                         }
 245                 }
 246
 247                 /* We didn't find the root of this chain */
 248                 pr_debug("- top\n");
 249                 return 0;
 250
 251         found_issuer_check_skid:
 252                 /* We matched issuer + serialNumber, but if there's an
 253                  * authKeyId.keyId, that must match the CA subjKeyId also.
 254                  */
 255                 if (sig->auth_ids[1] &&
 256                     !asymmetric_key_id_same(p->skid, sig->auth_ids[1])) {
 257                         pr_warn("Sig %u: X.509 chain contains auth-skid nonmatch (%u->%u)\n",
 258                                 sinfo->index, x509->index, p->index);
 259                         return -EKEYREJECTED;
 260                 }
 261         found_issuer:
 262                 pr_debug("- subject %s\n", p->subject);
 263                 if (p->seen) {
 264                         pr_warn("Sig %u: X.509 chain contains loop\n",
 265                                 sinfo->index);
 266                         return 0;
 267                 }
 268                 ret = public_key_verify_signature(p->pub, x509->sig);
 269                 if (ret < 0)
 270                         return ret;
 271                 x509->signer = p;
 272                 if (x509 == p) {
 273                         pr_debug("- self-signed\n");
 274                         return 0;
 275                 }
 276                 x509 = p;
 277                 might_sleep();
 278         }
 279
 280 unsupported_crypto_in_x509:
 281         /* Just prune the certificate chain at this point if we lack some
 282          * crypto module to go further.  Note, however, we don't want to set
 283          * sinfo->unsupported_crypto as the signed info block may still be
 284          * validatable against an X.509 cert lower in the chain that we have a
 285          * trusted copy of.
 286          */
 287         return 0;
 288 }
 289
 290 /*
 291  * Verify one signed information block from a PKCS#7 message.
 292  */
 293 static int pkcs7_verify_one(struct pkcs7_message *pkcs7,
 294                             struct pkcs7_signed_info *sinfo)
 295 {
 296         int ret;
 297
 298         kenter(",%u", sinfo->index);
 299
 300         /* First of all, digest the data in the PKCS#7 message and the
 301          * signed information block
 302          */
 303         ret = pkcs7_digest(pkcs7, sinfo);
 304         if (ret < 0)
 305                 return ret;
 306
 307         /* Find the key for the signature if there is one */
 308         ret = pkcs7_find_key(pkcs7, sinfo);
 309         if (ret < 0)
 310                 return ret;
 311
 312         if (!sinfo->signer)
 313                 return 0;
 314
 315         pr_devel("Using X.509[%u] for sig %u\n",
 316                  sinfo->signer->index, sinfo->index);
 317
 318         /* Check that the PKCS#7 signing time is valid according to the X.509
 319          * certificate.  We can't, however, check against the system clock
 320          * since that may not have been set yet and may be wrong.
 321          */
 322         if (test_bit(sinfo_has_signing_time, &sinfo->aa_set)) {
 323                 if (sinfo->signing_time < sinfo->signer->valid_from ||
 324                     sinfo->signing_time > sinfo->signer->valid_to) {
 325                         pr_warn("Message signed outside of X.509 validity window\n");
 326                         return -EKEYREJECTED;
 327                 }
 328         }
 329
 330         /* Verify the PKCS#7 binary against the key */
 331         ret = public_key_verify_signature(sinfo->signer->pub, sinfo->sig);
 332         if (ret < 0)
 333                 return ret;
 334
 335         pr_devel("Verified signature %u\n", sinfo->index);
 336
 337         /* Verify the internal certificate chain */
 338         return pkcs7_verify_sig_chain(pkcs7, sinfo);
 339 }
 340
 341 /**
 342  * pkcs7_verify - Verify a PKCS#7 message
 343  * @pkcs7: The PKCS#7 message to be verified
 344  * @usage: The use to which the key is being put
 345  *
 346  * Verify a PKCS#7 message is internally consistent - that is, the data digest
 347  * matches the digest in the AuthAttrs and any signature in the message or one
 348  * of the X.509 certificates it carries that matches another X.509 cert in the
 349  * message can be verified.
 350  *
 351  * This does not look to match the contents of the PKCS#7 message against any
 352  * external public keys.
 353  *
 354  * Returns, in order of descending priority:
 355  *
 356  *  (*) -EKEYREJECTED if a key was selected that had a usage restriction at
 357  *      odds with the specified usage, or:
 358  *
 359  *  (*) -EKEYREJECTED if a signature failed to match for which we found an
 360  *      appropriate X.509 certificate, or:
 361  *
 362  *  (*) -EBADMSG if some part of the message was invalid, or:
 363  *
 364  *  (*) 0 if a signature chain passed verification, or:
 365  *
 366  *  (*) -EKEYREJECTED if a blacklisted key was encountered, or:
 367  *
 368  *  (*) -ENOPKG if none of the signature chains are verifiable because suitable
 369  *      crypto modules couldn't be found.
 370  */
 371 int pkcs7_verify(struct pkcs7_message *pkcs7,
 372                  enum key_being_used_for usage)
 373 {
 374         struct pkcs7_signed_info *sinfo;
 375         int actual_ret = -ENOPKG;
 376         int ret;
 377
 378         kenter("");
 379
 380         switch (usage) {
 381         case VERIFYING_MODULE_SIGNATURE:
 382                 if (pkcs7->data_type != OID_data) {
 383                         pr_warn("Invalid module sig (not pkcs7-data)\n");
 384                         return -EKEYREJECTED;
 385                 }
 386                 if (pkcs7->have_authattrs) {
 387                         pr_warn("Invalid module sig (has authattrs)\n");
 388                         return -EKEYREJECTED;
 389                 }
 390                 break;
 391         case VERIFYING_FIRMWARE_SIGNATURE:
 392                 if (pkcs7->data_type != OID_data) {
 393                         pr_warn("Invalid firmware sig (not pkcs7-data)\n");
 394                         return -EKEYREJECTED;
 395                 }
 396                 if (!pkcs7->have_authattrs) {
 397                         pr_warn("Invalid firmware sig (missing authattrs)\n");
 398                         return -EKEYREJECTED;
 399                 }
 400                 break;
 401         case VERIFYING_KEXEC_PE_SIGNATURE:
 402                 if (pkcs7->data_type != OID_msIndirectData) {
 403                         pr_warn("Invalid kexec sig (not Authenticode)\n");
 404                         return -EKEYREJECTED;
 405                 }
 406                 /* Authattr presence checked in parser */
 407                 break;
 408         case VERIFYING_UNSPECIFIED_SIGNATURE:
 409                 if (pkcs7->data_type != OID_data) {
 410                         pr_warn("Invalid unspecified sig (not pkcs7-data)\n");
 411                         return -EKEYREJECTED;
 412                 }
 413                 break;
 414         default:
 415                 return -EINVAL;
 416         }
 417
 418         for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
 419                 ret = pkcs7_verify_one(pkcs7, sinfo);
 420                 if (sinfo->blacklisted) {
 421                         if (actual_ret == -ENOPKG)
 422                                 actual_ret = -EKEYREJECTED;
 423                         continue;
 424                 }
 425                 if (ret < 0) {
 426                         if (ret == -ENOPKG) {
 427                                 sinfo->unsupported_crypto = true;
 428                                 continue;
 429                         }
 430                         kleave(" = %d", ret);
 431                         return ret;
 432                 }
 433                 actual_ret = 0;
 434         }
 435
 436         kleave(" = %d", actual_ret);
 437         return actual_ret;
 438 }
 439 EXPORT_SYMBOL_GPL(pkcs7_verify);
 440
 441 /**
 442  * pkcs7_supply_detached_data - Supply the data needed to verify a PKCS#7 message
 443  * @pkcs7: The PKCS#7 message
 444  * @data: The data to be verified
 445  * @datalen: The amount of data
 446  *
 447  * Supply the detached data needed to verify a PKCS#7 message.  Note that no
 448  * attempt to retain/pin the data is made.  That is left to the caller.  The
 449  * data will not be modified by pkcs7_verify() and will not be freed when the
 450  * PKCS#7 message is freed.
 451  *
 452  * Returns -EINVAL if data is already supplied in the message, 0 otherwise.
 453  */
 454 int pkcs7_supply_detached_data(struct pkcs7_message *pkcs7,
 455                                const void *data, size_t datalen)
 456 {
 457         if (pkcs7->data) {
 458                 pr_debug("Data already supplied\n");
 459                 return -EINVAL;
 460         }
 461         pkcs7->data = data;
 462         pkcs7->data_len = datalen;
 463         return 0;
 464 }