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 "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 crypto_shash *tfm;
  29         struct shash_desc *desc;
  30         size_t digest_size, desc_size;
  31         void *digest;
  32         int ret;
  33
  34         kenter(",%u,%u", sinfo->index, sinfo->sig.pkey_hash_algo);
  35
  36         if (sinfo->sig.pkey_hash_algo >= PKEY_HASH__LAST ||
  37             !hash_algo_name[sinfo->sig.pkey_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(hash_algo_name[sinfo->sig.pkey_hash_algo],
  44                                  0, 0);
  45         if (IS_ERR(tfm))
  46                 return (PTR_ERR(tfm) == -ENOENT) ? -ENOPKG : PTR_ERR(tfm);
  47
  48         desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
  49         sinfo->sig.digest_size = digest_size = crypto_shash_digestsize(tfm);
  50
  51         ret = -ENOMEM;
  52         digest = kzalloc(digest_size + desc_size, GFP_KERNEL);
  53         if (!digest)
  54                 goto error_no_desc;
  55
  56         desc = digest + digest_size;
  57         desc->tfm   = tfm;
  58         desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
  59
  60         /* Digest the message [RFC2315 9.3] */
  61         ret = crypto_shash_init(desc);
  62         if (ret < 0)
  63                 goto error;
  64         ret = crypto_shash_finup(desc, pkcs7->data, pkcs7->data_len, digest);
  65         if (ret < 0)
  66                 goto error;
  67         pr_devel("MsgDigest = [%*ph]\n", 8, digest);
  68
  69         /* However, if there are authenticated attributes, there must be a
  70          * message digest attribute amongst them which corresponds to the
  71          * digest we just calculated.
  72          */
  73         if (sinfo->msgdigest) {
  74                 u8 tag;
  75
  76                 if (sinfo->msgdigest_len != sinfo->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(digest, sinfo->msgdigest, sinfo->msgdigest_len) != 0) {
  84                         pr_debug("Sig %u: Message digest doesn't match\n",
  85                                  sinfo->index);
  86                         ret = -EKEYREJECTED;
  87                         goto error;
  88                 }
  89
  90                 /* We then calculate anew, using the authenticated attributes
  91                  * as the contents of the digest instead.  Note that we need to
  92                  * convert the attributes from a CONT.0 into a SET before we
  93                  * hash it.
  94                  */
  95                 memset(digest, 0, sinfo->sig.digest_size);
  96
  97                 ret = crypto_shash_init(desc);
  98                 if (ret < 0)
  99                         goto error;
 100                 tag = ASN1_CONS_BIT | ASN1_SET;
 101                 ret = crypto_shash_update(desc, &tag, 1);
 102                 if (ret < 0)
 103                         goto error;
 104                 ret = crypto_shash_finup(desc, sinfo->authattrs,
 105                                          sinfo->authattrs_len, digest);
 106                 if (ret < 0)
 107                         goto error;
 108                 pr_devel("AADigest = [%*ph]\n", 8, digest);
 109         }
 110
 111         sinfo->sig.digest = digest;
 112         digest = NULL;
 113
 114 error:
 115         kfree(digest);
 116 error_no_desc:
 117         crypto_free_shash(tfm);
 118         kleave(" = %d", ret);
 119         return ret;
 120 }
 121
 122 /*
 123  * Find the key (X.509 certificate) to use to verify a PKCS#7 message.  PKCS#7
 124  * uses the issuer's name and the issuing certificate serial number for
 125  * matching purposes.  These must match the certificate issuer's name (not
 126  * subject's name) and the certificate serial number [RFC 2315 6.7].
 127  */
 128 static int pkcs7_find_key(struct pkcs7_message *pkcs7,
 129                           struct pkcs7_signed_info *sinfo)
 130 {
 131         struct x509_certificate *x509;
 132         unsigned certix = 1;
 133
 134         kenter("%u", sinfo->index);
 135
 136         for (x509 = pkcs7->certs; x509; x509 = x509->next, certix++) {
 137                 /* I'm _assuming_ that the generator of the PKCS#7 message will
 138                  * encode the fields from the X.509 cert in the same way in the
 139                  * PKCS#7 message - but I can't be 100% sure of that.  It's
 140                  * possible this will need element-by-element comparison.
 141                  */
 142                 if (!asymmetric_key_id_same(x509->id, sinfo->signing_cert_id))
 143                         continue;
 144                 pr_devel("Sig %u: Found cert serial match X.509[%u]\n",
 145                          sinfo->index, certix);
 146
 147                 if (x509->pub->pkey_algo != sinfo->sig.pkey_algo) {
 148                         pr_warn("Sig %u: X.509 algo and PKCS#7 sig algo don't match\n",
 149                                 sinfo->index);
 150                         continue;
 151                 }
 152
 153                 sinfo->signer = x509;
 154                 return 0;
 155         }
 156
 157         /* The relevant X.509 cert isn't found here, but it might be found in
 158          * the trust keyring.
 159          */
 160         pr_debug("Sig %u: Issuing X.509 cert not found (#%*phN)\n",
 161                  sinfo->index,
 162                  sinfo->signing_cert_id->len, sinfo->signing_cert_id->data);
 163         return 0;
 164 }
 165
 166 /*
 167  * Verify the internal certificate chain as best we can.
 168  */
 169 static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7,
 170                                   struct pkcs7_signed_info *sinfo)
 171 {
 172         struct x509_certificate *x509 = sinfo->signer, *p;
 173         struct asymmetric_key_id *auth;
 174         int ret;
 175
 176         kenter("");
 177
 178         for (p = pkcs7->certs; p; p = p->next)
 179                 p->seen = false;
 180
 181         for (;;) {
 182                 pr_debug("verify %s: %*phN\n",
 183                          x509->subject,
 184                          x509->raw_serial_size, x509->raw_serial);
 185                 x509->seen = true;
 186                 ret = x509_get_sig_params(x509);
 187                 if (ret < 0)
 188                         goto maybe_missing_crypto_in_x509;
 189
 190                 pr_debug("- issuer %s\n", x509->issuer);
 191                 if (x509->akid_id)
 192                         pr_debug("- authkeyid.id %*phN\n",
 193                                  x509->akid_id->len, x509->akid_id->data);
 194                 if (x509->akid_skid)
 195                         pr_debug("- authkeyid.skid %*phN\n",
 196                                  x509->akid_skid->len, x509->akid_skid->data);
 197
 198                 if ((!x509->akid_id && !x509->akid_skid) ||
 199                     strcmp(x509->subject, x509->issuer) == 0) {
 200                         /* If there's no authority certificate specified, then
 201                          * the certificate must be self-signed and is the root
 202                          * of the chain.  Likewise if the cert is its own
 203                          * authority.
 204                          */
 205                         pr_debug("- no auth?\n");
 206                         if (x509->raw_subject_size != x509->raw_issuer_size ||
 207                             memcmp(x509->raw_subject, x509->raw_issuer,
 208                                    x509->raw_issuer_size) != 0)
 209                                 return 0;
 210
 211                         ret = x509_check_signature(x509->pub, x509);
 212                         if (ret < 0)
 213                                 goto maybe_missing_crypto_in_x509;
 214                         x509->signer = x509;
 215                         pr_debug("- self-signed\n");
 216                         return 0;
 217                 }
 218
 219                 /* Look through the X.509 certificates in the PKCS#7 message's
 220                  * list to see if the next one is there.
 221                  */
 222                 auth = x509->akid_id;
 223                 if (auth) {
 224                         pr_debug("- want %*phN\n", auth->len, auth->data);
 225                         for (p = pkcs7->certs; p; p = p->next) {
 226                                 pr_debug("- cmp [%u] %*phN\n",
 227                                          p->index, p->id->len, p->id->data);
 228                                 if (asymmetric_key_id_same(p->id, auth))
 229                                         goto found_issuer_check_skid;
 230                         }
 231                 } else {
 232                         auth = x509->akid_skid;
 233                         pr_debug("- want %*phN\n", auth->len, auth->data);
 234                         for (p = pkcs7->certs; p; p = p->next) {
 235                                 if (!p->skid)
 236                                         continue;
 237                                 pr_debug("- cmp [%u] %*phN\n",
 238                                          p->index, p->skid->len, p->skid->data);
 239                                 if (asymmetric_key_id_same(p->skid, auth))
 240                                         goto found_issuer;
 241                         }
 242                 }
 243
 244                 /* We didn't find the root of this chain */
 245                 pr_debug("- top\n");
 246                 return 0;
 247
 248         found_issuer_check_skid:
 249                 /* We matched issuer + serialNumber, but if there's an
 250                  * authKeyId.keyId, that must match the CA subjKeyId also.
 251                  */
 252                 if (x509->akid_skid &&
 253                     !asymmetric_key_id_same(p->skid, x509->akid_skid)) {
 254                         pr_warn("Sig %u: X.509 chain contains auth-skid nonmatch (%u->%u)\n",
 255                                 sinfo->index, x509->index, p->index);
 256                         return -EKEYREJECTED;
 257                 }
 258         found_issuer:
 259                 pr_debug("- subject %s\n", p->subject);
 260                 if (p->seen) {
 261                         pr_warn("Sig %u: X.509 chain contains loop\n",
 262                                 sinfo->index);
 263                         return 0;
 264                 }
 265                 ret = x509_check_signature(p->pub, x509);
 266                 if (ret < 0)
 267                         return ret;
 268                 x509->signer = p;
 269                 if (x509 == p) {
 270                         pr_debug("- self-signed\n");
 271                         return 0;
 272                 }
 273                 x509 = p;
 274                 might_sleep();
 275         }
 276
 277 maybe_missing_crypto_in_x509:
 278         /* Just prune the certificate chain at this point if we lack some
 279          * crypto module to go further.  Note, however, we don't want to set
 280          * sinfo->missing_crypto as the signed info block may still be
 281          * validatable against an X.509 cert lower in the chain that we have a
 282          * trusted copy of.
 283          */
 284         if (ret == -ENOPKG)
 285                 return 0;
 286         return ret;
 287 }
 288
 289 /*
 290  * Verify one signed information block from a PKCS#7 message.
 291  */
 292 static int pkcs7_verify_one(struct pkcs7_message *pkcs7,
 293                             struct pkcs7_signed_info *sinfo)
 294 {
 295         int ret;
 296
 297         kenter(",%u", sinfo->index);
 298
 299         /* First of all, digest the data in the PKCS#7 message and the
 300          * signed information block
 301          */
 302         ret = pkcs7_digest(pkcs7, sinfo);
 303         if (ret < 0)
 304                 return ret;
 305
 306         /* Find the key for the signature if there is one */
 307         ret = pkcs7_find_key(pkcs7, sinfo);
 308         if (ret < 0)
 309                 return ret;
 310
 311         if (!sinfo->signer)
 312                 return 0;
 313
 314         pr_devel("Using X.509[%u] for sig %u\n",
 315                  sinfo->signer->index, sinfo->index);
 316
 317         /* Verify the PKCS#7 binary against the key */
 318         ret = public_key_verify_signature(sinfo->signer->pub, &sinfo->sig);
 319         if (ret < 0)
 320                 return ret;
 321
 322         pr_devel("Verified signature %u\n", sinfo->index);
 323
 324         /* Verify the internal certificate chain */
 325         return pkcs7_verify_sig_chain(pkcs7, sinfo);
 326 }
 327
 328 /**
 329  * pkcs7_verify - Verify a PKCS#7 message
 330  * @pkcs7: The PKCS#7 message to be verified
 331  *
 332  * Verify a PKCS#7 message is internally consistent - that is, the data digest
 333  * matches the digest in the AuthAttrs and any signature in the message or one
 334  * of the X.509 certificates it carries that matches another X.509 cert in the
 335  * message can be verified.
 336  *
 337  * This does not look to match the contents of the PKCS#7 message against any
 338  * external public keys.
 339  *
 340  * Returns, in order of descending priority:
 341  *
 342  *  (*) -EKEYREJECTED if a signature failed to match for which we found an
 343  *      appropriate X.509 certificate, or:
 344  *
 345  *  (*) -EBADMSG if some part of the message was invalid, or:
 346  *
 347  *  (*) -ENOPKG if none of the signature chains are verifiable because suitable
 348  *      crypto modules couldn't be found, or:
 349  *
 350  *  (*) 0 if all the signature chains that don't incur -ENOPKG can be verified
 351  *      (note that a signature chain may be of zero length), or:
 352  */
 353 int pkcs7_verify(struct pkcs7_message *pkcs7)
 354 {
 355         struct pkcs7_signed_info *sinfo;
 356         struct x509_certificate *x509;
 357         int enopkg = -ENOPKG;
 358         int ret, n;
 359
 360         kenter("");
 361
 362         for (n = 0, x509 = pkcs7->certs; x509; x509 = x509->next, n++) {
 363                 ret = x509_get_sig_params(x509);
 364                 if (ret < 0)
 365                         return ret;
 366         }
 367
 368         for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
 369                 ret = pkcs7_verify_one(pkcs7, sinfo);
 370                 if (ret < 0) {
 371                         if (ret == -ENOPKG) {
 372                                 sinfo->unsupported_crypto = true;
 373                                 continue;
 374                         }
 375                         kleave(" = %d", ret);
 376                         return ret;
 377                 }
 378                 enopkg = 0;
 379         }
 380
 381         kleave(" = %d", enopkg);
 382         return enopkg;
 383 }
 384 EXPORT_SYMBOL_GPL(pkcs7_verify);