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         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                 ret = x509_get_sig_params(x509);
 186                 if (ret < 0)
 187                         goto maybe_missing_crypto_in_x509;
 188
 189                 pr_debug("- issuer %s\n", x509->issuer);
 190                 if (x509->akid_skid)
 191                         pr_debug("- authkeyid %*phN\n",
 192                                  x509->akid_skid->len, x509->akid_skid->data);
 193
 194                 if (!x509->akid_skid ||
 195                     strcmp(x509->subject, x509->issuer) == 0) {
 196                         /* If there's no authority certificate specified, then
 197                          * the certificate must be self-signed and is the root
 198                          * of the chain.  Likewise if the cert is its own
 199                          * authority.
 200                          */
 201                         pr_debug("- no auth?\n");
 202                         if (x509->raw_subject_size != x509->raw_issuer_size ||
 203                             memcmp(x509->raw_subject, x509->raw_issuer,
 204                                    x509->raw_issuer_size) != 0)
 205                                 return 0;
 206
 207                         ret = x509_check_signature(x509->pub, x509);
 208                         if (ret < 0)
 209                                 goto maybe_missing_crypto_in_x509;
 210                         x509->signer = x509;
 211                         pr_debug("- self-signed\n");
 212                         return 0;
 213                 }
 214
 215                 /* Look through the X.509 certificates in the PKCS#7 message's
 216                  * list to see if the next one is there.
 217                  */
 218                 pr_debug("- want %*phN\n",
 219                          x509->akid_skid->len, x509->akid_skid->data);
 220                 for (p = pkcs7->certs; p; p = p->next) {
 221                         if (!p->skid)
 222                                 continue;
 223                         pr_debug("- cmp [%u] %*phN\n",
 224                                  p->index, p->skid->len, p->skid->data);
 225                         if (asymmetric_key_id_same(p->skid, x509->akid_skid))
 226                                 goto found_issuer;
 227                 }
 228
 229                 /* We didn't find the root of this chain */
 230                 pr_debug("- top\n");
 231                 return 0;
 232
 233         found_issuer:
 234                 pr_debug("- subject %s\n", p->subject);
 235                 if (p->seen) {
 236                         pr_warn("Sig %u: X.509 chain contains loop\n",
 237                                 sinfo->index);
 238                         return 0;
 239                 }
 240                 ret = x509_check_signature(p->pub, x509);
 241                 if (ret < 0)
 242                         return ret;
 243                 x509->signer = p;
 244                 if (x509 == p) {
 245                         pr_debug("- self-signed\n");
 246                         return 0;
 247                 }
 248                 x509 = p;
 249                 might_sleep();
 250         }
 251
 252 maybe_missing_crypto_in_x509:
 253         /* Just prune the certificate chain at this point if we lack some
 254          * crypto module to go further.  Note, however, we don't want to set
 255          * sinfo->missing_crypto as the signed info block may still be
 256          * validatable against an X.509 cert lower in the chain that we have a
 257          * trusted copy of.
 258          */
 259         if (ret == -ENOPKG)
 260                 return 0;
 261         return ret;
 262 }
 263
 264 /*
 265  * Verify one signed information block from a PKCS#7 message.
 266  */
 267 static int pkcs7_verify_one(struct pkcs7_message *pkcs7,
 268                             struct pkcs7_signed_info *sinfo)
 269 {
 270         int ret;
 271
 272         kenter(",%u", sinfo->index);
 273
 274         /* First of all, digest the data in the PKCS#7 message and the
 275          * signed information block
 276          */
 277         ret = pkcs7_digest(pkcs7, sinfo);
 278         if (ret < 0)
 279                 return ret;
 280
 281         /* Find the key for the signature if there is one */
 282         ret = pkcs7_find_key(pkcs7, sinfo);
 283         if (ret < 0)
 284                 return ret;
 285
 286         if (!sinfo->signer)
 287                 return 0;
 288
 289         pr_devel("Using X.509[%u] for sig %u\n",
 290                  sinfo->signer->index, sinfo->index);
 291
 292         /* Verify the PKCS#7 binary against the key */
 293         ret = public_key_verify_signature(sinfo->signer->pub, &sinfo->sig);
 294         if (ret < 0)
 295                 return ret;
 296
 297         pr_devel("Verified signature %u\n", sinfo->index);
 298
 299         /* Verify the internal certificate chain */
 300         return pkcs7_verify_sig_chain(pkcs7, sinfo);
 301 }
 302
 303 /**
 304  * pkcs7_verify - Verify a PKCS#7 message
 305  * @pkcs7: The PKCS#7 message to be verified
 306  *
 307  * Verify a PKCS#7 message is internally consistent - that is, the data digest
 308  * matches the digest in the AuthAttrs and any signature in the message or one
 309  * of the X.509 certificates it carries that matches another X.509 cert in the
 310  * message can be verified.
 311  *
 312  * This does not look to match the contents of the PKCS#7 message against any
 313  * external public keys.
 314  *
 315  * Returns, in order of descending priority:
 316  *
 317  *  (*) -EKEYREJECTED if a signature failed to match for which we found an
 318  *      appropriate X.509 certificate, or:
 319  *
 320  *  (*) -EBADMSG if some part of the message was invalid, or:
 321  *
 322  *  (*) -ENOPKG if none of the signature chains are verifiable because suitable
 323  *      crypto modules couldn't be found, or:
 324  *
 325  *  (*) 0 if all the signature chains that don't incur -ENOPKG can be verified
 326  *      (note that a signature chain may be of zero length), or:
 327  */
 328 int pkcs7_verify(struct pkcs7_message *pkcs7)
 329 {
 330         struct pkcs7_signed_info *sinfo;
 331         struct x509_certificate *x509;
 332         int enopkg = -ENOPKG;
 333         int ret, n;
 334
 335         kenter("");
 336
 337         for (n = 0, x509 = pkcs7->certs; x509; x509 = x509->next, n++) {
 338                 ret = x509_get_sig_params(x509);
 339                 if (ret < 0)
 340                         return ret;
 341         }
 342
 343         for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
 344                 ret = pkcs7_verify_one(pkcs7, sinfo);
 345                 if (ret < 0) {
 346                         if (ret == -ENOPKG) {
 347                                 sinfo->unsupported_crypto = true;
 348                                 continue;
 349                         }
 350                         kleave(" = %d", ret);
 351                         return ret;
 352                 }
 353                 enopkg = 0;
 354         }
 355
 356         kleave(" = %d", enopkg);
 357         return enopkg;
 358 }
 359 EXPORT_SYMBOL_GPL(pkcs7_verify);