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,%u,%u",
 135                sinfo->index, sinfo->raw_serial_size, sinfo->raw_issuer_size);
 136
 137         for (x509 = pkcs7->certs; x509; x509 = x509->next, certix++) {
 138                 /* I'm _assuming_ that the generator of the PKCS#7 message will
 139                  * encode the fields from the X.509 cert in the same way in the
 140                  * PKCS#7 message - but I can't be 100% sure of that.  It's
 141                  * possible this will need element-by-element comparison.
 142                  */
 143                 if (x509->raw_serial_size != sinfo->raw_serial_size ||
 144                     memcmp(x509->raw_serial, sinfo->raw_serial,
 145                            sinfo->raw_serial_size) != 0)
 146                         continue;
 147                 pr_devel("Sig %u: Found cert serial match X.509[%u]\n",
 148                          sinfo->index, certix);
 149
 150                 if (x509->raw_issuer_size != sinfo->raw_issuer_size ||
 151                     memcmp(x509->raw_issuer, sinfo->raw_issuer,
 152                            sinfo->raw_issuer_size) != 0) {
 153                         pr_warn("Sig %u: X.509 subject and PKCS#7 issuer don't match\n",
 154                                 sinfo->index);
 155                         continue;
 156                 }
 157
 158                 if (x509->pub->pkey_algo != sinfo->sig.pkey_algo) {
 159                         pr_warn("Sig %u: X.509 algo and PKCS#7 sig algo don't match\n",
 160                                 sinfo->index);
 161                         continue;
 162                 }
 163
 164                 sinfo->signer = x509;
 165                 return 0;
 166         }
 167         pr_warn("Sig %u: Issuing X.509 cert not found (#%*ph)\n",
 168                 sinfo->index, sinfo->raw_serial_size, sinfo->raw_serial);
 169         return -ENOKEY;
 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 x509_certificate *x509 = sinfo->signer, *p;
 179         int ret;
 180
 181         kenter("");
 182
 183         for (p = pkcs7->certs; p; p = p->next)
 184                 p->seen = false;
 185
 186         for (;;) {
 187                 pr_debug("verify %s: %s\n", x509->subject, x509->fingerprint);
 188                 x509->seen = true;
 189                 ret = x509_get_sig_params(x509);
 190                 if (ret < 0)
 191                         return ret;
 192
 193                 pr_debug("- issuer %s\n", x509->issuer);
 194                 if (x509->authority)
 195                         pr_debug("- authkeyid %s\n", x509->authority);
 196
 197                 if (!x509->authority ||
 198                     strcmp(x509->subject, x509->issuer) == 0) {
 199                         /* If there's no authority certificate specified, then
 200                          * the certificate must be self-signed and is the root
 201                          * of the chain.  Likewise if the cert is its own
 202                          * authority.
 203                          */
 204                         pr_debug("- no auth?\n");
 205                         if (x509->raw_subject_size != x509->raw_issuer_size ||
 206                             memcmp(x509->raw_subject, x509->raw_issuer,
 207                                    x509->raw_issuer_size) != 0)
 208                                 return 0;
 209
 210                         ret = x509_check_signature(x509->pub, x509);
 211                         if (ret < 0)
 212                                 return ret;
 213                         x509->signer = x509;
 214                         pr_debug("- self-signed\n");
 215                         return 0;
 216                 }
 217
 218                 /* Look through the X.509 certificates in the PKCS#7 message's
 219                  * list to see if the next one is there.
 220                  */
 221                 pr_debug("- want %s\n", x509->authority);
 222                 for (p = pkcs7->certs; p; p = p->next) {
 223                         pr_debug("- cmp [%u] %s\n", p->index, p->fingerprint);
 224                         if (p->raw_subject_size == x509->raw_issuer_size &&
 225                             strcmp(p->fingerprint, x509->authority) == 0 &&
 226                             memcmp(p->raw_subject, x509->raw_issuer,
 227                                    x509->raw_issuer_size) == 0)
 228                                 goto found_issuer;
 229                 }
 230
 231                 /* We didn't find the root of this chain */
 232                 pr_debug("- top\n");
 233                 return 0;
 234
 235         found_issuer:
 236                 pr_debug("- issuer %s\n", p->subject);
 237                 if (p->seen) {
 238                         pr_warn("Sig %u: X.509 chain contains loop\n",
 239                                 sinfo->index);
 240                         return 0;
 241                 }
 242                 ret = x509_check_signature(p->pub, x509);
 243                 if (ret < 0)
 244                         return ret;
 245                 x509->signer = p;
 246                 if (x509 == p) {
 247                         pr_debug("- self-signed\n");
 248                         return 0;
 249                 }
 250                 x509 = p;
 251                 might_sleep();
 252         }
 253 }
 254
 255 /*
 256  * Verify one signed information block from a PKCS#7 message.
 257  */
 258 static int pkcs7_verify_one(struct pkcs7_message *pkcs7,
 259                             struct pkcs7_signed_info *sinfo)
 260 {
 261         int ret;
 262
 263         kenter(",%u", sinfo->index);
 264
 265         /* First of all, digest the data in the PKCS#7 message and the
 266          * signed information block
 267          */
 268         ret = pkcs7_digest(pkcs7, sinfo);
 269         if (ret < 0)
 270                 return ret;
 271
 272         /* Find the key for the signature */
 273         ret = pkcs7_find_key(pkcs7, sinfo);
 274         if (ret < 0)
 275                 return ret;
 276
 277         pr_devel("Using X.509[%u] for sig %u\n",
 278                  sinfo->signer->index, sinfo->index);
 279
 280         /* Verify the PKCS#7 binary against the key */
 281         ret = public_key_verify_signature(sinfo->signer->pub, &sinfo->sig);
 282         if (ret < 0)
 283                 return ret;
 284
 285         pr_devel("Verified signature %u\n", sinfo->index);
 286
 287         /* Verify the internal certificate chain */
 288         return pkcs7_verify_sig_chain(pkcs7, sinfo);
 289 }
 290
 291 /**
 292  * pkcs7_verify - Verify a PKCS#7 message
 293  * @pkcs7: The PKCS#7 message to be verified
 294  */
 295 int pkcs7_verify(struct pkcs7_message *pkcs7)
 296 {
 297         struct pkcs7_signed_info *sinfo;
 298         struct x509_certificate *x509;
 299         int ret, n;
 300
 301         kenter("");
 302
 303         for (n = 0, x509 = pkcs7->certs; x509; x509 = x509->next, n++) {
 304                 ret = x509_get_sig_params(x509);
 305                 if (ret < 0)
 306                         return ret;
 307                 pr_debug("X.509[%u] %s\n", n, x509->authority);
 308         }
 309
 310         for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
 311                 ret = pkcs7_verify_one(pkcs7, sinfo);
 312                 if (ret < 0) {
 313                         kleave(" = %d", ret);
 314                         return ret;
 315                 }
 316         }
 317
 318         kleave(" = 0");
 319         return 0;
 320 }
 321 EXPORT_SYMBOL_GPL(pkcs7_verify);