crypto/asymmetric_keys/pkcs7_trust.c

   1 /* Validate the trust chain of 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 <linux/key.h>
  19 #include <keys/asymmetric-type.h>
  20 #include "public_key.h"
  21 #include "pkcs7_parser.h"
  22
  23 /**
  24  * Check the trust on one PKCS#7 SignedInfo block.
  25  */
  26 static int pkcs7_validate_trust_one(struct pkcs7_message *pkcs7,
  27                                     struct pkcs7_signed_info *sinfo,
  28                                     struct key *trust_keyring)
  29 {
  30         struct public_key_signature *sig = &sinfo->sig;
  31         struct x509_certificate *x509, *last = NULL, *p;
  32         struct key *key;
  33         bool trusted;
  34         int ret;
  35
  36         kenter(",%u,", sinfo->index);
  37
  38         if (sinfo->unsupported_crypto) {
  39                 kleave(" = -ENOPKG [cached]");
  40                 return -ENOPKG;
  41         }
  42
  43         for (x509 = sinfo->signer; x509; x509 = x509->signer) {
  44                 if (x509->seen) {
  45                         if (x509->verified) {
  46                                 trusted = x509->trusted;
  47                                 goto verified;
  48                         }
  49                         kleave(" = -ENOKEY [cached]");
  50                         return -ENOKEY;
  51                 }
  52                 x509->seen = true;
  53
  54                 /* Look to see if this certificate is present in the trusted
  55                  * keys.
  56                  */
  57                 key = x509_request_asymmetric_key(trust_keyring,
  58                                                   x509->id, x509->skid,
  59                                                   false);
  60                 if (!IS_ERR(key)) {
  61                         /* One of the X.509 certificates in the PKCS#7 message
  62                          * is apparently the same as one we already trust.
  63                          * Verify that the trusted variant can also validate
  64                          * the signature on the descendant.
  65                          */
  66                         pr_devel("sinfo %u: Cert %u as key %x\n",
  67                                  sinfo->index, x509->index, key_serial(key));
  68                         goto matched;
  69                 }
  70                 if (key == ERR_PTR(-ENOMEM))
  71                         return -ENOMEM;
  72
  73                  /* Self-signed certificates form roots of their own, and if we
  74                   * don't know them, then we can't accept them.
  75                   */
  76                 if (x509->next == x509) {
  77                         kleave(" = -ENOKEY [unknown self-signed]");
  78                         return -ENOKEY;
  79                 }
  80
  81                 might_sleep();
  82                 last = x509;
  83                 sig = &last->sig;
  84         }
  85
  86         /* No match - see if the root certificate has a signer amongst the
  87          * trusted keys.
  88          */
  89         if (last && (last->akid_id || last->akid_skid)) {
  90                 key = x509_request_asymmetric_key(trust_keyring,
  91                                                   last->akid_id,
  92                                                   last->akid_skid,
  93                                                   false);
  94                 if (!IS_ERR(key)) {
  95                         x509 = last;
  96                         pr_devel("sinfo %u: Root cert %u signer is key %x\n",
  97                                  sinfo->index, x509->index, key_serial(key));
  98                         goto matched;
  99                 }
 100                 if (PTR_ERR(key) != -ENOKEY)
 101                         return PTR_ERR(key);
 102         }
 103
 104         /* As a last resort, see if we have a trusted public key that matches
 105          * the signed info directly.
 106          */
 107         key = x509_request_asymmetric_key(trust_keyring,
 108                                           sinfo->signing_cert_id,
 109                                           NULL,
 110                                           false);
 111         if (!IS_ERR(key)) {
 112                 pr_devel("sinfo %u: Direct signer is key %x\n",
 113                          sinfo->index, key_serial(key));
 114                 x509 = NULL;
 115                 goto matched;
 116         }
 117         if (PTR_ERR(key) != -ENOKEY)
 118                 return PTR_ERR(key);
 119
 120         kleave(" = -ENOKEY [no backref]");
 121         return -ENOKEY;
 122
 123 matched:
 124         ret = verify_signature(key, sig);
 125         trusted = test_bit(KEY_FLAG_TRUSTED, &key->flags);
 126         key_put(key);
 127         if (ret < 0) {
 128                 if (ret == -ENOMEM)
 129                         return ret;
 130                 kleave(" = -EKEYREJECTED [verify %d]", ret);
 131                 return -EKEYREJECTED;
 132         }
 133
 134 verified:
 135         if (x509) {
 136                 x509->verified = true;
 137                 for (p = sinfo->signer; p != x509; p = p->signer) {
 138                         p->verified = true;
 139                         p->trusted = trusted;
 140                 }
 141         }
 142         sinfo->trusted = trusted;
 143         kleave(" = 0");
 144         return 0;
 145 }
 146
 147 /**
 148  * pkcs7_validate_trust - Validate PKCS#7 trust chain
 149  * @pkcs7: The PKCS#7 certificate to validate
 150  * @trust_keyring: Signing certificates to use as starting points
 151  * @_trusted: Set to true if trustworth, false otherwise
 152  *
 153  * Validate that the certificate chain inside the PKCS#7 message intersects
 154  * keys we already know and trust.
 155  *
 156  * Returns, in order of descending priority:
 157  *
 158  *  (*) -EKEYREJECTED if a signature failed to match for which we have a valid
 159  *      key, or:
 160  *
 161  *  (*) 0 if at least one signature chain intersects with the keys in the trust
 162  *      keyring, or:
 163  *
 164  *  (*) -ENOPKG if a suitable crypto module couldn't be found for a check on a
 165  *      chain.
 166  *
 167  *  (*) -ENOKEY if we couldn't find a match for any of the signature chains in
 168  *      the message.
 169  *
 170  * May also return -ENOMEM.
 171  */
 172 int pkcs7_validate_trust(struct pkcs7_message *pkcs7,
 173                          struct key *trust_keyring,
 174                          bool *_trusted)
 175 {
 176         struct pkcs7_signed_info *sinfo;
 177         struct x509_certificate *p;
 178         int cached_ret = -ENOKEY;
 179         int ret;
 180
 181         for (p = pkcs7->certs; p; p = p->next)
 182                 p->seen = false;
 183
 184         for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
 185                 ret = pkcs7_validate_trust_one(pkcs7, sinfo, trust_keyring);
 186                 switch (ret) {
 187                 case -ENOKEY:
 188                         continue;
 189                 case -ENOPKG:
 190                         if (cached_ret == -ENOKEY)
 191                                 cached_ret = -ENOPKG;
 192                         continue;
 193                 case 0:
 194                         *_trusted |= sinfo->trusted;
 195                         cached_ret = 0;
 196                         continue;
 197                 default:
 198                         return ret;
 199                 }
 200         }
 201
 202         return cached_ret;
 203 }
 204 EXPORT_SYMBOL_GPL(pkcs7_validate_trust);