crypto/asymmetric_keys/pkcs7_trust.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /* Validate the trust chain of 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 <linux/key.h>
  15 #include <keys/asymmetric-type.h>
  16 #include <crypto/public_key.h>
  17 #include "pkcs7_parser.h"
  18
  19 /*
  20  * Check the trust on one PKCS#7 SignedInfo block.
  21  */
  22 static int pkcs7_validate_trust_one(struct pkcs7_message *pkcs7,
  23                                     struct pkcs7_signed_info *sinfo,
  24                                     struct key *trust_keyring)
  25 {
  26         struct public_key_signature *sig = sinfo->sig;
  27         struct x509_certificate *x509, *last = NULL, *p;
  28         struct key *key;
  29         int ret;
  30
  31         kenter(",%u,", sinfo->index);
  32
  33         if (sinfo->unsupported_crypto) {
  34                 kleave(" = -ENOPKG [cached]");
  35                 return -ENOPKG;
  36         }
  37
  38         for (x509 = sinfo->signer; x509; x509 = x509->signer) {
  39                 if (x509->seen) {
  40                         if (x509->verified)
  41                                 goto verified;
  42                         kleave(" = -ENOKEY [cached]");
  43                         return -ENOKEY;
  44                 }
  45                 x509->seen = true;
  46
  47                 /* Look to see if this certificate is present in the trusted
  48                  * keys.
  49                  */
  50                 key = find_asymmetric_key(trust_keyring,
  51                                           x509->id, x509->skid, false);
  52                 if (!IS_ERR(key)) {
  53                         /* One of the X.509 certificates in the PKCS#7 message
  54                          * is apparently the same as one we already trust.
  55                          * Verify that the trusted variant can also validate
  56                          * the signature on the descendant.
  57                          */
  58                         pr_devel("sinfo %u: Cert %u as key %x\n",
  59                                  sinfo->index, x509->index, key_serial(key));
  60                         goto matched;
  61                 }
  62                 if (key == ERR_PTR(-ENOMEM))
  63                         return -ENOMEM;
  64
  65                  /* Self-signed certificates form roots of their own, and if we
  66                   * don't know them, then we can't accept them.
  67                   */
  68                 if (x509->signer == x509) {
  69                         kleave(" = -ENOKEY [unknown self-signed]");
  70                         return -ENOKEY;
  71                 }
  72
  73                 might_sleep();
  74                 last = x509;
  75                 sig = last->sig;
  76         }
  77
  78         /* No match - see if the root certificate has a signer amongst the
  79          * trusted keys.
  80          */
  81         if (last && (last->sig->auth_ids[0] || last->sig->auth_ids[1])) {
  82                 key = find_asymmetric_key(trust_keyring,
  83                                           last->sig->auth_ids[0],
  84                                           last->sig->auth_ids[1],
  85                                           false);
  86                 if (!IS_ERR(key)) {
  87                         x509 = last;
  88                         pr_devel("sinfo %u: Root cert %u signer is key %x\n",
  89                                  sinfo->index, x509->index, key_serial(key));
  90                         goto matched;
  91                 }
  92                 if (PTR_ERR(key) != -ENOKEY)
  93                         return PTR_ERR(key);
  94         }
  95
  96         /* As a last resort, see if we have a trusted public key that matches
  97          * the signed info directly.
  98          */
  99         key = find_asymmetric_key(trust_keyring,
 100                                   sinfo->sig->auth_ids[0], NULL, false);
 101         if (!IS_ERR(key)) {
 102                 pr_devel("sinfo %u: Direct signer is key %x\n",
 103                          sinfo->index, key_serial(key));
 104                 x509 = NULL;
 105                 sig = sinfo->sig;
 106                 goto matched;
 107         }
 108         if (PTR_ERR(key) != -ENOKEY)
 109                 return PTR_ERR(key);
 110
 111         kleave(" = -ENOKEY [no backref]");
 112         return -ENOKEY;
 113
 114 matched:
 115         ret = verify_signature(key, sig);
 116         key_put(key);
 117         if (ret < 0) {
 118                 if (ret == -ENOMEM)
 119                         return ret;
 120                 kleave(" = -EKEYREJECTED [verify %d]", ret);
 121                 return -EKEYREJECTED;
 122         }
 123
 124 verified:
 125         if (x509) {
 126                 x509->verified = true;
 127                 for (p = sinfo->signer; p != x509; p = p->signer)
 128                         p->verified = true;
 129         }
 130         kleave(" = 0");
 131         return 0;
 132 }
 133
 134 /**
 135  * pkcs7_validate_trust - Validate PKCS#7 trust chain
 136  * @pkcs7: The PKCS#7 certificate to validate
 137  * @trust_keyring: Signing certificates to use as starting points
 138  *
 139  * Validate that the certificate chain inside the PKCS#7 message intersects
 140  * keys we already know and trust.
 141  *
 142  * Returns, in order of descending priority:
 143  *
 144  *  (*) -EKEYREJECTED if a signature failed to match for which we have a valid
 145  *      key, or:
 146  *
 147  *  (*) 0 if at least one signature chain intersects with the keys in the trust
 148  *      keyring, or:
 149  *
 150  *  (*) -ENOPKG if a suitable crypto module couldn't be found for a check on a
 151  *      chain.
 152  *
 153  *  (*) -ENOKEY if we couldn't find a match for any of the signature chains in
 154  *      the message.
 155  *
 156  * May also return -ENOMEM.
 157  */
 158 int pkcs7_validate_trust(struct pkcs7_message *pkcs7,
 159                          struct key *trust_keyring)
 160 {
 161         struct pkcs7_signed_info *sinfo;
 162         struct x509_certificate *p;
 163         int cached_ret = -ENOKEY;
 164         int ret;
 165
 166         for (p = pkcs7->certs; p; p = p->next)
 167                 p->seen = false;
 168
 169         for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
 170                 ret = pkcs7_validate_trust_one(pkcs7, sinfo, trust_keyring);
 171                 switch (ret) {
 172                 case -ENOKEY:
 173                         continue;
 174                 case -ENOPKG:
 175                         if (cached_ret == -ENOKEY)
 176                                 cached_ret = -ENOPKG;
 177                         continue;
 178                 case 0:
 179                         cached_ret = 0;
 180                         continue;
 181                 default:
 182                         return ret;
 183                 }
 184         }
 185
 186         return cached_ret;
 187 }
 188 EXPORT_SYMBOL_GPL(pkcs7_validate_trust);