crypto/asymmetric_keys/x509_public_key.c

   1 /* Instantiate a public key crypto key from an X.509 Certificate
   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) "X.509: "fmt
  13 #include <linux/module.h>
  14 #include <linux/kernel.h>
  15 #include <linux/slab.h>
  16 #include <linux/err.h>
  17 #include <linux/mpi.h>
  18 #include <linux/asn1_decoder.h>
  19 #include <keys/asymmetric-subtype.h>
  20 #include <keys/asymmetric-parser.h>
  21 #include <keys/system_keyring.h>
  22 #include <crypto/hash.h>
  23 #include "asymmetric_keys.h"
  24 #include "public_key.h"
  25 #include "x509_parser.h"
  26
  27 static bool use_builtin_keys;
  28 static char *ca_keyid;
  29
  30 #ifndef MODULE
  31 static int __init ca_keys_setup(char *str)
  32 {
  33         if (!str)               /* default system keyring */
  34                 return 1;
  35
  36         if (strncmp(str, "id:", 3) == 0)
  37                 ca_keyid = str; /* owner key 'id:xxxxxx' */
  38         else if (strcmp(str, "builtin") == 0)
  39                 use_builtin_keys = true;
  40
  41         return 1;
  42 }
  43 __setup("ca_keys=", ca_keys_setup);
  44 #endif
  45
  46 /**
  47  * x509_request_asymmetric_key - Request a key by X.509 certificate params.
  48  * @keyring: The keys to search.
  49  * @subject: The name of the subject to whom the key belongs.
  50  * @key_id: The subject key ID as a hex string.
  51  *
  52  * Find a key in the given keyring by subject name and key ID.  These might,
  53  * for instance, be the issuer name and the authority key ID of an X.509
  54  * certificate that needs to be verified.
  55  */
  56 struct key *x509_request_asymmetric_key(struct key *keyring,
  57                                         const char *subject,
  58                                         const char *key_id)
  59 {
  60         key_ref_t key;
  61         size_t subject_len = strlen(subject), key_id_len = strlen(key_id);
  62         char *id;
  63
  64         /* Construct an identifier "<subjname>:<keyid>". */
  65         id = kmalloc(subject_len + 2 + key_id_len + 1, GFP_KERNEL);
  66         if (!id)
  67                 return ERR_PTR(-ENOMEM);
  68
  69         memcpy(id, subject, subject_len);
  70         id[subject_len + 0] = ':';
  71         id[subject_len + 1] = ' ';
  72         memcpy(id + subject_len + 2, key_id, key_id_len);
  73         id[subject_len + 2 + key_id_len] = 0;
  74
  75         pr_debug("Look up: \"%s\"\n", id);
  76
  77         key = keyring_search(make_key_ref(keyring, 1),
  78                              &key_type_asymmetric, id);
  79         if (IS_ERR(key))
  80                 pr_debug("Request for key '%s' err %ld\n", id, PTR_ERR(key));
  81         kfree(id);
  82
  83         if (IS_ERR(key)) {
  84                 switch (PTR_ERR(key)) {
  85                         /* Hide some search errors */
  86                 case -EACCES:
  87                 case -ENOTDIR:
  88                 case -EAGAIN:
  89                         return ERR_PTR(-ENOKEY);
  90                 default:
  91                         return ERR_CAST(key);
  92                 }
  93         }
  94
  95         pr_devel("<==%s() = 0 [%x]\n", __func__,
  96                  key_serial(key_ref_to_ptr(key)));
  97         return key_ref_to_ptr(key);
  98 }
  99 EXPORT_SYMBOL_GPL(x509_request_asymmetric_key);
 100
 101 /*
 102  * Set up the signature parameters in an X.509 certificate.  This involves
 103  * digesting the signed data and extracting the signature.
 104  */
 105 int x509_get_sig_params(struct x509_certificate *cert)
 106 {
 107         struct crypto_shash *tfm;
 108         struct shash_desc *desc;
 109         size_t digest_size, desc_size;
 110         void *digest;
 111         int ret;
 112
 113         pr_devel("==>%s()\n", __func__);
 114
 115         if (cert->sig.rsa.s)
 116                 return 0;
 117
 118         cert->sig.rsa.s = mpi_read_raw_data(cert->raw_sig, cert->raw_sig_size);
 119         if (!cert->sig.rsa.s)
 120                 return -ENOMEM;
 121         cert->sig.nr_mpi = 1;
 122
 123         /* Allocate the hashing algorithm we're going to need and find out how
 124          * big the hash operational data will be.
 125          */
 126         tfm = crypto_alloc_shash(hash_algo_name[cert->sig.pkey_hash_algo], 0, 0);
 127         if (IS_ERR(tfm))
 128                 return (PTR_ERR(tfm) == -ENOENT) ? -ENOPKG : PTR_ERR(tfm);
 129
 130         desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
 131         digest_size = crypto_shash_digestsize(tfm);
 132
 133         /* We allocate the hash operational data storage on the end of the
 134          * digest storage space.
 135          */
 136         ret = -ENOMEM;
 137         digest = kzalloc(digest_size + desc_size, GFP_KERNEL);
 138         if (!digest)
 139                 goto error;
 140
 141         cert->sig.digest = digest;
 142         cert->sig.digest_size = digest_size;
 143
 144         desc = digest + digest_size;
 145         desc->tfm = tfm;
 146         desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
 147
 148         ret = crypto_shash_init(desc);
 149         if (ret < 0)
 150                 goto error;
 151         might_sleep();
 152         ret = crypto_shash_finup(desc, cert->tbs, cert->tbs_size, digest);
 153 error:
 154         crypto_free_shash(tfm);
 155         pr_devel("<==%s() = %d\n", __func__, ret);
 156         return ret;
 157 }
 158 EXPORT_SYMBOL_GPL(x509_get_sig_params);
 159
 160 /*
 161  * Check the signature on a certificate using the provided public key
 162  */
 163 int x509_check_signature(const struct public_key *pub,
 164                          struct x509_certificate *cert)
 165 {
 166         int ret;
 167
 168         pr_devel("==>%s()\n", __func__);
 169
 170         ret = x509_get_sig_params(cert);
 171         if (ret < 0)
 172                 return ret;
 173
 174         ret = public_key_verify_signature(pub, &cert->sig);
 175         pr_debug("Cert Verification: %d\n", ret);
 176         return ret;
 177 }
 178 EXPORT_SYMBOL_GPL(x509_check_signature);
 179
 180 /*
 181  * Check the new certificate against the ones in the trust keyring.  If one of
 182  * those is the signing key and validates the new certificate, then mark the
 183  * new certificate as being trusted.
 184  *
 185  * Return 0 if the new certificate was successfully validated, 1 if we couldn't
 186  * find a matching parent certificate in the trusted list and an error if there
 187  * is a matching certificate but the signature check fails.
 188  */
 189 static int x509_validate_trust(struct x509_certificate *cert,
 190                                struct key *trust_keyring)
 191 {
 192         struct key *key;
 193         int ret = 1;
 194
 195         if (!trust_keyring)
 196                 return -EOPNOTSUPP;
 197
 198         if (ca_keyid && !asymmetric_keyid_match(cert->authority, ca_keyid))
 199                 return -EPERM;
 200
 201         key = x509_request_asymmetric_key(trust_keyring,
 202                                           cert->issuer, cert->authority);
 203         if (!IS_ERR(key))  {
 204                 if (!use_builtin_keys
 205                     || test_bit(KEY_FLAG_BUILTIN, &key->flags))
 206                         ret = x509_check_signature(key->payload.data, cert);
 207                 key_put(key);
 208         }
 209         return ret;
 210 }
 211
 212 /*
 213  * Attempt to parse a data blob for a key as an X509 certificate.
 214  */
 215 static int x509_key_preparse(struct key_preparsed_payload *prep)
 216 {
 217         struct x509_certificate *cert;
 218         size_t srlen, sulen;
 219         char *desc = NULL;
 220         int ret;
 221
 222         cert = x509_cert_parse(prep->data, prep->datalen);
 223         if (IS_ERR(cert))
 224                 return PTR_ERR(cert);
 225
 226         pr_devel("Cert Issuer: %s\n", cert->issuer);
 227         pr_devel("Cert Subject: %s\n", cert->subject);
 228
 229         if (cert->pub->pkey_algo >= PKEY_ALGO__LAST ||
 230             cert->sig.pkey_algo >= PKEY_ALGO__LAST ||
 231             cert->sig.pkey_hash_algo >= PKEY_HASH__LAST ||
 232             !pkey_algo[cert->pub->pkey_algo] ||
 233             !pkey_algo[cert->sig.pkey_algo] ||
 234             !hash_algo_name[cert->sig.pkey_hash_algo]) {
 235                 ret = -ENOPKG;
 236                 goto error_free_cert;
 237         }
 238
 239         pr_devel("Cert Key Algo: %s\n", pkey_algo_name[cert->pub->pkey_algo]);
 240         pr_devel("Cert Valid From: %04ld-%02d-%02d %02d:%02d:%02d\n",
 241                  cert->valid_from.tm_year + 1900, cert->valid_from.tm_mon + 1,
 242                  cert->valid_from.tm_mday, cert->valid_from.tm_hour,
 243                  cert->valid_from.tm_min,  cert->valid_from.tm_sec);
 244         pr_devel("Cert Valid To: %04ld-%02d-%02d %02d:%02d:%02d\n",
 245                  cert->valid_to.tm_year + 1900, cert->valid_to.tm_mon + 1,
 246                  cert->valid_to.tm_mday, cert->valid_to.tm_hour,
 247                  cert->valid_to.tm_min,  cert->valid_to.tm_sec);
 248         pr_devel("Cert Signature: %s + %s\n",
 249                  pkey_algo_name[cert->sig.pkey_algo],
 250                  hash_algo_name[cert->sig.pkey_hash_algo]);
 251
 252         if (!cert->fingerprint) {
 253                 pr_warn("Cert for '%s' must have a SubjKeyId extension\n",
 254                         cert->subject);
 255                 ret = -EKEYREJECTED;
 256                 goto error_free_cert;
 257         }
 258
 259         cert->pub->algo = pkey_algo[cert->pub->pkey_algo];
 260         cert->pub->id_type = PKEY_ID_X509;
 261
 262         /* Check the signature on the key if it appears to be self-signed */
 263         if (!cert->authority ||
 264             strcmp(cert->fingerprint, cert->authority) == 0) {
 265                 ret = x509_check_signature(cert->pub, cert); /* self-signed */
 266                 if (ret < 0)
 267                         goto error_free_cert;
 268         } else if (!prep->trusted) {
 269                 ret = x509_validate_trust(cert, get_system_trusted_keyring());
 270                 if (!ret)
 271                         prep->trusted = 1;
 272         }
 273
 274         /* Propose a description */
 275         sulen = strlen(cert->subject);
 276         srlen = strlen(cert->fingerprint);
 277         ret = -ENOMEM;
 278         desc = kmalloc(sulen + 2 + srlen + 1, GFP_KERNEL);
 279         if (!desc)
 280                 goto error_free_cert;
 281         memcpy(desc, cert->subject, sulen);
 282         desc[sulen] = ':';
 283         desc[sulen + 1] = ' ';
 284         memcpy(desc + sulen + 2, cert->fingerprint, srlen);
 285         desc[sulen + 2 + srlen] = 0;
 286
 287         /* We're pinning the module by being linked against it */
 288         __module_get(public_key_subtype.owner);
 289         prep->type_data[0] = &public_key_subtype;
 290         prep->type_data[1] = cert->fingerprint;
 291         prep->payload[0] = cert->pub;
 292         prep->description = desc;
 293         prep->quotalen = 100;
 294
 295         /* We've finished with the certificate */
 296         cert->pub = NULL;
 297         cert->fingerprint = NULL;
 298         desc = NULL;
 299         ret = 0;
 300
 301 error_free_cert:
 302         x509_free_certificate(cert);
 303         return ret;
 304 }
 305
 306 static struct asymmetric_key_parser x509_key_parser = {
 307         .owner  = THIS_MODULE,
 308         .name   = "x509",
 309         .parse  = x509_key_preparse,
 310 };
 311
 312 /*
 313  * Module stuff
 314  */
 315 static int __init x509_key_init(void)
 316 {
 317         return register_asymmetric_key_parser(&x509_key_parser);
 318 }
 319
 320 static void __exit x509_key_exit(void)
 321 {
 322         unregister_asymmetric_key_parser(&x509_key_parser);
 323 }
 324
 325 module_init(x509_key_init);
 326 module_exit(x509_key_exit);
 327
 328 MODULE_DESCRIPTION("X.509 certificate parser");
 329 MODULE_LICENSE("GPL");