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 struct asymmetric_key_id *ca_keyid;
  29
  30 #ifndef MODULE
  31 static struct {
  32         struct asymmetric_key_id id;
  33         unsigned char data[10];
  34 } cakey;
  35
  36 static int __init ca_keys_setup(char *str)
  37 {
  38         if (!str)               /* default system keyring */
  39                 return 1;
  40
  41         if (strncmp(str, "id:", 3) == 0) {
  42                 struct asymmetric_key_id *p = &cakey.id;
  43                 size_t hexlen = (strlen(str) - 3) / 2;
  44                 int ret;
  45
  46                 if (hexlen == 0 || hexlen > sizeof(cakey.data)) {
  47                         pr_err("Missing or invalid ca_keys id\n");
  48                         return 1;
  49                 }
  50
  51                 ret = __asymmetric_key_hex_to_key_id(str + 3, p, hexlen);
  52                 if (ret < 0)
  53                         pr_err("Unparsable ca_keys id hex string\n");
  54                 else
  55                         ca_keyid = p;   /* owner key 'id:xxxxxx' */
  56         } else if (strcmp(str, "builtin") == 0) {
  57                 use_builtin_keys = true;
  58         }
  59
  60         return 1;
  61 }
  62 __setup("ca_keys=", ca_keys_setup);
  63 #endif
  64
  65 /**
  66  * x509_request_asymmetric_key - Request a key by X.509 certificate params.
  67  * @keyring: The keys to search.
  68  * @kid: The key ID.
  69  * @partial: Use partial match if true, exact if false.
  70  *
  71  * Find a key in the given keyring by subject name and key ID.  These might,
  72  * for instance, be the issuer name and the authority key ID of an X.509
  73  * certificate that needs to be verified.
  74  */
  75 struct key *x509_request_asymmetric_key(struct key *keyring,
  76                                         const struct asymmetric_key_id *kid,
  77                                         bool partial)
  78 {
  79         key_ref_t key;
  80         char *id, *p;
  81
  82         /* Construct an identifier "id:<keyid>". */
  83         p = id = kmalloc(2 + 1 + kid->len * 2 + 1, GFP_KERNEL);
  84         if (!id)
  85                 return ERR_PTR(-ENOMEM);
  86
  87         if (partial) {
  88                 *p++ = 'i';
  89                 *p++ = 'd';
  90         } else {
  91                 *p++ = 'e';
  92                 *p++ = 'x';
  93         }
  94         *p++ = ':';
  95         p = bin2hex(p, kid->data, kid->len);
  96         *p = 0;
  97
  98         pr_debug("Look up: \"%s\"\n", id);
  99
 100         key = keyring_search(make_key_ref(keyring, 1),
 101                              &key_type_asymmetric, id);
 102         if (IS_ERR(key))
 103                 pr_debug("Request for key '%s' err %ld\n", id, PTR_ERR(key));
 104         kfree(id);
 105
 106         if (IS_ERR(key)) {
 107                 switch (PTR_ERR(key)) {
 108                         /* Hide some search errors */
 109                 case -EACCES:
 110                 case -ENOTDIR:
 111                 case -EAGAIN:
 112                         return ERR_PTR(-ENOKEY);
 113                 default:
 114                         return ERR_CAST(key);
 115                 }
 116         }
 117
 118         pr_devel("<==%s() = 0 [%x]\n", __func__,
 119                  key_serial(key_ref_to_ptr(key)));
 120         return key_ref_to_ptr(key);
 121 }
 122 EXPORT_SYMBOL_GPL(x509_request_asymmetric_key);
 123
 124 /*
 125  * Set up the signature parameters in an X.509 certificate.  This involves
 126  * digesting the signed data and extracting the signature.
 127  */
 128 int x509_get_sig_params(struct x509_certificate *cert)
 129 {
 130         struct crypto_shash *tfm;
 131         struct shash_desc *desc;
 132         size_t digest_size, desc_size;
 133         void *digest;
 134         int ret;
 135
 136         pr_devel("==>%s()\n", __func__);
 137
 138         if (cert->unsupported_crypto)
 139                 return -ENOPKG;
 140         if (cert->sig.rsa.s)
 141                 return 0;
 142
 143         cert->sig.rsa.s = mpi_read_raw_data(cert->raw_sig, cert->raw_sig_size);
 144         if (!cert->sig.rsa.s)
 145                 return -ENOMEM;
 146         cert->sig.nr_mpi = 1;
 147
 148         /* Allocate the hashing algorithm we're going to need and find out how
 149          * big the hash operational data will be.
 150          */
 151         tfm = crypto_alloc_shash(hash_algo_name[cert->sig.pkey_hash_algo], 0, 0);
 152         if (IS_ERR(tfm)) {
 153                 if (PTR_ERR(tfm) == -ENOENT) {
 154                         cert->unsupported_crypto = true;
 155                         return -ENOPKG;
 156                 }
 157                 return PTR_ERR(tfm);
 158         }
 159
 160         desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
 161         digest_size = crypto_shash_digestsize(tfm);
 162
 163         /* We allocate the hash operational data storage on the end of the
 164          * digest storage space.
 165          */
 166         ret = -ENOMEM;
 167         digest = kzalloc(digest_size + desc_size, GFP_KERNEL);
 168         if (!digest)
 169                 goto error;
 170
 171         cert->sig.digest = digest;
 172         cert->sig.digest_size = digest_size;
 173
 174         desc = digest + digest_size;
 175         desc->tfm = tfm;
 176         desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
 177
 178         ret = crypto_shash_init(desc);
 179         if (ret < 0)
 180                 goto error;
 181         might_sleep();
 182         ret = crypto_shash_finup(desc, cert->tbs, cert->tbs_size, digest);
 183 error:
 184         crypto_free_shash(tfm);
 185         pr_devel("<==%s() = %d\n", __func__, ret);
 186         return ret;
 187 }
 188 EXPORT_SYMBOL_GPL(x509_get_sig_params);
 189
 190 /*
 191  * Check the signature on a certificate using the provided public key
 192  */
 193 int x509_check_signature(const struct public_key *pub,
 194                          struct x509_certificate *cert)
 195 {
 196         int ret;
 197
 198         pr_devel("==>%s()\n", __func__);
 199
 200         ret = x509_get_sig_params(cert);
 201         if (ret < 0)
 202                 return ret;
 203
 204         ret = public_key_verify_signature(pub, &cert->sig);
 205         if (ret == -ENOPKG)
 206                 cert->unsupported_crypto = true;
 207         pr_debug("Cert Verification: %d\n", ret);
 208         return ret;
 209 }
 210 EXPORT_SYMBOL_GPL(x509_check_signature);
 211
 212 /*
 213  * Check the new certificate against the ones in the trust keyring.  If one of
 214  * those is the signing key and validates the new certificate, then mark the
 215  * new certificate as being trusted.
 216  *
 217  * Return 0 if the new certificate was successfully validated, 1 if we couldn't
 218  * find a matching parent certificate in the trusted list and an error if there
 219  * is a matching certificate but the signature check fails.
 220  */
 221 static int x509_validate_trust(struct x509_certificate *cert,
 222                                struct key *trust_keyring)
 223 {
 224         struct key *key;
 225         int ret = 1;
 226
 227         if (!trust_keyring)
 228                 return -EOPNOTSUPP;
 229
 230         if (ca_keyid && !asymmetric_key_id_partial(cert->akid_skid, ca_keyid))
 231                 return -EPERM;
 232
 233         key = x509_request_asymmetric_key(trust_keyring, cert->akid_skid,
 234                                           false);
 235         if (!IS_ERR(key))  {
 236                 if (!use_builtin_keys
 237                     || test_bit(KEY_FLAG_BUILTIN, &key->flags))
 238                         ret = x509_check_signature(key->payload.data, cert);
 239                 key_put(key);
 240         }
 241         return ret;
 242 }
 243
 244 /*
 245  * Attempt to parse a data blob for a key as an X509 certificate.
 246  */
 247 static int x509_key_preparse(struct key_preparsed_payload *prep)
 248 {
 249         struct asymmetric_key_ids *kids;
 250         struct x509_certificate *cert;
 251         const char *q;
 252         size_t srlen, sulen;
 253         char *desc = NULL, *p;
 254         int ret;
 255
 256         cert = x509_cert_parse(prep->data, prep->datalen);
 257         if (IS_ERR(cert))
 258                 return PTR_ERR(cert);
 259
 260         pr_devel("Cert Issuer: %s\n", cert->issuer);
 261         pr_devel("Cert Subject: %s\n", cert->subject);
 262
 263         if (cert->pub->pkey_algo >= PKEY_ALGO__LAST ||
 264             cert->sig.pkey_algo >= PKEY_ALGO__LAST ||
 265             cert->sig.pkey_hash_algo >= PKEY_HASH__LAST ||
 266             !pkey_algo[cert->pub->pkey_algo] ||
 267             !pkey_algo[cert->sig.pkey_algo] ||
 268             !hash_algo_name[cert->sig.pkey_hash_algo]) {
 269                 ret = -ENOPKG;
 270                 goto error_free_cert;
 271         }
 272
 273         pr_devel("Cert Key Algo: %s\n", pkey_algo_name[cert->pub->pkey_algo]);
 274         pr_devel("Cert Valid period: %lld-%lld\n", cert->valid_from, cert->valid_to);
 275         pr_devel("Cert Signature: %s + %s\n",
 276                  pkey_algo_name[cert->sig.pkey_algo],
 277                  hash_algo_name[cert->sig.pkey_hash_algo]);
 278
 279         cert->pub->algo = pkey_algo[cert->pub->pkey_algo];
 280         cert->pub->id_type = PKEY_ID_X509;
 281
 282         /* Check the signature on the key if it appears to be self-signed */
 283         if (!cert->akid_skid ||
 284             asymmetric_key_id_same(cert->skid, cert->akid_skid)) {
 285                 ret = x509_check_signature(cert->pub, cert); /* self-signed */
 286                 if (ret < 0)
 287                         goto error_free_cert;
 288         } else if (!prep->trusted) {
 289                 ret = x509_validate_trust(cert, get_system_trusted_keyring());
 290                 if (!ret)
 291                         prep->trusted = 1;
 292         }
 293
 294         /* Propose a description */
 295         sulen = strlen(cert->subject);
 296         if (cert->raw_skid) {
 297                 srlen = cert->raw_skid_size;
 298                 q = cert->raw_skid;
 299         } else {
 300                 srlen = cert->raw_serial_size;
 301                 q = cert->raw_serial;
 302         }
 303
 304         ret = -ENOMEM;
 305         desc = kmalloc(sulen + 2 + srlen * 2 + 1, GFP_KERNEL);
 306         if (!desc)
 307                 goto error_free_cert;
 308         p = memcpy(desc, cert->subject, sulen);
 309         p += sulen;
 310         *p++ = ':';
 311         *p++ = ' ';
 312         p = bin2hex(p, q, srlen);
 313         *p = 0;
 314
 315         kids = kmalloc(sizeof(struct asymmetric_key_ids), GFP_KERNEL);
 316         if (!kids)
 317                 goto error_free_desc;
 318         kids->id[0] = cert->id;
 319         kids->id[1] = cert->skid;
 320
 321         /* We're pinning the module by being linked against it */
 322         __module_get(public_key_subtype.owner);
 323         prep->type_data[0] = &public_key_subtype;
 324         prep->type_data[1] = kids;
 325         prep->payload[0] = cert->pub;
 326         prep->description = desc;
 327         prep->quotalen = 100;
 328
 329         /* We've finished with the certificate */
 330         cert->pub = NULL;
 331         cert->id = NULL;
 332         cert->skid = NULL;
 333         desc = NULL;
 334         ret = 0;
 335
 336 error_free_desc:
 337         kfree(desc);
 338 error_free_cert:
 339         x509_free_certificate(cert);
 340         return ret;
 341 }
 342
 343 static struct asymmetric_key_parser x509_key_parser = {
 344         .owner  = THIS_MODULE,
 345         .name   = "x509",
 346         .parse  = x509_key_preparse,
 347 };
 348
 349 /*
 350  * Module stuff
 351  */
 352 static int __init x509_key_init(void)
 353 {
 354         return register_asymmetric_key_parser(&x509_key_parser);
 355 }
 356
 357 static void __exit x509_key_exit(void)
 358 {
 359         unregister_asymmetric_key_parser(&x509_key_parser);
 360 }
 361
 362 module_init(x509_key_init);
 363 module_exit(x509_key_exit);
 364
 365 MODULE_DESCRIPTION("X.509 certificate parser");
 366 MODULE_LICENSE("GPL");