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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 | /* Verify the signature on a PKCS#7 message.
*
* Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public Licence
* as published by the Free Software Foundation; either version
* 2 of the Licence, or (at your option) any later version.
*/
#define pr_fmt(fmt) "PKCS7: "fmt
#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/slab.h>
#include <linux/err.h>
#include <linux/asn1.h>
#include <crypto/hash.h>
#include "public_key.h"
#include "pkcs7_parser.h"
/*
* Digest the relevant parts of the PKCS#7 data
*/
static int pkcs7_digest(struct pkcs7_message *pkcs7,
struct pkcs7_signed_info *sinfo)
{
struct crypto_shash *tfm;
struct shash_desc *desc;
size_t digest_size, desc_size;
void *digest;
int ret;
kenter(",%u,%u", sinfo->index, sinfo->sig.pkey_hash_algo);
if (sinfo->sig.pkey_hash_algo >= PKEY_HASH__LAST ||
!hash_algo_name[sinfo->sig.pkey_hash_algo])
return -ENOPKG;
/* Allocate the hashing algorithm we're going to need and find out how
* big the hash operational data will be.
*/
tfm = crypto_alloc_shash(hash_algo_name[sinfo->sig.pkey_hash_algo],
0, 0);
if (IS_ERR(tfm))
return (PTR_ERR(tfm) == -ENOENT) ? -ENOPKG : PTR_ERR(tfm);
desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
sinfo->sig.digest_size = digest_size = crypto_shash_digestsize(tfm);
ret = -ENOMEM;
digest = kzalloc(digest_size + desc_size, GFP_KERNEL);
if (!digest)
goto error_no_desc;
desc = digest + digest_size;
desc->tfm = tfm;
desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
/* Digest the message [RFC2315 9.3] */
ret = crypto_shash_init(desc);
if (ret < 0)
goto error;
ret = crypto_shash_finup(desc, pkcs7->data, pkcs7->data_len, digest);
if (ret < 0)
goto error;
pr_devel("MsgDigest = [%*ph]\n", 8, digest);
/* However, if there are authenticated attributes, there must be a
* message digest attribute amongst them which corresponds to the
* digest we just calculated.
*/
if (sinfo->msgdigest) {
u8 tag;
if (sinfo->msgdigest_len != sinfo->sig.digest_size) {
pr_debug("Sig %u: Invalid digest size (%u)\n",
sinfo->index, sinfo->msgdigest_len);
ret = -EBADMSG;
goto error;
}
if (memcmp(digest, sinfo->msgdigest, sinfo->msgdigest_len) != 0) {
pr_debug("Sig %u: Message digest doesn't match\n",
sinfo->index);
ret = -EKEYREJECTED;
goto error;
}
/* We then calculate anew, using the authenticated attributes
* as the contents of the digest instead. Note that we need to
* convert the attributes from a CONT.0 into a SET before we
* hash it.
*/
memset(digest, 0, sinfo->sig.digest_size);
ret = crypto_shash_init(desc);
if (ret < 0)
goto error;
tag = ASN1_CONS_BIT | ASN1_SET;
ret = crypto_shash_update(desc, &tag, 1);
if (ret < 0)
goto error;
ret = crypto_shash_finup(desc, sinfo->authattrs,
sinfo->authattrs_len, digest);
if (ret < 0)
goto error;
pr_devel("AADigest = [%*ph]\n", 8, digest);
}
sinfo->sig.digest = digest;
digest = NULL;
error:
kfree(digest);
error_no_desc:
crypto_free_shash(tfm);
kleave(" = %d", ret);
return ret;
}
/*
* Find the key (X.509 certificate) to use to verify a PKCS#7 message. PKCS#7
* uses the issuer's name and the issuing certificate serial number for
* matching purposes. These must match the certificate issuer's name (not
* subject's name) and the certificate serial number [RFC 2315 6.7].
*/
static int pkcs7_find_key(struct pkcs7_message *pkcs7,
struct pkcs7_signed_info *sinfo)
{
struct x509_certificate *x509;
unsigned certix = 1;
kenter("%u", sinfo->index);
for (x509 = pkcs7->certs; x509; x509 = x509->next, certix++) {
/* I'm _assuming_ that the generator of the PKCS#7 message will
* encode the fields from the X.509 cert in the same way in the
* PKCS#7 message - but I can't be 100% sure of that. It's
* possible this will need element-by-element comparison.
*/
if (!asymmetric_key_id_same(x509->id, sinfo->signing_cert_id))
continue;
pr_devel("Sig %u: Found cert serial match X.509[%u]\n",
sinfo->index, certix);
if (x509->pub->pkey_algo != sinfo->sig.pkey_algo) {
pr_warn("Sig %u: X.509 algo and PKCS#7 sig algo don't match\n",
sinfo->index);
continue;
}
sinfo->signer = x509;
return 0;
}
/* The relevant X.509 cert isn't found here, but it might be found in
* the trust keyring.
*/
pr_debug("Sig %u: Issuing X.509 cert not found (#%*phN)\n",
sinfo->index,
sinfo->signing_cert_id->len, sinfo->signing_cert_id->data);
return 0;
}
/*
* Verify the internal certificate chain as best we can.
*/
static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7,
struct pkcs7_signed_info *sinfo)
{
struct x509_certificate *x509 = sinfo->signer, *p;
int ret;
kenter("");
for (p = pkcs7->certs; p; p = p->next)
p->seen = false;
for (;;) {
pr_debug("verify %s: %*phN\n",
x509->subject,
x509->raw_serial_size, x509->raw_serial);
x509->seen = true;
ret = x509_get_sig_params(x509);
if (ret < 0)
goto maybe_missing_crypto_in_x509;
pr_debug("- issuer %s\n", x509->issuer);
if (x509->akid_skid)
pr_debug("- authkeyid %*phN\n",
x509->akid_skid->len, x509->akid_skid->data);
if (!x509->akid_skid ||
strcmp(x509->subject, x509->issuer) == 0) {
/* If there's no authority certificate specified, then
* the certificate must be self-signed and is the root
* of the chain. Likewise if the cert is its own
* authority.
*/
pr_debug("- no auth?\n");
if (x509->raw_subject_size != x509->raw_issuer_size ||
memcmp(x509->raw_subject, x509->raw_issuer,
x509->raw_issuer_size) != 0)
return 0;
ret = x509_check_signature(x509->pub, x509);
if (ret < 0)
goto maybe_missing_crypto_in_x509;
x509->signer = x509;
pr_debug("- self-signed\n");
return 0;
}
/* Look through the X.509 certificates in the PKCS#7 message's
* list to see if the next one is there.
*/
pr_debug("- want %*phN\n",
x509->akid_skid->len, x509->akid_skid->data);
for (p = pkcs7->certs; p; p = p->next) {
if (!p->skid)
continue;
pr_debug("- cmp [%u] %*phN\n",
p->index, p->skid->len, p->skid->data);
if (asymmetric_key_id_same(p->skid, x509->akid_skid))
goto found_issuer;
}
/* We didn't find the root of this chain */
pr_debug("- top\n");
return 0;
found_issuer:
pr_debug("- subject %s\n", p->subject);
if (p->seen) {
pr_warn("Sig %u: X.509 chain contains loop\n",
sinfo->index);
return 0;
}
ret = x509_check_signature(p->pub, x509);
if (ret < 0)
return ret;
x509->signer = p;
if (x509 == p) {
pr_debug("- self-signed\n");
return 0;
}
x509 = p;
might_sleep();
}
maybe_missing_crypto_in_x509:
/* Just prune the certificate chain at this point if we lack some
* crypto module to go further. Note, however, we don't want to set
* sinfo->missing_crypto as the signed info block may still be
* validatable against an X.509 cert lower in the chain that we have a
* trusted copy of.
*/
if (ret == -ENOPKG)
return 0;
return ret;
}
/*
* Verify one signed information block from a PKCS#7 message.
*/
static int pkcs7_verify_one(struct pkcs7_message *pkcs7,
struct pkcs7_signed_info *sinfo)
{
int ret;
kenter(",%u", sinfo->index);
/* First of all, digest the data in the PKCS#7 message and the
* signed information block
*/
ret = pkcs7_digest(pkcs7, sinfo);
if (ret < 0)
return ret;
/* Find the key for the signature if there is one */
ret = pkcs7_find_key(pkcs7, sinfo);
if (ret < 0)
return ret;
if (!sinfo->signer)
return 0;
pr_devel("Using X.509[%u] for sig %u\n",
sinfo->signer->index, sinfo->index);
/* Verify the PKCS#7 binary against the key */
ret = public_key_verify_signature(sinfo->signer->pub, &sinfo->sig);
if (ret < 0)
return ret;
pr_devel("Verified signature %u\n", sinfo->index);
/* Verify the internal certificate chain */
return pkcs7_verify_sig_chain(pkcs7, sinfo);
}
/**
* pkcs7_verify - Verify a PKCS#7 message
* @pkcs7: The PKCS#7 message to be verified
*
* Verify a PKCS#7 message is internally consistent - that is, the data digest
* matches the digest in the AuthAttrs and any signature in the message or one
* of the X.509 certificates it carries that matches another X.509 cert in the
* message can be verified.
*
* This does not look to match the contents of the PKCS#7 message against any
* external public keys.
*
* Returns, in order of descending priority:
*
* (*) -EKEYREJECTED if a signature failed to match for which we found an
* appropriate X.509 certificate, or:
*
* (*) -EBADMSG if some part of the message was invalid, or:
*
* (*) -ENOPKG if none of the signature chains are verifiable because suitable
* crypto modules couldn't be found, or:
*
* (*) 0 if all the signature chains that don't incur -ENOPKG can be verified
* (note that a signature chain may be of zero length), or:
*/
int pkcs7_verify(struct pkcs7_message *pkcs7)
{
struct pkcs7_signed_info *sinfo;
struct x509_certificate *x509;
int enopkg = -ENOPKG;
int ret, n;
kenter("");
for (n = 0, x509 = pkcs7->certs; x509; x509 = x509->next, n++) {
ret = x509_get_sig_params(x509);
if (ret < 0)
return ret;
}
for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
ret = pkcs7_verify_one(pkcs7, sinfo);
if (ret < 0) {
if (ret == -ENOPKG) {
sinfo->unsupported_crypto = true;
continue;
}
kleave(" = %d", ret);
return ret;
}
enopkg = 0;
}
kleave(" = %d", enopkg);
return enopkg;
}
EXPORT_SYMBOL_GPL(pkcs7_verify);
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