2014-07-01 17:40:19 +02:00
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/* Verify the signature on a PKCS#7 message.
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*
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* Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
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* Written by David Howells (dhowells@redhat.com)
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public Licence
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* as published by the Free Software Foundation; either version
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* 2 of the Licence, or (at your option) any later version.
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*/
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#define pr_fmt(fmt) "PKCS7: "fmt
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#include <linux/kernel.h>
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#include <linux/export.h>
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#include <linux/slab.h>
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#include <linux/err.h>
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#include <linux/asn1.h>
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#include <crypto/hash.h>
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#include "public_key.h"
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#include "pkcs7_parser.h"
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/*
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* Digest the relevant parts of the PKCS#7 data
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*/
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static int pkcs7_digest(struct pkcs7_message *pkcs7,
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struct pkcs7_signed_info *sinfo)
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{
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struct crypto_shash *tfm;
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struct shash_desc *desc;
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size_t digest_size, desc_size;
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void *digest;
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int ret;
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kenter(",%u,%u", sinfo->index, sinfo->sig.pkey_hash_algo);
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if (sinfo->sig.pkey_hash_algo >= PKEY_HASH__LAST ||
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!hash_algo_name[sinfo->sig.pkey_hash_algo])
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return -ENOPKG;
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/* Allocate the hashing algorithm we're going to need and find out how
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* big the hash operational data will be.
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*/
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tfm = crypto_alloc_shash(hash_algo_name[sinfo->sig.pkey_hash_algo],
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0, 0);
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if (IS_ERR(tfm))
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return (PTR_ERR(tfm) == -ENOENT) ? -ENOPKG : PTR_ERR(tfm);
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desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
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sinfo->sig.digest_size = digest_size = crypto_shash_digestsize(tfm);
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ret = -ENOMEM;
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digest = kzalloc(digest_size + desc_size, GFP_KERNEL);
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if (!digest)
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goto error_no_desc;
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desc = digest + digest_size;
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desc->tfm = tfm;
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desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
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/* Digest the message [RFC2315 9.3] */
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ret = crypto_shash_init(desc);
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if (ret < 0)
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goto error;
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ret = crypto_shash_finup(desc, pkcs7->data, pkcs7->data_len, digest);
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if (ret < 0)
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goto error;
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pr_devel("MsgDigest = [%*ph]\n", 8, digest);
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/* However, if there are authenticated attributes, there must be a
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* message digest attribute amongst them which corresponds to the
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* digest we just calculated.
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*/
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if (sinfo->msgdigest) {
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u8 tag;
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if (sinfo->msgdigest_len != sinfo->sig.digest_size) {
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pr_debug("Sig %u: Invalid digest size (%u)\n",
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sinfo->index, sinfo->msgdigest_len);
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ret = -EBADMSG;
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goto error;
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}
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if (memcmp(digest, sinfo->msgdigest, sinfo->msgdigest_len) != 0) {
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pr_debug("Sig %u: Message digest doesn't match\n",
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sinfo->index);
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ret = -EKEYREJECTED;
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goto error;
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}
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/* We then calculate anew, using the authenticated attributes
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* as the contents of the digest instead. Note that we need to
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* convert the attributes from a CONT.0 into a SET before we
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* hash it.
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*/
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memset(digest, 0, sinfo->sig.digest_size);
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ret = crypto_shash_init(desc);
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if (ret < 0)
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goto error;
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tag = ASN1_CONS_BIT | ASN1_SET;
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ret = crypto_shash_update(desc, &tag, 1);
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if (ret < 0)
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goto error;
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ret = crypto_shash_finup(desc, sinfo->authattrs,
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sinfo->authattrs_len, digest);
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if (ret < 0)
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goto error;
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pr_devel("AADigest = [%*ph]\n", 8, digest);
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}
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sinfo->sig.digest = digest;
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digest = NULL;
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error:
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kfree(digest);
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error_no_desc:
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crypto_free_shash(tfm);
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kleave(" = %d", ret);
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return ret;
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}
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/*
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2014-07-01 17:40:19 +02:00
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* Find the key (X.509 certificate) to use to verify a PKCS#7 message. PKCS#7
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* uses the issuer's name and the issuing certificate serial number for
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* matching purposes. These must match the certificate issuer's name (not
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* subject's name) and the certificate serial number [RFC 2315 6.7].
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*/
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static int pkcs7_find_key(struct pkcs7_message *pkcs7,
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struct pkcs7_signed_info *sinfo)
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{
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struct x509_certificate *x509;
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unsigned certix = 1;
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kenter("%u,%u,%u",
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sinfo->index, sinfo->raw_serial_size, sinfo->raw_issuer_size);
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for (x509 = pkcs7->certs; x509; x509 = x509->next, certix++) {
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/* I'm _assuming_ that the generator of the PKCS#7 message will
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* encode the fields from the X.509 cert in the same way in the
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* PKCS#7 message - but I can't be 100% sure of that. It's
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* possible this will need element-by-element comparison.
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*/
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if (x509->raw_serial_size != sinfo->raw_serial_size ||
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memcmp(x509->raw_serial, sinfo->raw_serial,
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sinfo->raw_serial_size) != 0)
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continue;
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pr_devel("Sig %u: Found cert serial match X.509[%u]\n",
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sinfo->index, certix);
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if (x509->raw_issuer_size != sinfo->raw_issuer_size ||
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memcmp(x509->raw_issuer, sinfo->raw_issuer,
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sinfo->raw_issuer_size) != 0) {
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pr_warn("Sig %u: X.509 subject and PKCS#7 issuer don't match\n",
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sinfo->index);
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continue;
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}
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if (x509->pub->pkey_algo != sinfo->sig.pkey_algo) {
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pr_warn("Sig %u: X.509 algo and PKCS#7 sig algo don't match\n",
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sinfo->index);
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continue;
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}
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sinfo->signer = x509;
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return 0;
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}
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pr_warn("Sig %u: Issuing X.509 cert not found (#%*ph)\n",
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sinfo->index, sinfo->raw_serial_size, sinfo->raw_serial);
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return -ENOKEY;
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}
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2014-07-01 17:40:19 +02:00
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/*
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* Verify the internal certificate chain as best we can.
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*/
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static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7,
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struct pkcs7_signed_info *sinfo)
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{
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struct x509_certificate *x509 = sinfo->signer, *p;
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int ret;
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kenter("");
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for (p = pkcs7->certs; p; p = p->next)
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p->seen = false;
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for (;;) {
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pr_debug("verify %s: %s\n", x509->subject, x509->fingerprint);
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x509->seen = true;
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ret = x509_get_sig_params(x509);
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if (ret < 0)
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return ret;
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2014-07-31 15:46:44 +02:00
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pr_debug("- issuer %s\n", x509->issuer);
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2014-07-01 17:40:19 +02:00
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if (x509->authority)
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pr_debug("- authkeyid %s\n", x509->authority);
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if (!x509->authority ||
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2014-07-31 15:46:44 +02:00
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strcmp(x509->subject, x509->issuer) == 0) {
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2014-07-01 17:40:19 +02:00
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/* If there's no authority certificate specified, then
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* the certificate must be self-signed and is the root
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* of the chain. Likewise if the cert is its own
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* authority.
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*/
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pr_debug("- no auth?\n");
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if (x509->raw_subject_size != x509->raw_issuer_size ||
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memcmp(x509->raw_subject, x509->raw_issuer,
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x509->raw_issuer_size) != 0)
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return 0;
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ret = x509_check_signature(x509->pub, x509);
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if (ret < 0)
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return ret;
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x509->signer = x509;
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pr_debug("- self-signed\n");
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return 0;
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}
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/* Look through the X.509 certificates in the PKCS#7 message's
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* list to see if the next one is there.
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*/
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pr_debug("- want %s\n", x509->authority);
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for (p = pkcs7->certs; p; p = p->next) {
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pr_debug("- cmp [%u] %s\n", p->index, p->fingerprint);
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if (p->raw_subject_size == x509->raw_issuer_size &&
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strcmp(p->fingerprint, x509->authority) == 0 &&
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memcmp(p->raw_subject, x509->raw_issuer,
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x509->raw_issuer_size) == 0)
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goto found_issuer;
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}
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/* We didn't find the root of this chain */
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pr_debug("- top\n");
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return 0;
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found_issuer:
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pr_debug("- issuer %s\n", p->subject);
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if (p->seen) {
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pr_warn("Sig %u: X.509 chain contains loop\n",
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sinfo->index);
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return 0;
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}
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ret = x509_check_signature(p->pub, x509);
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if (ret < 0)
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return ret;
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x509->signer = p;
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if (x509 == p) {
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pr_debug("- self-signed\n");
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return 0;
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}
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x509 = p;
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might_sleep();
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}
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}
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2014-07-01 17:40:19 +02:00
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/*
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* Verify one signed information block from a PKCS#7 message.
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*/
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static int pkcs7_verify_one(struct pkcs7_message *pkcs7,
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struct pkcs7_signed_info *sinfo)
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{
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int ret;
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kenter(",%u", sinfo->index);
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/* First of all, digest the data in the PKCS#7 message and the
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* signed information block
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*/
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ret = pkcs7_digest(pkcs7, sinfo);
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if (ret < 0)
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return ret;
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2014-07-01 17:40:19 +02:00
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/* Find the key for the signature */
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ret = pkcs7_find_key(pkcs7, sinfo);
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if (ret < 0)
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return ret;
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pr_devel("Using X.509[%u] for sig %u\n",
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sinfo->signer->index, sinfo->index);
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/* Verify the PKCS#7 binary against the key */
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ret = public_key_verify_signature(sinfo->signer->pub, &sinfo->sig);
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if (ret < 0)
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return ret;
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pr_devel("Verified signature %u\n", sinfo->index);
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2014-07-01 17:40:19 +02:00
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/* Verify the internal certificate chain */
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return pkcs7_verify_sig_chain(pkcs7, sinfo);
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2014-07-01 17:40:19 +02:00
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}
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/**
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* pkcs7_verify - Verify a PKCS#7 message
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* @pkcs7: The PKCS#7 message to be verified
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*/
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int pkcs7_verify(struct pkcs7_message *pkcs7)
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{
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struct pkcs7_signed_info *sinfo;
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struct x509_certificate *x509;
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int ret, n;
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kenter("");
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for (n = 0, x509 = pkcs7->certs; x509; x509 = x509->next, n++) {
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ret = x509_get_sig_params(x509);
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if (ret < 0)
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return ret;
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pr_debug("X.509[%u] %s\n", n, x509->authority);
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}
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for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
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ret = pkcs7_verify_one(pkcs7, sinfo);
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if (ret < 0) {
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kleave(" = %d", ret);
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return ret;
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}
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}
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kleave(" = 0");
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return 0;
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}
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EXPORT_SYMBOL_GPL(pkcs7_verify);
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