// SPDX-License-Identifier: GPL-2.0-or-later
/* Verify the signature on a PKCS#7 message.
*
* Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
* Written by David Howells ([email protected])
*/
#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 <crypto/hash_info.h>
#include <crypto/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 public_key_signature *sig = sinfo->sig;
struct crypto_shash *tfm;
struct shash_desc *desc;
size_t desc_size;
int ret;
kenter(",%u,%s", sinfo->index, sinfo->sig->hash_algo);
/* The digest was calculated already. */
if (sig->digest)
return 0;
if (!sinfo->sig->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(sinfo->sig->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);
sig->digest_size = crypto_shash_digestsize(tfm);
ret = -ENOMEM;
sig->digest = kmalloc(sig->digest_size, GFP_KERNEL);
if (!sig->digest)
goto error_no_desc;
desc = kzalloc(desc_size, GFP_KERNEL);
if (!desc)
goto error_no_desc;
desc->tfm = tfm;
/* Digest the message [RFC2315 9.3] */
ret = crypto_shash_digest(desc, pkcs7->data, pkcs7->data_len,
sig->digest);
if (ret < 0)
goto error;
pr_devel("MsgDigest = [%*ph]\n", 8, sig->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->authattrs) {
u8 tag;
if (!sinfo->msgdigest) {
pr_warn("Sig %u: No messageDigest\n", sinfo->index);
ret = -EKEYREJECTED;
goto error;
}
if (sinfo->msgdigest_len != sig->digest_size) {
pr_warn("Sig %u: Invalid digest size (%u)\n",
sinfo->index, sinfo->msgdigest_len);
ret = -EBADMSG;
goto error;
}
if (memcmp(sig->digest, sinfo->msgdigest,
sinfo->msgdigest_len) != 0) {
pr_warn("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(sig->digest, 0, 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, sig->digest);
if (ret < 0)
goto error;
pr_devel("AADigest = [%*ph]\n", 8, sig->digest);
}
error:
kfree(desc);
error_no_desc:
crypto_free_shash(tfm);
kleave(" = %d", ret);
return ret;
}
int pkcs7_get_digest(struct pkcs7_message *pkcs7, const u8 **buf, u32 *len,
enum hash_algo *hash_algo)
{
struct pkcs7_signed_info *sinfo = pkcs7->signed_infos;
int i, ret;
/*
* This function doesn't support messages with more than one signature.
*/
if (sinfo == NULL || sinfo->next != NULL)
return -EBADMSG;
ret = pkcs7_digest(pkcs7, sinfo);
if (ret)
return ret;
*buf = sinfo->sig->digest;
*len = sinfo->sig->digest_size;
i = match_string(hash_algo_name, HASH_ALGO__LAST,
sinfo->sig->hash_algo);
if (i >= 0)
*hash_algo = i;
return 0;
}
/*
* 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->sig->auth_ids[0]))
continue;
pr_devel("Sig %u: Found cert serial match X.509[%u]\n",
sinfo->index, certix);
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->sig->auth_ids[0]->len, sinfo->sig->auth_ids[0]->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 public_key_signature *sig;
struct x509_certificate *x509 = sinfo->signer, *p;
struct asymmetric_key_id *auth;
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;
if (x509->blacklisted) {
/* If this cert is blacklisted, then mark everything
* that depends on this as blacklisted too.
*/
sinfo->blacklisted = true;
for (p = sinfo->signer; p != x509; p = p->signer)
p->blacklisted = true;
pr_debug("- blacklisted\n");
return 0;
}
pr_debug("- issuer %s\n", x509->issuer);
sig = x509->sig;
if (sig->auth_ids[0])
pr_debug("- authkeyid.id %*phN\n",
sig->auth_ids[0]->len, sig->auth_ids[0]->data);
if (sig->auth_ids[1])
pr_debug("- authkeyid.skid %*phN\n",
sig->auth_ids[1]->len, sig->auth_ids[1]->data);
if (x509->self_signed) {
/* 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.
*/
if (x509->unsupported_sig)
goto unsupported_sig_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.
*/
auth = sig->auth_ids[0];
if (auth) {
pr_debug("- want %*phN\n", auth->len, auth->data);
for (p = pkcs7->certs; p; p = p->next) {
pr_debug("- cmp [%u] %*phN\n",
p->index, p->id->len, p->id->data);
if (asymmetric_key_id_same(p->id, auth))
goto found_issuer_check_skid;
}
} else if (sig->auth_ids[1]) {
auth = sig->auth_ids[1];
pr_debug("- want %*phN\n", auth->len, auth->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, auth))
goto found_issuer;
}
}
/* We didn't find the root of this chain */
pr_debug("- top\n");
return 0;
found_issuer_check_skid:
/* We matched issuer + serialNumber, but if there's an
* authKeyId.keyId, that must match the CA subjKeyId also.
*/
if (sig->auth_ids[1] &&
!asymmetric_key_id_same(p->skid, sig->auth_ids[1])) {
pr_warn("Sig %u: X.509 chain contains auth-skid nonmatch (%u->%u)\n",
sinfo->index, x509->index, p->index);
return -EKEYREJECTED;
}
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 = public_key_verify_signature(p->pub, x509->sig);
if (ret < 0)
return ret;
x509->signer = p;
if (x509 == p) {
pr_debug("- self-signed\n");
return 0;
}
x509 = p;
might_sleep();
}
unsupported_sig_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->unsupported_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.
*/
return 0;
}
/*
* 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);
/* Check that the PKCS#7 signing time is valid according to the X.509
* certificate. We can't, however, check against the system clock
* since that may not have been set yet and may be wrong.
*/
if (test_bit(sinfo_has_signing_time, &sinfo->aa_set)) {
if (sinfo->signing_time < sinfo->signer->valid_from ||
sinfo->signing_time > sinfo->signer->valid_to) {
pr_warn("Message signed outside of X.509 validity window\n");
return -EKEYREJECTED;
}
}
/* 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
* @usage: The use to which the key is being put
*
* 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 key was selected that had a usage restriction at
* odds with the specified usage, or:
*
* (*) -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:
*
* (*) 0 if a signature chain passed verification, or:
*
* (*) -EKEYREJECTED if a blacklisted key was encountered, or:
*
* (*) -ENOPKG if none of the signature chains are verifiable because suitable
* crypto modules couldn't be found.
*/
int pkcs7_verify(struct pkcs7_message *pkcs7,
enum key_being_used_for usage)
{
struct pkcs7_signed_info *sinfo;
int actual_ret = -ENOPKG;
int ret;
kenter("");
switch (usage) {
case VERIFYING_MODULE_SIGNATURE:
if (pkcs7->data_type != OID_data) {
pr_warn("Invalid module sig (not pkcs7-data)\n");
return -EKEYREJECTED;
}
if (pkcs7->have_authattrs) {
pr_warn("Invalid module sig (has authattrs)\n");
return -EKEYREJECTED;
}
break;
case VERIFYING_FIRMWARE_SIGNATURE:
if (pkcs7->data_type != OID_data) {
pr_warn("Invalid firmware sig (not pkcs7-data)\n");
return -EKEYREJECTED;
}
if (!pkcs7->have_authattrs) {
pr_warn("Invalid firmware sig (missing authattrs)\n");
return -EKEYREJECTED;
}
break;
case VERIFYING_KEXEC_PE_SIGNATURE:
if (pkcs7->data_type != OID_msIndirectData) {
pr_warn("Invalid kexec sig (not Authenticode)\n");
return -EKEYREJECTED;
}
/* Authattr presence checked in parser */
break;
case VERIFYING_UNSPECIFIED_SIGNATURE:
if (pkcs7->data_type != OID_data) {
pr_warn("Invalid unspecified sig (not pkcs7-data)\n");
return -EKEYREJECTED;
}
break;
default:
return -EINVAL;
}
for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
ret = pkcs7_verify_one(pkcs7, sinfo);
if (sinfo->blacklisted) {
if (actual_ret == -ENOPKG)
actual_ret = -EKEYREJECTED;
continue;
}
if (ret < 0) {
if (ret == -ENOPKG) {
sinfo->unsupported_crypto = true;
continue;
}
kleave(" = %d", ret);
return ret;
}
actual_ret = 0;
}
kleave(" = %d", actual_ret);
return actual_ret;
}
EXPORT_SYMBOL_GPL(pkcs7_verify);
/**
* pkcs7_supply_detached_data - Supply the data needed to verify a PKCS#7 message
* @pkcs7: The PKCS#7 message
* @data: The data to be verified
* @datalen: The amount of data
*
* Supply the detached data needed to verify a PKCS#7 message. Note that no
* attempt to retain/pin the data is made. That is left to the caller. The
* data will not be modified by pkcs7_verify() and will not be freed when the
* PKCS#7 message is freed.
*
* Returns -EINVAL if data is already supplied in the message, 0 otherwise.
*/
int pkcs7_supply_detached_data(struct pkcs7_message *pkcs7,
const void *data, size_t datalen)
{
if (pkcs7->data) {
pr_warn("Data already supplied\n");
return -EINVAL;
}
pkcs7->data = data;
pkcs7->data_len = datalen;
return 0;
}
EXPORT_SYMBOL_GPL(pkcs7_supply_detached_data);
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