security/integrity/digsig_asymmetric.c

/*
 * Copyright (C) 2013 Intel Corporation
 *
 * Author:
 * Dmitry Kasatkin <dmitry.kasatkin@intel.com>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, version 2 of the License.
 *
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/err.h>
#include <linux/ratelimit.h>
#include <linux/key-type.h>
#include <crypto/public_key.h>
#include <crypto/hash_info.h>
#include <keys/asymmetric-type.h>
#include <keys/system_keyring.h>

#include "integrity.h"

/*
 * Request an asymmetric key.
 */
static struct key *request_asymmetric_key(struct key *keyring, uint32_t keyid)
{
	struct key *key;
	char name[12];

	sprintf(name, "id:%08x", keyid);

	pr_debug("key search: \"%s\"\n", name);

	key = get_ima_blacklist_keyring();
	if (key) {
		key_ref_t kref;

		kref = keyring_search(make_key_ref(key, 1),
				     &key_type_asymmetric, name);
		if (!IS_ERR(kref)) {
			pr_err("Key '%s' is in ima_blacklist_keyring\n", name);
			return ERR_PTR(-EKEYREJECTED);
		}
	}

	if (keyring) {
		/* search in specific keyring */
		key_ref_t kref;

		kref = keyring_search(make_key_ref(keyring, 1),
				      &key_type_asymmetric, name);
		if (IS_ERR(kref))
			key = ERR_CAST(kref);
		else
			key = key_ref_to_ptr(kref);
	} else {
		key = request_key(&key_type_asymmetric, name, NULL);
	}

	if (IS_ERR(key)) {
		pr_err_ratelimited("Request for unknown key '%s' err %ld\n",
				   name, PTR_ERR(key));
		switch (PTR_ERR(key)) {
			/* Hide some search errors */
		case -EACCES:
		case -ENOTDIR:
		case -EAGAIN:
			return ERR_PTR(-ENOKEY);
		default:
			return key;
		}
	}

	pr_debug("%s() = 0 [%x]\n", __func__, key_serial(key));

	return key;
}

int asymmetric_verify(struct key *keyring, const char *sig,
		      int siglen, const char *data, int datalen)
{
	struct public_key_signature pks;
	struct signature_v2_hdr *hdr = (struct signature_v2_hdr *)sig;
	struct key *key;
	int ret = -ENOMEM;

	if (siglen <= sizeof(*hdr))
		return -EBADMSG;

	siglen -= sizeof(*hdr);

	if (siglen != be16_to_cpu(hdr->sig_size))
		return -EBADMSG;

	if (hdr->hash_algo >= HASH_ALGO__LAST)
		return -ENOPKG;

	key = request_asymmetric_key(keyring, be32_to_cpu(hdr->keyid));
	if (IS_ERR(key))
		return PTR_ERR(key);

	memset(&pks, 0, sizeof(pks));

	pks.pkey_algo = "rsa";
	pks.hash_algo = hash_algo_name[hdr->hash_algo];
	pks.encoding = "pkcs1";
	pks.digest = (u8 *)data;
	pks.digest_size = datalen;
	pks.s = hdr->sig;
	pks.s_size = siglen;
	ret = verify_signature(key, &pks);
	key_put(key);
	pr_debug("%s() = %d\n", __func__, ret);
	return ret;
}

/**
 * integrity_kernel_module_request - prevent crypto-pkcs1pad(rsa,*) requests
 * @kmod_name: kernel module name
 *
 * We have situation, when public_key_verify_signature() in case of RSA
 * algorithm use alg_name to store internal information in order to
 * construct an algorithm on the fly, but crypto_larval_lookup() will try
 * to use alg_name in order to load kernel module with same name.
 * Since we don't have any real "crypto-pkcs1pad(rsa,*)" kernel modules,
 * we are safe to fail such module request from crypto_larval_lookup().
 *
 * In this way we prevent modprobe execution during digsig verification
 * and avoid possible deadlock if modprobe and/or it's dependencies
 * also signed with digsig.
 */
int integrity_kernel_module_request(char *kmod_name)
{
	if (strncmp(kmod_name, "crypto-pkcs1pad(rsa,", 20) == 0)
		return -EINVAL;

	return 0;
}