blacklist.c 4.04 KB
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/* System hash blacklist.
 *
 * Copyright (C) 2016 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) "blacklist: "fmt
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/key.h>
#include <linux/key-type.h>
#include <linux/sched.h>
#include <linux/ctype.h>
#include <linux/err.h>
#include <linux/seq_file.h>
#include <keys/system_keyring.h>
#include "blacklist.h"

static struct key *blacklist_keyring;

/*
 * The description must be a type prefix, a colon and then an even number of
 * hex digits.  The hash is kept in the description.
 */
static int blacklist_vet_description(const char *desc)
{
	int n = 0;

	if (*desc == ':')
		return -EINVAL;
	for (; *desc; desc++)
		if (*desc == ':')
			goto found_colon;
	return -EINVAL;

found_colon:
	desc++;
	for (; *desc; desc++) {
		if (!isxdigit(*desc))
			return -EINVAL;
		n++;
	}

	if (n == 0 || n & 1)
		return -EINVAL;
	return 0;
}

/*
 * The hash to be blacklisted is expected to be in the description.  There will
 * be no payload.
 */
static int blacklist_preparse(struct key_preparsed_payload *prep)
{
	if (prep->datalen > 0)
		return -EINVAL;
	return 0;
}

static void blacklist_free_preparse(struct key_preparsed_payload *prep)
{
}

static void blacklist_describe(const struct key *key, struct seq_file *m)
{
	seq_puts(m, key->description);
}

static struct key_type key_type_blacklist = {
	.name			= "blacklist",
	.vet_description	= blacklist_vet_description,
	.preparse		= blacklist_preparse,
	.free_preparse		= blacklist_free_preparse,
	.instantiate		= generic_key_instantiate,
	.describe		= blacklist_describe,
};

/**
 * mark_hash_blacklisted - Add a hash to the system blacklist
 * @hash - The hash as a hex string with a type prefix (eg. "tbs:23aa429783")
 */
int mark_hash_blacklisted(const char *hash)
{
	key_ref_t key;

	key = key_create_or_update(make_key_ref(blacklist_keyring, true),
				   "blacklist",
				   hash,
				   NULL,
				   0,
				   ((KEY_POS_ALL & ~KEY_POS_SETATTR) |
				    KEY_USR_VIEW),
				   KEY_ALLOC_NOT_IN_QUOTA |
				   KEY_ALLOC_BUILT_IN);
	if (IS_ERR(key)) {
		pr_err("Problem blacklisting hash (%ld)\n", PTR_ERR(key));
		return PTR_ERR(key);
	}
	return 0;
}

/**
 * is_hash_blacklisted - Determine if a hash is blacklisted
 * @hash: The hash to be checked as a binary blob
 * @hash_len: The length of the binary hash
 * @type: Type of hash
 */
int is_hash_blacklisted(const u8 *hash, size_t hash_len, const char *type)
{
	key_ref_t kref;
	size_t type_len = strlen(type);
	char *buffer, *p;
	int ret = 0;

	buffer = kmalloc(type_len + 1 + hash_len * 2 + 1, GFP_KERNEL);
	if (!buffer)
		return -ENOMEM;
	p = memcpy(buffer, type, type_len);
	p += type_len;
	*p++ = ':';
	bin2hex(p, hash, hash_len);
	p += hash_len * 2;
	*p = 0;

	kref = keyring_search(make_key_ref(blacklist_keyring, true),
			      &key_type_blacklist, buffer);
	if (!IS_ERR(kref)) {
		key_ref_put(kref);
		ret = -EKEYREJECTED;
	}

	kfree(buffer);
	return ret;
}
EXPORT_SYMBOL_GPL(is_hash_blacklisted);

/*
143
 * Initialise the blacklist
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
 */
static int __init blacklist_init(void)
{
	const char *const *bl;

	if (register_key_type(&key_type_blacklist) < 0)
		panic("Can't allocate system blacklist key type\n");

	blacklist_keyring =
		keyring_alloc(".blacklist",
			      KUIDT_INIT(0), KGIDT_INIT(0),
			      current_cred(),
			      (KEY_POS_ALL & ~KEY_POS_SETATTR) |
			      KEY_USR_VIEW | KEY_USR_READ |
			      KEY_USR_SEARCH,
			      KEY_ALLOC_NOT_IN_QUOTA |
			      KEY_FLAG_KEEP,
			      NULL, NULL);
	if (IS_ERR(blacklist_keyring))
		panic("Can't allocate system blacklist keyring\n");

	for (bl = blacklist_hashes; *bl; bl++)
		if (mark_hash_blacklisted(*bl) < 0)
			pr_err("- blacklisting failed\n");
	return 0;
}

/*
 * Must be initialised before we try and load the keys into the keyring.
 */
device_initcall(blacklist_init);