// SPDX-License-Identifier: GPL-2.0-or-later
/* System hash blacklist.
*
* Copyright (C) 2016 Red Hat, Inc. All Rights Reserved.
* Written by David Howells ([email protected])
*/
#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 <linux/uidgid.h>
#include <keys/asymmetric-type.h>
#include <keys/system_keyring.h>
#include "blacklist.h"
/*
* According to crypto/asymmetric_keys/x509_cert_parser.c:x509_note_pkey_algo(),
* the size of the currently longest supported hash algorithm is 512 bits,
* which translates into 128 hex characters.
*/
#define MAX_HASH_LEN 128
#define BLACKLIST_KEY_PERM (KEY_POS_SEARCH | KEY_POS_VIEW | \
KEY_USR_SEARCH | KEY_USR_VIEW)
static const char tbs_prefix[] = "tbs";
static const char bin_prefix[] = "bin";
static struct key *blacklist_keyring;
#ifdef CONFIG_SYSTEM_REVOCATION_LIST
extern __initconst const u8 revocation_certificate_list[];
extern __initconst const unsigned long revocation_certificate_list_size;
#endif
/*
* 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 i, prefix_len, tbs_step = 0, bin_step = 0;
/* The following algorithm only works if prefix lengths match. */
BUILD_BUG_ON(sizeof(tbs_prefix) != sizeof(bin_prefix));
prefix_len = sizeof(tbs_prefix) - 1;
for (i = 0; *desc; desc++, i++) {
if (*desc == ':') {
if (tbs_step == prefix_len)
goto found_colon;
if (bin_step == prefix_len)
goto found_colon;
return -EINVAL;
}
if (i >= prefix_len)
return -EINVAL;
if (*desc == tbs_prefix[i])
tbs_step++;
if (*desc == bin_prefix[i])
bin_step++;
}
return -EINVAL;
found_colon:
desc++;
for (i = 0; *desc && i < MAX_HASH_LEN; desc++, i++) {
if (!isxdigit(*desc) || isupper(*desc))
return -EINVAL;
}
if (*desc)
/* The hash is greater than MAX_HASH_LEN. */
return -ENOPKG;
/* Checks for an even number of hexadecimal characters. */
if (i == 0 || i & 1)
return -EINVAL;
return 0;
}
static int blacklist_key_instantiate(struct key *key,
struct key_preparsed_payload *prep)
{
#ifdef CONFIG_SYSTEM_BLACKLIST_AUTH_UPDATE
int err;
#endif
/* Sets safe default permissions for keys loaded by user space. */
key->perm = BLACKLIST_KEY_PERM;
/*
* Skips the authentication step for builtin hashes, they are not
* signed but still trusted.
*/
if (key->flags & (1 << KEY_FLAG_BUILTIN))
goto out;
#ifdef CONFIG_SYSTEM_BLACKLIST_AUTH_UPDATE
/*
* Verifies the description's PKCS#7 signature against the builtin
* trusted keyring.
*/
err = verify_pkcs7_signature(key->description,
strlen(key->description), prep->data, prep->datalen,
NULL, VERIFYING_UNSPECIFIED_SIGNATURE, NULL, NULL);
if (err)
return err;
#else
/*
* It should not be possible to come here because the keyring doesn't
* have KEY_USR_WRITE and the only other way to call this function is
* for builtin hashes.
*/
WARN_ON_ONCE(1);
return -EPERM;
#endif
out:
return generic_key_instantiate(key, prep);
}
static int blacklist_key_update(struct key *key,
struct key_preparsed_payload *prep)
{
return -EPERM;
}
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,
.instantiate = blacklist_key_instantiate,
.update = blacklist_key_update,
.describe = blacklist_describe,
};
static char *get_raw_hash(const u8 *hash, size_t hash_len,
enum blacklist_hash_type hash_type)
{
size_t type_len;
const char *type_prefix;
char *buffer, *p;
switch (hash_type) {
case BLACKLIST_HASH_X509_TBS:
type_len = sizeof(tbs_prefix) - 1;
type_prefix = tbs_prefix;
break;
case BLACKLIST_HASH_BINARY:
type_len = sizeof(bin_prefix) - 1;
type_prefix = bin_prefix;
break;
default:
WARN_ON_ONCE(1);
return ERR_PTR(-EINVAL);
}
buffer = kmalloc(type_len + 1 + hash_len * 2 + 1, GFP_KERNEL);
if (!buffer)
return ERR_PTR(-ENOMEM);
p = memcpy(buffer, type_prefix, type_len);
p += type_len;
*p++ = ':';
bin2hex(p, hash, hash_len);
p += hash_len * 2;
*p = '\0';
return buffer;
}
/**
* mark_raw_hash_blacklisted - Add a hash to the system blacklist
* @hash: The hash as a hex string with a type prefix (eg. "tbs:23aa429783")
*/
static int mark_raw_hash_blacklisted(const char *hash)
{
key_ref_t key;
key = key_create(make_key_ref(blacklist_keyring, true),
"blacklist",
hash,
NULL,
0,
BLACKLIST_KEY_PERM,
KEY_ALLOC_NOT_IN_QUOTA |
KEY_ALLOC_BUILT_IN);
if (IS_ERR(key)) {
if (PTR_ERR(key) == -EEXIST)
pr_warn("Duplicate blacklisted hash %s\n", hash);
else
pr_err("Problem blacklisting hash %s: %pe\n", hash, key);
return PTR_ERR(key);
}
return 0;
}
int mark_hash_blacklisted(const u8 *hash, size_t hash_len,
enum blacklist_hash_type hash_type)
{
const char *buffer;
int err;
buffer = get_raw_hash(hash, hash_len, hash_type);
if (IS_ERR(buffer))
return PTR_ERR(buffer);
err = mark_raw_hash_blacklisted(buffer);
kfree(buffer);
return err;
}
/**
* 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
* @hash_type: Type of hash
*/
int is_hash_blacklisted(const u8 *hash, size_t hash_len,
enum blacklist_hash_type hash_type)
{
key_ref_t kref;
const char *buffer;
int ret = 0;
buffer = get_raw_hash(hash, hash_len, hash_type);
if (IS_ERR(buffer))
return PTR_ERR(buffer);
kref = keyring_search(make_key_ref(blacklist_keyring, true),
&key_type_blacklist, buffer, false);
if (!IS_ERR(kref)) {
key_ref_put(kref);
ret = -EKEYREJECTED;
}
kfree(buffer);
return ret;
}
EXPORT_SYMBOL_GPL(is_hash_blacklisted);
int is_binary_blacklisted(const u8 *hash, size_t hash_len)
{
if (is_hash_blacklisted(hash, hash_len, BLACKLIST_HASH_BINARY) ==
-EKEYREJECTED)
return -EPERM;
return 0;
}
EXPORT_SYMBOL_GPL(is_binary_blacklisted);
#ifdef CONFIG_SYSTEM_REVOCATION_LIST
/**
* add_key_to_revocation_list - Add a revocation certificate to the blacklist
* @data: The data blob containing the certificate
* @size: The size of data blob
*/
int add_key_to_revocation_list(const char *data, size_t size)
{
key_ref_t key;
key = key_create_or_update(make_key_ref(blacklist_keyring, true),
"asymmetric",
NULL,
data,
size,
KEY_POS_VIEW | KEY_POS_READ | KEY_POS_SEARCH
| KEY_USR_VIEW,
KEY_ALLOC_NOT_IN_QUOTA | KEY_ALLOC_BUILT_IN
| KEY_ALLOC_BYPASS_RESTRICTION);
if (IS_ERR(key)) {
pr_err("Problem with revocation key (%ld)\n", PTR_ERR(key));
return PTR_ERR(key);
}
return 0;
}
/**
* is_key_on_revocation_list - Determine if the key for a PKCS#7 message is revoked
* @pkcs7: The PKCS#7 message to check
*/
int is_key_on_revocation_list(struct pkcs7_message *pkcs7)
{
int ret;
ret = pkcs7_validate_trust(pkcs7, blacklist_keyring);
if (ret == 0)
return -EKEYREJECTED;
return -ENOKEY;
}
#endif
static int restrict_link_for_blacklist(struct key *dest_keyring,
const struct key_type *type, const union key_payload *payload,
struct key *restrict_key)
{
if (type == &key_type_blacklist)
return 0;
return -EOPNOTSUPP;
}
/*
* Initialise the blacklist
*
* The blacklist_init() function is registered as an initcall via
* device_initcall(). As a result if the blacklist_init() function fails for
* any reason the kernel continues to execute. While cleanly returning -ENODEV
* could be acceptable for some non-critical kernel parts, if the blacklist
* keyring fails to load it defeats the certificate/key based deny list for
* signed modules. If a critical piece of security functionality that users
* expect to be present fails to initialize, panic()ing is likely the right
* thing to do.
*/
static int __init blacklist_init(void)
{
const char *const *bl;
struct key_restriction *restriction;
if (register_key_type(&key_type_blacklist) < 0)
panic("Can't allocate system blacklist key type\n");
restriction = kzalloc(sizeof(*restriction), GFP_KERNEL);
if (!restriction)
panic("Can't allocate blacklist keyring restriction\n");
restriction->check = restrict_link_for_blacklist;
blacklist_keyring =
keyring_alloc(".blacklist",
GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, current_cred(),
KEY_POS_VIEW | KEY_POS_READ | KEY_POS_SEARCH |
KEY_POS_WRITE |
KEY_USR_VIEW | KEY_USR_READ | KEY_USR_SEARCH
#ifdef CONFIG_SYSTEM_BLACKLIST_AUTH_UPDATE
| KEY_USR_WRITE
#endif
, KEY_ALLOC_NOT_IN_QUOTA |
KEY_ALLOC_SET_KEEP,
restriction, NULL);
if (IS_ERR(blacklist_keyring))
panic("Can't allocate system blacklist keyring\n");
for (bl = blacklist_hashes; *bl; bl++)
if (mark_raw_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);
#ifdef CONFIG_SYSTEM_REVOCATION_LIST
/*
* Load the compiled-in list of revocation X.509 certificates.
*/
static __init int load_revocation_certificate_list(void)
{
if (revocation_certificate_list_size)
pr_notice("Loading compiled-in revocation X.509 certificates\n");
return x509_load_certificate_list(revocation_certificate_list,
revocation_certificate_list_size,
blacklist_keyring);
}
late_initcall(load_revocation_certificate_list);
#endif
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