// SPDX-License-Identifier: GPL-2.0-or-later
/* System hash blacklist.
 *
 * Copyright (C) 2016 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 */

#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/hex.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_obj(*restriction);
        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