// SPDX-License-Identifier: GPL-2.0
/*
 * This file is part of UBIFS.
 *
 * Copyright (C) 2018 Pengutronix, Sascha Hauer <s.hauer@pengutronix.de>
 */

/*
 * This file implements various helper functions for UBIFS authentication support
 */

#include <linux/crypto.h>
#include <linux/verification.h>
#include <crypto/hash.h>
#include <crypto/sha.h>
#include <crypto/algapi.h>
#include <keys/user-type.h>
#include <keys/asymmetric-type.h>

#include "ubifs.h"

/**
 * ubifs_node_calc_hash - calculate the hash of a UBIFS node
 * @c: UBIFS file-system description object
 * @node: the node to calculate a hash for
 * @hash: the returned hash
 *
 * Returns 0 for success or a negative error code otherwise.
 */
int __ubifs_node_calc_hash(const struct ubifs_info *c, const void *node,
                            u8 *hash)
{
        const struct ubifs_ch *ch = node;

        return crypto_shash_tfm_digest(c->hash_tfm, node, le32_to_cpu(ch->len),
                                       hash);
}

/**
 * ubifs_hash_calc_hmac - calculate a HMAC from a hash
 * @c: UBIFS file-system description object
 * @hash: the node to calculate a HMAC for
 * @hmac: the returned HMAC
 *
 * Returns 0 for success or a negative error code otherwise.
 */
static int ubifs_hash_calc_hmac(const struct ubifs_info *c, const u8 *hash,
                                 u8 *hmac)
{
        return crypto_shash_tfm_digest(c->hmac_tfm, hash, c->hash_len, hmac);
}

/**
 * ubifs_prepare_auth_node - Prepare an authentication node
 * @c: UBIFS file-system description object
 * @node: the node to calculate a hash for
 * @hash: input hash of previous nodes
 *
 * This function prepares an authentication node for writing onto flash.
 * It creates a HMAC from the given input hash and writes it to the node.
 *
 * Returns 0 for success or a negative error code otherwise.
 */
int ubifs_prepare_auth_node(struct ubifs_info *c, void *node,
                             struct shash_desc *inhash)
{
        struct ubifs_auth_node *auth = node;
        u8 hash[UBIFS_HASH_ARR_SZ];
        int err;

        {
                SHASH_DESC_ON_STACK(hash_desc, c->hash_tfm);

                hash_desc->tfm = c->hash_tfm;
                ubifs_shash_copy_state(c, inhash, hash_desc);

                err = crypto_shash_final(hash_desc, hash);
                if (err)
                        return err;
        }

        err = ubifs_hash_calc_hmac(c, hash, auth->hmac);
        if (err)
                return err;

        auth->ch.node_type = UBIFS_AUTH_NODE;
        ubifs_prepare_node(c, auth, ubifs_auth_node_sz(c), 0);
        return 0;
}

static struct shash_desc *ubifs_get_desc(const struct ubifs_info *c,
                                         struct crypto_shash *tfm)
{
        struct shash_desc *desc;
        int err;

        if (!ubifs_authenticated(c))
                return NULL;

        desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(tfm), GFP_KERNEL);
        if (!desc)
                return ERR_PTR(-ENOMEM);

        desc->tfm = tfm;

        err = crypto_shash_init(desc);
        if (err) {
                kfree(desc);
                return ERR_PTR(err);
        }

        return desc;
}

/**
 * __ubifs_hash_get_desc - get a descriptor suitable for hashing a node
 * @c: UBIFS file-system description object
 *
 * This function returns a descriptor suitable for hashing a node. Free after use
 * with kfree.
 */
struct shash_desc *__ubifs_hash_get_desc(const struct ubifs_info *c)
{
        return ubifs_get_desc(c, c->hash_tfm);
}

/**
 * ubifs_bad_hash - Report hash mismatches
 * @c: UBIFS file-system description object
 * @node: the node
 * @hash: the expected hash
 * @lnum: the LEB @node was read from
 * @offs: offset in LEB @node was read from
 *
 * This function reports a hash mismatch when a node has a different hash than
 * expected.
 */
void ubifs_bad_hash(const struct ubifs_info *c, const void *node, const u8 *hash,
                    int lnum, int offs)
{
        int len = min(c->hash_len, 20);
        int cropped = len != c->hash_len;
        const char *cont = cropped ? "..." : "";

        u8 calc[UBIFS_HASH_ARR_SZ];

        __ubifs_node_calc_hash(c, node, calc);

        ubifs_err(c, "hash mismatch on node at LEB %d:%d", lnum, offs);
        ubifs_err(c, "hash expected:   %*ph%s", len, hash, cont);
        ubifs_err(c, "hash calculated: %*ph%s", len, calc, cont);
}

/**
 * __ubifs_node_check_hash - check the hash of a node against given hash
 * @c: UBIFS file-system description object
 * @node: the node
 * @expected: the expected hash
 *
 * This function calculates a hash over a node and compares it to the given hash.
 * Returns 0 if both hashes are equal or authentication is disabled, otherwise a
 * negative error code is returned.
 */
int __ubifs_node_check_hash(const struct ubifs_info *c, const void *node,
                            const u8 *expected)
{
        u8 calc[UBIFS_HASH_ARR_SZ];
        int err;

        err = __ubifs_node_calc_hash(c, node, calc);
        if (err)
                return err;

        if (ubifs_check_hash(c, expected, calc))
                return -EPERM;

        return 0;
}

/**
 * ubifs_sb_verify_signature - verify the signature of a superblock
 * @c: UBIFS file-system description object
 * @sup: The superblock node
 *
 * To support offline signed images the superblock can be signed with a
 * PKCS#7 signature. The signature is placed directly behind the superblock
 * node in an ubifs_sig_node.
 *
 * Returns 0 when the signature can be successfully verified or a negative
 * error code if not.
 */
int ubifs_sb_verify_signature(struct ubifs_info *c,
                              const struct ubifs_sb_node *sup)
{
        int err;
        struct ubifs_scan_leb *sleb;
        struct ubifs_scan_node *snod;
        const struct ubifs_sig_node *signode;

        sleb = ubifs_scan(c, UBIFS_SB_LNUM, UBIFS_SB_NODE_SZ, c->sbuf, 0);
        if (IS_ERR(sleb)) {
                err = PTR_ERR(sleb);
                return err;
        }

        if (sleb->nodes_cnt == 0) {
                ubifs_err(c, "Unable to find signature node");
                err = -EINVAL;
                goto out_destroy;
        }

        snod = list_first_entry(&sleb->nodes, struct ubifs_scan_node, list);

        if (snod->type != UBIFS_SIG_NODE) {
                ubifs_err(c, "Signature node is of wrong type");
                err = -EINVAL;
                goto out_destroy;
        }

        signode = snod->node;

        if (le32_to_cpu(signode->len) > snod->len + sizeof(struct ubifs_sig_node)) {
                ubifs_err(c, "invalid signature len %d", le32_to_cpu(signode->len));
                err = -EINVAL;
                goto out_destroy;
        }

        if (le32_to_cpu(signode->type) != UBIFS_SIGNATURE_TYPE_PKCS7) {
                ubifs_err(c, "Signature type %d is not supported\n",
                          le32_to_cpu(signode->type));
                err = -EINVAL;
                goto out_destroy;
        }

        err = verify_pkcs7_signature(sup, sizeof(struct ubifs_sb_node),
                                     signode->sig, le32_to_cpu(signode->len),
                                     NULL, VERIFYING_UNSPECIFIED_SIGNATURE,
                                     NULL, NULL);

        if (err)
                ubifs_err(c, "Failed to verify signature");
        else
                ubifs_msg(c, "Successfully verified super block signature");

out_destroy:
        ubifs_scan_destroy(sleb);

        return err;
}

/**
 * ubifs_init_authentication - initialize UBIFS authentication support
 * @c: UBIFS file-system description object
 *
 * This function returns 0 for success or a negative error code otherwise.
 */
int ubifs_init_authentication(struct ubifs_info *c)
{
        struct key *keyring_key;
        const struct user_key_payload *ukp;
        int err;
        char hmac_name[CRYPTO_MAX_ALG_NAME];

        if (!c->auth_hash_name) {
                ubifs_err(c, "authentication hash name needed with authentication");
                return -EINVAL;
        }

        c->auth_hash_algo = match_string(hash_algo_name, HASH_ALGO__LAST,
                                         c->auth_hash_name);
        if ((int)c->auth_hash_algo < 0) {
                ubifs_err(c, "Unknown hash algo %s specified",
                          c->auth_hash_name);
                return -EINVAL;
        }

        snprintf(hmac_name, CRYPTO_MAX_ALG_NAME, "hmac(%s)",
                 c->auth_hash_name);

        keyring_key = request_key(&key_type_logon, c->auth_key_name, NULL);

        if (IS_ERR(keyring_key)) {
                ubifs_err(c, "Failed to request key: %ld",
                          PTR_ERR(keyring_key));
                return PTR_ERR(keyring_key);
        }

        down_read(&keyring_key->sem);

        if (keyring_key->type != &key_type_logon) {
                ubifs_err(c, "key type must be logon");
                err = -ENOKEY;
                goto out;
        }

        ukp = user_key_payload_locked(keyring_key);
        if (!ukp) {
                /* key was revoked before we acquired its semaphore */
                err = -EKEYREVOKED;
                goto out;
        }

        c->hash_tfm = crypto_alloc_shash(c->auth_hash_name, 0, 0);
        if (IS_ERR(c->hash_tfm)) {
                err = PTR_ERR(c->hash_tfm);
                ubifs_err(c, "Can not allocate %s: %d",
                          c->auth_hash_name, err);
                goto out;
        }

        c->hash_len = crypto_shash_digestsize(c->hash_tfm);
        if (c->hash_len > UBIFS_HASH_ARR_SZ) {
                ubifs_err(c, "hash %s is bigger than maximum allowed hash size (%d > %d)",
                          c->auth_hash_name, c->hash_len, UBIFS_HASH_ARR_SZ);
                err = -EINVAL;
                goto out_free_hash;
        }

        c->hmac_tfm = crypto_alloc_shash(hmac_name, 0, 0);
        if (IS_ERR(c->hmac_tfm)) {
                err = PTR_ERR(c->hmac_tfm);
                ubifs_err(c, "Can not allocate %s: %d", hmac_name, err);
                goto out_free_hash;
        }

        c->hmac_desc_len = crypto_shash_digestsize(c->hmac_tfm);
        if (c->hmac_desc_len > UBIFS_HMAC_ARR_SZ) {
                ubifs_err(c, "hmac %s is bigger than maximum allowed hmac size (%d > %d)",
                          hmac_name, c->hmac_desc_len, UBIFS_HMAC_ARR_SZ);
                err = -EINVAL;
                goto out_free_hash;
        }

        err = crypto_shash_setkey(c->hmac_tfm, ukp->data, ukp->datalen);
        if (err)
                goto out_free_hmac;

        c->authenticated = true;

        c->log_hash = ubifs_hash_get_desc(c);
        if (IS_ERR(c->log_hash))
                goto out_free_hmac;

        err = 0;

out_free_hmac:
        if (err)
                crypto_free_shash(c->hmac_tfm);
out_free_hash:
        if (err)
                crypto_free_shash(c->hash_tfm);
out:
        up_read(&keyring_key->sem);
        key_put(keyring_key);

        return err;
}

/**
 * __ubifs_exit_authentication - release resource
 * @c: UBIFS file-system description object
 *
 * This function releases the authentication related resources.
 */
void __ubifs_exit_authentication(struct ubifs_info *c)
{
        if (!ubifs_authenticated(c))
                return;

        crypto_free_shash(c->hmac_tfm);
        crypto_free_shash(c->hash_tfm);
        kfree(c->log_hash);
}

/**
 * ubifs_node_calc_hmac - calculate the HMAC of a UBIFS node
 * @c: UBIFS file-system description object
 * @node: the node to insert a HMAC into.
 * @len: the length of the node
 * @ofs_hmac: the offset in the node where the HMAC is inserted
 * @hmac: returned HMAC
 *
 * This function calculates a HMAC of a UBIFS node. The HMAC is expected to be
 * embedded into the node, so this area is not covered by the HMAC. Also not
 * covered is the UBIFS_NODE_MAGIC and the CRC of the node.
 */
static int ubifs_node_calc_hmac(const struct ubifs_info *c, const void *node,
                                int len, int ofs_hmac, void *hmac)
{
        SHASH_DESC_ON_STACK(shash, c->hmac_tfm);
        int hmac_len = c->hmac_desc_len;
        int err;

        ubifs_assert(c, ofs_hmac > 8);
        ubifs_assert(c, ofs_hmac + hmac_len < len);

        shash->tfm = c->hmac_tfm;

        err = crypto_shash_init(shash);
        if (err)
                return err;

        /* behind common node header CRC up to HMAC begin */
        err = crypto_shash_update(shash, node + 8, ofs_hmac - 8);
        if (err < 0)
                return err;

        /* behind HMAC, if any */
        if (len - ofs_hmac - hmac_len > 0) {
                err = crypto_shash_update(shash, node + ofs_hmac + hmac_len,
                            len - ofs_hmac - hmac_len);
                if (err < 0)
                        return err;
        }

        return crypto_shash_final(shash, hmac);
}

/**
 * __ubifs_node_insert_hmac - insert a HMAC into a UBIFS node
 * @c: UBIFS file-system description object
 * @node: the node to insert a HMAC into.
 * @len: the length of the node
 * @ofs_hmac: the offset in the node where the HMAC is inserted
 *
 * This function inserts a HMAC at offset @ofs_hmac into the node given in
 * @node.
 *
 * This function returns 0 for success or a negative error code otherwise.
 */
int __ubifs_node_insert_hmac(const struct ubifs_info *c, void *node, int len,
                            int ofs_hmac)
{
        return ubifs_node_calc_hmac(c, node, len, ofs_hmac, node + ofs_hmac);
}

/**
 * __ubifs_node_verify_hmac - verify the HMAC of UBIFS node
 * @c: UBIFS file-system description object
 * @node: the node to insert a HMAC into.
 * @len: the length of the node
 * @ofs_hmac: the offset in the node where the HMAC is inserted
 *
 * This function verifies the HMAC at offset @ofs_hmac of the node given in
 * @node. Returns 0 if successful or a negative error code otherwise.
 */
int __ubifs_node_verify_hmac(const struct ubifs_info *c, const void *node,
                             int len, int ofs_hmac)
{
        int hmac_len = c->hmac_desc_len;
        u8 *hmac;
        int err;

        hmac = kmalloc(hmac_len, GFP_NOFS);
        if (!hmac)
                return -ENOMEM;

        err = ubifs_node_calc_hmac(c, node, len, ofs_hmac, hmac);
        if (err) {
                kfree(hmac);
                return err;
        }

        err = crypto_memneq(hmac, node + ofs_hmac, hmac_len);

        kfree(hmac);

        if (!err)
                return 0;

        return -EPERM;
}

int __ubifs_shash_copy_state(const struct ubifs_info *c, struct shash_desc *src,
                             struct shash_desc *target)
{
        u8 *state;
        int err;

        state = kmalloc(crypto_shash_descsize(src->tfm), GFP_NOFS);
        if (!state)
                return -ENOMEM;

        err = crypto_shash_export(src, state);
        if (err)
                goto out;

        err = crypto_shash_import(target, state);

out:
        kfree(state);

        return err;
}

/**
 * ubifs_hmac_wkm - Create a HMAC of the well known message
 * @c: UBIFS file-system description object
 * @hmac: The HMAC of the well known message
 *
 * This function creates a HMAC of a well known message. This is used
 * to check if the provided key is suitable to authenticate a UBIFS
 * image. This is only a convenience to the user to provide a better
 * error message when the wrong key is provided.
 *
 * This function returns 0 for success or a negative error code otherwise.
 */
int ubifs_hmac_wkm(struct ubifs_info *c, u8 *hmac)
{
        SHASH_DESC_ON_STACK(shash, c->hmac_tfm);
        int err;
        const char well_known_message[] = "UBIFS";

        if (!ubifs_authenticated(c))
                return 0;

        shash->tfm = c->hmac_tfm;

        err = crypto_shash_init(shash);
        if (err)
                return err;

        err = crypto_shash_update(shash, well_known_message,
                                  sizeof(well_known_message) - 1);
        if (err < 0)
                return err;

        err = crypto_shash_final(shash, hmac);
        if (err)
                return err;
        return 0;
}

/*
 * ubifs_hmac_zero - test if a HMAC is zero
 * @c: UBIFS file-system description object
 * @hmac: the HMAC to test
 *
 * This function tests if a HMAC is zero and returns true if it is
 * and false otherwise.
 */
bool ubifs_hmac_zero(struct ubifs_info *c, const u8 *hmac)
{
        return !memchr_inv(hmac, 0, c->hmac_desc_len);
}