// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * AEAD wrapper for Kerberos 5 RFC3961 simplified profile.
 *
 * Copyright (C) 2025 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * Derived from authenc:
 * Copyright (c) 2007-2015 Herbert Xu <herbert@gondor.apana.org.au>
 */

#include <crypto/internal/aead.h>
#include <crypto/internal/hash.h>
#include <crypto/internal/skcipher.h>
#include <crypto/authenc.h>
#include <crypto/scatterwalk.h>
#include <linux/err.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/rtnetlink.h>
#include <linux/slab.h>
#include <linux/spinlock.h>

struct krb5enc_instance_ctx {
        struct crypto_ahash_spawn auth;
        struct crypto_skcipher_spawn enc;
        unsigned int reqoff;
};

struct krb5enc_ctx {
        struct crypto_ahash *auth;
        struct crypto_skcipher *enc;
};

struct krb5enc_request_ctx {
        struct scatterlist src[2];
        struct scatterlist dst[2];
        char tail[];
};

static void krb5enc_request_complete(struct aead_request *req, int err)
{
        if (err != -EINPROGRESS)
                aead_request_complete(req, err);
}

/**
 * crypto_krb5enc_extractkeys - Extract Ke and Ki keys from the key blob.
 * @keys: Where to put the key sizes and pointers
 * @key: Encoded key material
 * @keylen: Amount of key material
 *
 * Decode the key blob we're given.  It starts with an rtattr that indicates
 * the format and the length.  Format CRYPTO_AUTHENC_KEYA_PARAM is:
 *
 *      rtattr || __be32 enckeylen || authkey || enckey
 *
 * Note that the rtattr is in cpu-endian form, unlike enckeylen.  This must be
 * handled correctly in static testmgr data.
 */
int crypto_krb5enc_extractkeys(struct crypto_authenc_keys *keys, const u8 *key,
                               unsigned int keylen)
{
        struct rtattr *rta = (struct rtattr *)key;
        struct crypto_authenc_key_param *param;

        if (!RTA_OK(rta, keylen))
                return -EINVAL;
        if (rta->rta_type != CRYPTO_AUTHENC_KEYA_PARAM)
                return -EINVAL;

        /*
         * RTA_OK() didn't align the rtattr's payload when validating that it
         * fits in the buffer.  Yet, the keys should start on the next 4-byte
         * aligned boundary.  To avoid confusion, require that the rtattr
         * payload be exactly the param struct, which has a 4-byte aligned size.
         */
        if (RTA_PAYLOAD(rta) != sizeof(*param))
                return -EINVAL;
        BUILD_BUG_ON(sizeof(*param) % RTA_ALIGNTO);

        param = RTA_DATA(rta);
        keys->enckeylen = be32_to_cpu(param->enckeylen);

        key += rta->rta_len;
        keylen -= rta->rta_len;

        if (keylen < keys->enckeylen)
                return -EINVAL;

        keys->authkeylen = keylen - keys->enckeylen;
        keys->authkey = key;
        keys->enckey = key + keys->authkeylen;
        return 0;
}
EXPORT_SYMBOL(crypto_krb5enc_extractkeys);

static int krb5enc_setkey(struct crypto_aead *krb5enc, const u8 *key,
                          unsigned int keylen)
{
        struct crypto_authenc_keys keys;
        struct krb5enc_ctx *ctx = crypto_aead_ctx(krb5enc);
        struct crypto_skcipher *enc = ctx->enc;
        struct crypto_ahash *auth = ctx->auth;
        unsigned int flags = crypto_aead_get_flags(krb5enc);
        int err = -EINVAL;

        if (crypto_krb5enc_extractkeys(&keys, key, keylen) != 0)
                goto out;

        crypto_ahash_clear_flags(auth, CRYPTO_TFM_REQ_MASK);
        crypto_ahash_set_flags(auth, flags & CRYPTO_TFM_REQ_MASK);
        err = crypto_ahash_setkey(auth, keys.authkey, keys.authkeylen);
        if (err)
                goto out;

        crypto_skcipher_clear_flags(enc, CRYPTO_TFM_REQ_MASK);
        crypto_skcipher_set_flags(enc, flags & CRYPTO_TFM_REQ_MASK);
        err = crypto_skcipher_setkey(enc, keys.enckey, keys.enckeylen);
out:
        memzero_explicit(&keys, sizeof(keys));
        return err;
}

static void krb5enc_encrypt_done(void *data, int err)
{
        struct aead_request *req = data;

        krb5enc_request_complete(req, err);
}

/*
 * Start the encryption of the plaintext.  We skip over the associated data as
 * that only gets included in the hash.
 */
static int krb5enc_dispatch_encrypt(struct aead_request *req,
                                    unsigned int flags)
{
        struct crypto_aead *krb5enc = crypto_aead_reqtfm(req);
        struct aead_instance *inst = aead_alg_instance(krb5enc);
        struct krb5enc_ctx *ctx = crypto_aead_ctx(krb5enc);
        struct krb5enc_instance_ctx *ictx = aead_instance_ctx(inst);
        struct krb5enc_request_ctx *areq_ctx = aead_request_ctx(req);
        struct crypto_skcipher *enc = ctx->enc;
        struct skcipher_request *skreq = (void *)(areq_ctx->tail +
                                                  ictx->reqoff);
        struct scatterlist *src, *dst;

        src = scatterwalk_ffwd(areq_ctx->src, req->src, req->assoclen);
        if (req->src == req->dst)
                dst = src;
        else
                dst = scatterwalk_ffwd(areq_ctx->dst, req->dst, req->assoclen);

        skcipher_request_set_tfm(skreq, enc);
        skcipher_request_set_callback(skreq, aead_request_flags(req),
                                      krb5enc_encrypt_done, req);
        skcipher_request_set_crypt(skreq, src, dst, req->cryptlen, req->iv);

        return crypto_skcipher_encrypt(skreq);
}

/*
 * Insert the hash into the checksum field in the destination buffer directly
 * after the encrypted region.
 */
static void krb5enc_insert_checksum(struct aead_request *req, u8 *hash)
{
        struct crypto_aead *krb5enc = crypto_aead_reqtfm(req);

        scatterwalk_map_and_copy(hash, req->dst,
                                 req->assoclen + req->cryptlen,
                                 crypto_aead_authsize(krb5enc), 1);
}

/*
 * Upon completion of an asynchronous digest, transfer the hash to the checksum
 * field.
 */
static void krb5enc_encrypt_ahash_done(void *data, int err)
{
        struct aead_request *req = data;
        struct crypto_aead *krb5enc = crypto_aead_reqtfm(req);
        struct aead_instance *inst = aead_alg_instance(krb5enc);
        struct krb5enc_instance_ctx *ictx = aead_instance_ctx(inst);
        struct krb5enc_request_ctx *areq_ctx = aead_request_ctx(req);
        struct ahash_request *ahreq = (void *)(areq_ctx->tail + ictx->reqoff);

        if (err)
                return krb5enc_request_complete(req, err);

        krb5enc_insert_checksum(req, ahreq->result);

        err = krb5enc_dispatch_encrypt(req, 0);
        if (err != -EINPROGRESS)
                aead_request_complete(req, err);
}

/*
 * Start the digest of the plaintext for encryption.  In theory, this could be
 * run in parallel with the encryption, provided the src and dst buffers don't
 * overlap.
 */
static int krb5enc_dispatch_encrypt_hash(struct aead_request *req)
{
        struct crypto_aead *krb5enc = crypto_aead_reqtfm(req);
        struct aead_instance *inst = aead_alg_instance(krb5enc);
        struct krb5enc_ctx *ctx = crypto_aead_ctx(krb5enc);
        struct krb5enc_instance_ctx *ictx = aead_instance_ctx(inst);
        struct crypto_ahash *auth = ctx->auth;
        struct krb5enc_request_ctx *areq_ctx = aead_request_ctx(req);
        struct ahash_request *ahreq = (void *)(areq_ctx->tail + ictx->reqoff);
        u8 *hash = areq_ctx->tail;
        int err;

        ahash_request_set_callback(ahreq, aead_request_flags(req),
                                   krb5enc_encrypt_ahash_done, req);
        ahash_request_set_tfm(ahreq, auth);
        ahash_request_set_crypt(ahreq, req->src, hash, req->assoclen + req->cryptlen);

        err = crypto_ahash_digest(ahreq);
        if (err)
                return err;

        krb5enc_insert_checksum(req, hash);
        return 0;
}

/*
 * Process an encryption operation.  We can perform the cipher and the hash in
 * parallel, provided the src and dst buffers are separate.
 */
static int krb5enc_encrypt(struct aead_request *req)
{
        int err;

        err = krb5enc_dispatch_encrypt_hash(req);
        if (err < 0)
                return err;

        return krb5enc_dispatch_encrypt(req, aead_request_flags(req));
}

static int krb5enc_verify_hash(struct aead_request *req)
{
        struct crypto_aead *krb5enc = crypto_aead_reqtfm(req);
        struct aead_instance *inst = aead_alg_instance(krb5enc);
        struct krb5enc_instance_ctx *ictx = aead_instance_ctx(inst);
        struct krb5enc_request_ctx *areq_ctx = aead_request_ctx(req);
        struct ahash_request *ahreq = (void *)(areq_ctx->tail + ictx->reqoff);
        unsigned int authsize = crypto_aead_authsize(krb5enc);
        u8 *calc_hash = areq_ctx->tail;
        u8 *msg_hash  = areq_ctx->tail + authsize;

        scatterwalk_map_and_copy(msg_hash, req->src, ahreq->nbytes, authsize, 0);

        if (crypto_memneq(msg_hash, calc_hash, authsize))
                return -EBADMSG;
        return 0;
}

static void krb5enc_decrypt_hash_done(void *data, int err)
{
        struct aead_request *req = data;

        if (err)
                return krb5enc_request_complete(req, err);

        err = krb5enc_verify_hash(req);
        krb5enc_request_complete(req, err);
}

/*
 * Dispatch the hashing of the plaintext after we've done the decryption.
 */
static int krb5enc_dispatch_decrypt_hash(struct aead_request *req)
{
        struct crypto_aead *krb5enc = crypto_aead_reqtfm(req);
        struct aead_instance *inst = aead_alg_instance(krb5enc);
        struct krb5enc_ctx *ctx = crypto_aead_ctx(krb5enc);
        struct krb5enc_instance_ctx *ictx = aead_instance_ctx(inst);
        struct krb5enc_request_ctx *areq_ctx = aead_request_ctx(req);
        struct ahash_request *ahreq = (void *)(areq_ctx->tail + ictx->reqoff);
        struct crypto_ahash *auth = ctx->auth;
        unsigned int authsize = crypto_aead_authsize(krb5enc);
        u8 *hash = areq_ctx->tail;
        int err;

        ahash_request_set_tfm(ahreq, auth);
        ahash_request_set_crypt(ahreq, req->dst, hash,
                                req->assoclen + req->cryptlen - authsize);
        ahash_request_set_callback(ahreq, aead_request_flags(req),
                                   krb5enc_decrypt_hash_done, req);

        err = crypto_ahash_digest(ahreq);
        if (err < 0)
                return err;

        return krb5enc_verify_hash(req);
}

/*
 * Dispatch the decryption of the ciphertext.
 */
static int krb5enc_dispatch_decrypt(struct aead_request *req)
{
        struct crypto_aead *krb5enc = crypto_aead_reqtfm(req);
        struct aead_instance *inst = aead_alg_instance(krb5enc);
        struct krb5enc_ctx *ctx = crypto_aead_ctx(krb5enc);
        struct krb5enc_instance_ctx *ictx = aead_instance_ctx(inst);
        struct krb5enc_request_ctx *areq_ctx = aead_request_ctx(req);
        struct skcipher_request *skreq = (void *)(areq_ctx->tail +
                                                  ictx->reqoff);
        unsigned int authsize = crypto_aead_authsize(krb5enc);
        struct scatterlist *src, *dst;

        src = scatterwalk_ffwd(areq_ctx->src, req->src, req->assoclen);
        dst = src;

        if (req->src != req->dst)
                dst = scatterwalk_ffwd(areq_ctx->dst, req->dst, req->assoclen);

        skcipher_request_set_tfm(skreq, ctx->enc);
        skcipher_request_set_callback(skreq, aead_request_flags(req),
                                      req->base.complete, req->base.data);
        skcipher_request_set_crypt(skreq, src, dst,
                                   req->cryptlen - authsize, req->iv);

        return crypto_skcipher_decrypt(skreq);
}

static int krb5enc_decrypt(struct aead_request *req)
{
        int err;

        err = krb5enc_dispatch_decrypt(req);
        if (err < 0)
                return err;

        return krb5enc_dispatch_decrypt_hash(req);
}

static int krb5enc_init_tfm(struct crypto_aead *tfm)
{
        struct aead_instance *inst = aead_alg_instance(tfm);
        struct krb5enc_instance_ctx *ictx = aead_instance_ctx(inst);
        struct krb5enc_ctx *ctx = crypto_aead_ctx(tfm);
        struct crypto_ahash *auth;
        struct crypto_skcipher *enc;
        int err;

        auth = crypto_spawn_ahash(&ictx->auth);
        if (IS_ERR(auth))
                return PTR_ERR(auth);

        enc = crypto_spawn_skcipher(&ictx->enc);
        err = PTR_ERR(enc);
        if (IS_ERR(enc))
                goto err_free_ahash;

        ctx->auth = auth;
        ctx->enc = enc;

        crypto_aead_set_reqsize(
                tfm,
                sizeof(struct krb5enc_request_ctx) +
                ictx->reqoff + /* Space for two checksums */
                umax(sizeof(struct ahash_request) + crypto_ahash_reqsize(auth),
                     sizeof(struct skcipher_request) + crypto_skcipher_reqsize(enc)));

        return 0;

err_free_ahash:
        crypto_free_ahash(auth);
        return err;
}

static void krb5enc_exit_tfm(struct crypto_aead *tfm)
{
        struct krb5enc_ctx *ctx = crypto_aead_ctx(tfm);

        crypto_free_ahash(ctx->auth);
        crypto_free_skcipher(ctx->enc);
}

static void krb5enc_free(struct aead_instance *inst)
{
        struct krb5enc_instance_ctx *ctx = aead_instance_ctx(inst);

        crypto_drop_skcipher(&ctx->enc);
        crypto_drop_ahash(&ctx->auth);
        kfree(inst);
}

/*
 * Create an instance of a template for a specific hash and cipher pair.
 */
static int krb5enc_create(struct crypto_template *tmpl, struct rtattr **tb)
{
        struct krb5enc_instance_ctx *ictx;
        struct skcipher_alg_common *enc;
        struct hash_alg_common *auth;
        struct aead_instance *inst;
        struct crypto_alg *auth_base;
        u32 mask;
        int err;

        err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_AEAD, &mask);
        if (err) {
                pr_err("attr_type failed\n");
                return err;
        }

        inst = kzalloc(sizeof(*inst) + sizeof(*ictx), GFP_KERNEL);
        if (!inst)
                return -ENOMEM;
        ictx = aead_instance_ctx(inst);

        err = crypto_grab_ahash(&ictx->auth, aead_crypto_instance(inst),
                                crypto_attr_alg_name(tb[1]), 0, mask);
        if (err) {
                pr_err("grab ahash failed\n");
                goto err_free_inst;
        }
        auth = crypto_spawn_ahash_alg(&ictx->auth);
        auth_base = &auth->base;

        err = crypto_grab_skcipher(&ictx->enc, aead_crypto_instance(inst),
                                   crypto_attr_alg_name(tb[2]), 0, mask);
        if (err) {
                pr_err("grab skcipher failed\n");
                goto err_free_inst;
        }
        enc = crypto_spawn_skcipher_alg_common(&ictx->enc);

        ictx->reqoff = 2 * auth->digestsize;

        err = -ENAMETOOLONG;
        if (snprintf(inst->alg.base.cra_name, CRYPTO_MAX_ALG_NAME,
                     "krb5enc(%s,%s)", auth_base->cra_name,
                     enc->base.cra_name) >=
            CRYPTO_MAX_ALG_NAME)
                goto err_free_inst;

        if (snprintf(inst->alg.base.cra_driver_name, CRYPTO_MAX_ALG_NAME,
                     "krb5enc(%s,%s)", auth_base->cra_driver_name,
                     enc->base.cra_driver_name) >= CRYPTO_MAX_ALG_NAME)
                goto err_free_inst;

        inst->alg.base.cra_priority = enc->base.cra_priority * 10 +
                                      auth_base->cra_priority;
        inst->alg.base.cra_blocksize = enc->base.cra_blocksize;
        inst->alg.base.cra_alignmask = enc->base.cra_alignmask;
        inst->alg.base.cra_ctxsize = sizeof(struct krb5enc_ctx);

        inst->alg.ivsize = enc->ivsize;
        inst->alg.chunksize = enc->chunksize;
        inst->alg.maxauthsize = auth->digestsize;

        inst->alg.init = krb5enc_init_tfm;
        inst->alg.exit = krb5enc_exit_tfm;

        inst->alg.setkey = krb5enc_setkey;
        inst->alg.encrypt = krb5enc_encrypt;
        inst->alg.decrypt = krb5enc_decrypt;

        inst->free = krb5enc_free;

        err = aead_register_instance(tmpl, inst);
        if (err) {
                pr_err("ref failed\n");
                goto err_free_inst;
        }

        return 0;

err_free_inst:
        krb5enc_free(inst);
        return err;
}

static struct crypto_template crypto_krb5enc_tmpl = {
        .name = "krb5enc",
        .create = krb5enc_create,
        .module = THIS_MODULE,
};

static int __init crypto_krb5enc_module_init(void)
{
        return crypto_register_template(&crypto_krb5enc_tmpl);
}

static void __exit crypto_krb5enc_module_exit(void)
{
        crypto_unregister_template(&crypto_krb5enc_tmpl);
}

module_init(crypto_krb5enc_module_init);
module_exit(crypto_krb5enc_module_exit);

MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Simple AEAD wrapper for Kerberos 5 RFC3961");
MODULE_ALIAS_CRYPTO("krb5enc");