/*
 * eseqiv: Encrypted Sequence Number IV Generator
 *
 * This generator generates an IV based on a sequence number by xoring it
 * with a salt and then encrypting it with the same key as used to encrypt
 * the plain text.  This algorithm requires that the block size be equal
 * to the IV size.  It is mainly useful for CBC.
 *
 * Copyright (c) 2007 Herbert Xu <herbert@gondor.apana.org.au>
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the Free
 * Software Foundation; either version 2 of the License, or (at your option)
 * any later version.
 *
 */

#include <crypto/internal/skcipher.h>
#include <crypto/rng.h>
#include <crypto/scatterwalk.h>
#include <linux/err.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/scatterlist.h>
#include <linux/spinlock.h>
#include <linux/string.h>

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

struct eseqiv_ctx {
        spinlock_t lock;
        unsigned int reqoff;
        char salt[];
};

static void eseqiv_complete2(struct skcipher_givcrypt_request *req)
{
        struct crypto_ablkcipher *geniv = skcipher_givcrypt_reqtfm(req);
        struct eseqiv_request_ctx *reqctx = skcipher_givcrypt_reqctx(req);

        memcpy(req->giv, PTR_ALIGN((u8 *)reqctx->tail,
                         crypto_ablkcipher_alignmask(geniv) + 1),
               crypto_ablkcipher_ivsize(geniv));
}

static void eseqiv_complete(struct crypto_async_request *base, int err)
{
        struct skcipher_givcrypt_request *req = base->data;

        if (err)
                goto out;

        eseqiv_complete2(req);

out:
        skcipher_givcrypt_complete(req, err);
}

static void eseqiv_chain(struct scatterlist *head, struct scatterlist *sg,
                         int chain)
{
        if (chain) {
                head->length += sg->length;
                sg = scatterwalk_sg_next(sg);
        }

        if (sg)
                scatterwalk_sg_chain(head, 2, sg);
        else
                sg_mark_end(head);
}

static int eseqiv_givencrypt(struct skcipher_givcrypt_request *req)
{
        struct crypto_ablkcipher *geniv = skcipher_givcrypt_reqtfm(req);
        struct eseqiv_ctx *ctx = crypto_ablkcipher_ctx(geniv);
        struct eseqiv_request_ctx *reqctx = skcipher_givcrypt_reqctx(req);
        struct ablkcipher_request *subreq;
        crypto_completion_t complete;
        void *data;
        struct scatterlist *osrc, *odst;
        struct scatterlist *dst;
        struct page *srcp;
        struct page *dstp;
        u8 *giv;
        u8 *vsrc;
        u8 *vdst;
        __be64 seq;
        unsigned int ivsize;
        unsigned int len;
        int err;

        subreq = (void *)(reqctx->tail + ctx->reqoff);
        ablkcipher_request_set_tfm(subreq, skcipher_geniv_cipher(geniv));

        giv = req->giv;
        complete = req->creq.base.complete;
        data = req->creq.base.data;

        osrc = req->creq.src;
        odst = req->creq.dst;
        srcp = sg_page(osrc);
        dstp = sg_page(odst);
        vsrc = PageHighMem(srcp) ? NULL : page_address(srcp) + osrc->offset;
        vdst = PageHighMem(dstp) ? NULL : page_address(dstp) + odst->offset;

        ivsize = crypto_ablkcipher_ivsize(geniv);

        if (vsrc != giv + ivsize && vdst != giv + ivsize) {
                giv = PTR_ALIGN((u8 *)reqctx->tail,
                                crypto_ablkcipher_alignmask(geniv) + 1);
                complete = eseqiv_complete;
                data = req;
        }

        ablkcipher_request_set_callback(subreq, req->creq.base.flags, complete,
                                        data);

        sg_init_table(reqctx->src, 2);
        sg_set_buf(reqctx->src, giv, ivsize);
        eseqiv_chain(reqctx->src, osrc, vsrc == giv + ivsize);

        dst = reqctx->src;
        if (osrc != odst) {
                sg_init_table(reqctx->dst, 2);
                sg_set_buf(reqctx->dst, giv, ivsize);
                eseqiv_chain(reqctx->dst, odst, vdst == giv + ivsize);

                dst = reqctx->dst;
        }

        ablkcipher_request_set_crypt(subreq, reqctx->src, dst,
                                     req->creq.nbytes + ivsize,
                                     req->creq.info);

        memcpy(req->creq.info, ctx->salt, ivsize);

        len = ivsize;
        if (ivsize > sizeof(u64)) {
                memset(req->giv, 0, ivsize - sizeof(u64));
                len = sizeof(u64);
        }
        seq = cpu_to_be64(req->seq);
        memcpy(req->giv + ivsize - len, &seq, len);

        err = crypto_ablkcipher_encrypt(subreq);
        if (err)
                goto out;

        if (giv != req->giv)
                eseqiv_complete2(req);

out:
        return err;
}

static int eseqiv_givencrypt_first(struct skcipher_givcrypt_request *req)
{
        struct crypto_ablkcipher *geniv = skcipher_givcrypt_reqtfm(req);
        struct eseqiv_ctx *ctx = crypto_ablkcipher_ctx(geniv);
        int err = 0;

        spin_lock_bh(&ctx->lock);
        if (crypto_ablkcipher_crt(geniv)->givencrypt != eseqiv_givencrypt_first)
                goto unlock;

        crypto_ablkcipher_crt(geniv)->givencrypt = eseqiv_givencrypt;
        err = crypto_rng_get_bytes(crypto_default_rng, ctx->salt,
                                   crypto_ablkcipher_ivsize(geniv));

unlock:
        spin_unlock_bh(&ctx->lock);

        if (err)
                return err;

        return eseqiv_givencrypt(req);
}

static int eseqiv_init(struct crypto_tfm *tfm)
{
        struct crypto_ablkcipher *geniv = __crypto_ablkcipher_cast(tfm);
        struct eseqiv_ctx *ctx = crypto_ablkcipher_ctx(geniv);
        unsigned long alignmask;
        unsigned int reqsize;

        spin_lock_init(&ctx->lock);

        alignmask = crypto_tfm_ctx_alignment() - 1;
        reqsize = sizeof(struct eseqiv_request_ctx);

        if (alignmask & reqsize) {
                alignmask &= reqsize;
                alignmask--;
        }

        alignmask = ~alignmask;
        alignmask &= crypto_ablkcipher_alignmask(geniv);

        reqsize += alignmask;
        reqsize += crypto_ablkcipher_ivsize(geniv);
        reqsize = ALIGN(reqsize, crypto_tfm_ctx_alignment());

        ctx->reqoff = reqsize - sizeof(struct eseqiv_request_ctx);

        tfm->crt_ablkcipher.reqsize = reqsize +
                                      sizeof(struct ablkcipher_request);

        return skcipher_geniv_init(tfm);
}

static struct crypto_template eseqiv_tmpl;

static struct crypto_instance *eseqiv_alloc(struct rtattr **tb)
{
        struct crypto_instance *inst;
        int err;

        err = crypto_get_default_rng();
        if (err)
                return ERR_PTR(err);

        inst = skcipher_geniv_alloc(&eseqiv_tmpl, tb, 0, 0);
        if (IS_ERR(inst))
                goto put_rng;

        err = -EINVAL;
        if (inst->alg.cra_ablkcipher.ivsize != inst->alg.cra_blocksize)
                goto free_inst;

        inst->alg.cra_ablkcipher.givencrypt = eseqiv_givencrypt_first;

        inst->alg.cra_init = eseqiv_init;
        inst->alg.cra_exit = skcipher_geniv_exit;

        inst->alg.cra_ctxsize = sizeof(struct eseqiv_ctx);
        inst->alg.cra_ctxsize += inst->alg.cra_ablkcipher.ivsize;

out:
        return inst;

free_inst:
        skcipher_geniv_free(inst);
        inst = ERR_PTR(err);
put_rng:
        crypto_put_default_rng();
        goto out;
}

static void eseqiv_free(struct crypto_instance *inst)
{
        skcipher_geniv_free(inst);
        crypto_put_default_rng();
}

static struct crypto_template eseqiv_tmpl = {
        .name = "eseqiv",
        .alloc = eseqiv_alloc,
        .free = eseqiv_free,
        .module = THIS_MODULE,
};

static int __init eseqiv_module_init(void)
{
        return crypto_register_template(&eseqiv_tmpl);
}

static void __exit eseqiv_module_exit(void)
{
        crypto_unregister_template(&eseqiv_tmpl);
}

module_init(eseqiv_module_init);
module_exit(eseqiv_module_exit);

MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Encrypted Sequence Number IV Generator");