/*
 * algif_aead: User-space interface for AEAD algorithms
 *
 * Copyright (C) 2014, Stephan Mueller <smueller@chronox.de>
 *
 * This file provides the user-space API for AEAD ciphers.
 *
 * 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.
 *
 * The following concept of the memory management is used:
 *
 * The kernel maintains two SGLs, the TX SGL and the RX SGL. The TX SGL is
 * filled by user space with the data submitted via sendpage/sendmsg. Filling
 * up the TX SGL does not cause a crypto operation -- the data will only be
 * tracked by the kernel. Upon receipt of one recvmsg call, the caller must
 * provide a buffer which is tracked with the RX SGL.
 *
 * During the processing of the recvmsg operation, the cipher request is
 * allocated and prepared. As part of the recvmsg operation, the processed
 * TX buffers are extracted from the TX SGL into a separate SGL.
 *
 * After the completion of the crypto operation, the RX SGL and the cipher
 * request is released. The extracted TX SGL parts are released together with
 * the RX SGL release.
 */

#include <crypto/internal/aead.h>
#include <crypto/scatterwalk.h>
#include <crypto/if_alg.h>
#include <crypto/skcipher.h>
#include <crypto/null.h>
#include <linux/init.h>
#include <linux/list.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/net.h>
#include <net/sock.h>

struct aead_tfm {
        struct crypto_aead *aead;
        struct crypto_skcipher *null_tfm;
};

static inline bool aead_sufficient_data(struct sock *sk)
{
        struct alg_sock *ask = alg_sk(sk);
        struct sock *psk = ask->parent;
        struct alg_sock *pask = alg_sk(psk);
        struct af_alg_ctx *ctx = ask->private;
        struct aead_tfm *aeadc = pask->private;
        struct crypto_aead *tfm = aeadc->aead;
        unsigned int as = crypto_aead_authsize(tfm);

        /*
         * The minimum amount of memory needed for an AEAD cipher is
         * the AAD and in case of decryption the tag.
         */
        return ctx->used >= ctx->aead_assoclen + (ctx->enc ? 0 : as);
}

static int aead_sendmsg(struct socket *sock, struct msghdr *msg, size_t size)
{
        struct sock *sk = sock->sk;
        struct alg_sock *ask = alg_sk(sk);
        struct sock *psk = ask->parent;
        struct alg_sock *pask = alg_sk(psk);
        struct aead_tfm *aeadc = pask->private;
        struct crypto_aead *tfm = aeadc->aead;
        unsigned int ivsize = crypto_aead_ivsize(tfm);

        return af_alg_sendmsg(sock, msg, size, ivsize);
}

static int crypto_aead_copy_sgl(struct crypto_skcipher *null_tfm,
                                struct scatterlist *src,
                                struct scatterlist *dst, unsigned int len)
{
        SKCIPHER_REQUEST_ON_STACK(skreq, null_tfm);

        skcipher_request_set_tfm(skreq, null_tfm);
        skcipher_request_set_callback(skreq, CRYPTO_TFM_REQ_MAY_BACKLOG,
                                      NULL, NULL);
        skcipher_request_set_crypt(skreq, src, dst, len, NULL);

        return crypto_skcipher_encrypt(skreq);
}

static int _aead_recvmsg(struct socket *sock, struct msghdr *msg,
                         size_t ignored, int flags)
{
        struct sock *sk = sock->sk;
        struct alg_sock *ask = alg_sk(sk);
        struct sock *psk = ask->parent;
        struct alg_sock *pask = alg_sk(psk);
        struct af_alg_ctx *ctx = ask->private;
        struct aead_tfm *aeadc = pask->private;
        struct crypto_aead *tfm = aeadc->aead;
        struct crypto_skcipher *null_tfm = aeadc->null_tfm;
        unsigned int i, as = crypto_aead_authsize(tfm);
        struct af_alg_async_req *areq;
        struct af_alg_tsgl *tsgl, *tmp;
        struct scatterlist *rsgl_src, *tsgl_src = NULL;
        int err = 0;
        size_t used = 0;                /* [in]  TX bufs to be en/decrypted */
        size_t outlen = 0;              /* [out] RX bufs produced by kernel */
        size_t usedpages = 0;           /* [in]  RX bufs to be used from user */
        size_t processed = 0;           /* [in]  TX bufs to be consumed */

        if (!ctx->used) {
                err = af_alg_wait_for_data(sk, flags);
                if (err)
                        return err;
        }

        /*
         * Data length provided by caller via sendmsg/sendpage that has not
         * yet been processed.
         */
        used = ctx->used;

        /*
         * Make sure sufficient data is present -- note, the same check is
         * is also present in sendmsg/sendpage. The checks in sendpage/sendmsg
         * shall provide an information to the data sender that something is
         * wrong, but they are irrelevant to maintain the kernel integrity.
         * We need this check here too in case user space decides to not honor
         * the error message in sendmsg/sendpage and still call recvmsg. This
         * check here protects the kernel integrity.
         */
        if (!aead_sufficient_data(sk))
                return -EINVAL;

        /*
         * Calculate the minimum output buffer size holding the result of the
         * cipher operation. When encrypting data, the receiving buffer is
         * larger by the tag length compared to the input buffer as the
         * encryption operation generates the tag. For decryption, the input
         * buffer provides the tag which is consumed resulting in only the
         * plaintext without a buffer for the tag returned to the caller.
         */
        if (ctx->enc)
                outlen = used + as;
        else
                outlen = used - as;

        /*
         * The cipher operation input data is reduced by the associated data
         * length as this data is processed separately later on.
         */
        used -= ctx->aead_assoclen;

        /* Allocate cipher request for current operation. */
        areq = af_alg_alloc_areq(sk, sizeof(struct af_alg_async_req) +
                                     crypto_aead_reqsize(tfm));
        if (IS_ERR(areq))
                return PTR_ERR(areq);

        /* convert iovecs of output buffers into RX SGL */
        err = af_alg_get_rsgl(sk, msg, flags, areq, outlen, &usedpages);
        if (err)
                goto free;

        /*
         * Ensure output buffer is sufficiently large. If the caller provides
         * less buffer space, only use the relative required input size. This
         * allows AIO operation where the caller sent all data to be processed
         * and the AIO operation performs the operation on the different chunks
         * of the input data.
         */
        if (usedpages < outlen) {
                size_t less = outlen - usedpages;

                if (used < less) {
                        err = -EINVAL;
                        goto free;
                }
                used -= less;
                outlen -= less;
        }

        processed = used + ctx->aead_assoclen;
        list_for_each_entry_safe(tsgl, tmp, &ctx->tsgl_list, list) {
                for (i = 0; i < tsgl->cur; i++) {
                        struct scatterlist *process_sg = tsgl->sg + i;

                        if (!(process_sg->length) || !sg_page(process_sg))
                                continue;
                        tsgl_src = process_sg;
                        break;
                }
                if (tsgl_src)
                        break;
        }
        if (processed && !tsgl_src) {
                err = -EFAULT;
                goto free;
        }

        /*
         * Copy of AAD from source to destination
         *
         * The AAD is copied to the destination buffer without change. Even
         * when user space uses an in-place cipher operation, the kernel
         * will copy the data as it does not see whether such in-place operation
         * is initiated.
         *
         * To ensure efficiency, the following implementation ensure that the
         * ciphers are invoked to perform a crypto operation in-place. This
         * is achieved by memory management specified as follows.
         */

        /* Use the RX SGL as source (and destination) for crypto op. */
        rsgl_src = areq->first_rsgl.sgl.sg;

        if (ctx->enc) {
                /*
                 * Encryption operation - The in-place cipher operation is
                 * achieved by the following operation:
                 *
                 * TX SGL: AAD || PT
                 *          |      |
                 *          | copy |
                 *          v      v
                 * RX SGL: AAD || PT || Tag
                 */
                err = crypto_aead_copy_sgl(null_tfm, tsgl_src,
                                           areq->first_rsgl.sgl.sg, processed);
                if (err)
                        goto free;
                af_alg_pull_tsgl(sk, processed, NULL, 0);
        } else {
                /*
                 * Decryption operation - To achieve an in-place cipher
                 * operation, the following  SGL structure is used:
                 *
                 * TX SGL: AAD || CT || Tag
                 *          |      |     ^
                 *          | copy |     | Create SGL link.
                 *          v      v     |
                 * RX SGL: AAD || CT ----+
                 */

                 /* Copy AAD || CT to RX SGL buffer for in-place operation. */
                err = crypto_aead_copy_sgl(null_tfm, tsgl_src,
                                           areq->first_rsgl.sgl.sg, outlen);
                if (err)
                        goto free;

                /* Create TX SGL for tag and chain it to RX SGL. */
                areq->tsgl_entries = af_alg_count_tsgl(sk, processed,
                                                       processed - as);
                if (!areq->tsgl_entries)
                        areq->tsgl_entries = 1;
                areq->tsgl = sock_kmalloc(sk, sizeof(*areq->tsgl) *
                                              areq->tsgl_entries,
                                          GFP_KERNEL);
                if (!areq->tsgl) {
                        err = -ENOMEM;
                        goto free;
                }
                sg_init_table(areq->tsgl, areq->tsgl_entries);

                /* Release TX SGL, except for tag data and reassign tag data. */
                af_alg_pull_tsgl(sk, processed, areq->tsgl, processed - as);

                /* chain the areq TX SGL holding the tag with RX SGL */
                if (usedpages) {
                        /* RX SGL present */
                        struct af_alg_sgl *sgl_prev = &areq->last_rsgl->sgl;

                        sg_unmark_end(sgl_prev->sg + sgl_prev->npages - 1);
                        sg_chain(sgl_prev->sg, sgl_prev->npages + 1,
                                 areq->tsgl);
                } else
                        /* no RX SGL present (e.g. authentication only) */
                        rsgl_src = areq->tsgl;
        }

        /* Initialize the crypto operation */
        aead_request_set_crypt(&areq->cra_u.aead_req, rsgl_src,
                               areq->first_rsgl.sgl.sg, used, ctx->iv);
        aead_request_set_ad(&areq->cra_u.aead_req, ctx->aead_assoclen);
        aead_request_set_tfm(&areq->cra_u.aead_req, tfm);

        if (msg->msg_iocb && !is_sync_kiocb(msg->msg_iocb)) {
                /* AIO operation */
                sock_hold(sk);
                areq->iocb = msg->msg_iocb;

                /* Remember output size that will be generated. */
                areq->outlen = outlen;

                aead_request_set_callback(&areq->cra_u.aead_req,
                                          CRYPTO_TFM_REQ_MAY_BACKLOG,
                                          af_alg_async_cb, areq);
                err = ctx->enc ? crypto_aead_encrypt(&areq->cra_u.aead_req) :
                                 crypto_aead_decrypt(&areq->cra_u.aead_req);

                /* AIO operation in progress */
                if (err == -EINPROGRESS || err == -EBUSY)
                        return -EIOCBQUEUED;

                sock_put(sk);
        } else {
                /* Synchronous operation */
                aead_request_set_callback(&areq->cra_u.aead_req,
                                          CRYPTO_TFM_REQ_MAY_BACKLOG,
                                          crypto_req_done, &ctx->wait);
                err = crypto_wait_req(ctx->enc ?
                                crypto_aead_encrypt(&areq->cra_u.aead_req) :
                                crypto_aead_decrypt(&areq->cra_u.aead_req),
                                &ctx->wait);
        }


free:
        af_alg_free_resources(areq);

        return err ? err : outlen;
}

static int aead_recvmsg(struct socket *sock, struct msghdr *msg,
                        size_t ignored, int flags)
{
        struct sock *sk = sock->sk;
        int ret = 0;

        lock_sock(sk);
        while (msg_data_left(msg)) {
                int err = _aead_recvmsg(sock, msg, ignored, flags);

                /*
                 * This error covers -EIOCBQUEUED which implies that we can
                 * only handle one AIO request. If the caller wants to have
                 * multiple AIO requests in parallel, he must make multiple
                 * separate AIO calls.
                 *
                 * Also return the error if no data has been processed so far.
                 */
                if (err <= 0) {
                        if (err == -EIOCBQUEUED || err == -EBADMSG || !ret)
                                ret = err;
                        goto out;
                }

                ret += err;
        }

out:
        af_alg_wmem_wakeup(sk);
        release_sock(sk);
        return ret;
}

static struct proto_ops algif_aead_ops = {
        .family         =       PF_ALG,

        .connect        =       sock_no_connect,
        .socketpair     =       sock_no_socketpair,
        .getname        =       sock_no_getname,
        .ioctl          =       sock_no_ioctl,
        .listen         =       sock_no_listen,
        .shutdown       =       sock_no_shutdown,
        .getsockopt     =       sock_no_getsockopt,
        .mmap           =       sock_no_mmap,
        .bind           =       sock_no_bind,
        .accept         =       sock_no_accept,
        .setsockopt     =       sock_no_setsockopt,

        .release        =       af_alg_release,
        .sendmsg        =       aead_sendmsg,
        .sendpage       =       af_alg_sendpage,
        .recvmsg        =       aead_recvmsg,
        .poll           =       af_alg_poll,
};

static int aead_check_key(struct socket *sock)
{
        int err = 0;
        struct sock *psk;
        struct alg_sock *pask;
        struct aead_tfm *tfm;
        struct sock *sk = sock->sk;
        struct alg_sock *ask = alg_sk(sk);

        lock_sock(sk);
        if (ask->refcnt)
                goto unlock_child;

        psk = ask->parent;
        pask = alg_sk(ask->parent);
        tfm = pask->private;

        err = -ENOKEY;
        lock_sock_nested(psk, SINGLE_DEPTH_NESTING);
        if (crypto_aead_get_flags(tfm->aead) & CRYPTO_TFM_NEED_KEY)
                goto unlock;

        if (!pask->refcnt++)
                sock_hold(psk);

        ask->refcnt = 1;
        sock_put(psk);

        err = 0;

unlock:
        release_sock(psk);
unlock_child:
        release_sock(sk);

        return err;
}

static int aead_sendmsg_nokey(struct socket *sock, struct msghdr *msg,
                                  size_t size)
{
        int err;

        err = aead_check_key(sock);
        if (err)
                return err;

        return aead_sendmsg(sock, msg, size);
}

static ssize_t aead_sendpage_nokey(struct socket *sock, struct page *page,
                                       int offset, size_t size, int flags)
{
        int err;

        err = aead_check_key(sock);
        if (err)
                return err;

        return af_alg_sendpage(sock, page, offset, size, flags);
}

static int aead_recvmsg_nokey(struct socket *sock, struct msghdr *msg,
                                  size_t ignored, int flags)
{
        int err;

        err = aead_check_key(sock);
        if (err)
                return err;

        return aead_recvmsg(sock, msg, ignored, flags);
}

static struct proto_ops algif_aead_ops_nokey = {
        .family         =       PF_ALG,

        .connect        =       sock_no_connect,
        .socketpair     =       sock_no_socketpair,
        .getname        =       sock_no_getname,
        .ioctl          =       sock_no_ioctl,
        .listen         =       sock_no_listen,
        .shutdown       =       sock_no_shutdown,
        .getsockopt     =       sock_no_getsockopt,
        .mmap           =       sock_no_mmap,
        .bind           =       sock_no_bind,
        .accept         =       sock_no_accept,
        .setsockopt     =       sock_no_setsockopt,

        .release        =       af_alg_release,
        .sendmsg        =       aead_sendmsg_nokey,
        .sendpage       =       aead_sendpage_nokey,
        .recvmsg        =       aead_recvmsg_nokey,
        .poll           =       af_alg_poll,
};

static void *aead_bind(const char *name, u32 type, u32 mask)
{
        struct aead_tfm *tfm;
        struct crypto_aead *aead;
        struct crypto_skcipher *null_tfm;

        tfm = kzalloc(sizeof(*tfm), GFP_KERNEL);
        if (!tfm)
                return ERR_PTR(-ENOMEM);

        aead = crypto_alloc_aead(name, type, mask);
        if (IS_ERR(aead)) {
                kfree(tfm);
                return ERR_CAST(aead);
        }

        null_tfm = crypto_get_default_null_skcipher();
        if (IS_ERR(null_tfm)) {
                crypto_free_aead(aead);
                kfree(tfm);
                return ERR_CAST(null_tfm);
        }

        tfm->aead = aead;
        tfm->null_tfm = null_tfm;

        return tfm;
}

static void aead_release(void *private)
{
        struct aead_tfm *tfm = private;

        crypto_free_aead(tfm->aead);
        crypto_put_default_null_skcipher();
        kfree(tfm);
}

static int aead_setauthsize(void *private, unsigned int authsize)
{
        struct aead_tfm *tfm = private;

        return crypto_aead_setauthsize(tfm->aead, authsize);
}

static int aead_setkey(void *private, const u8 *key, unsigned int keylen)
{
        struct aead_tfm *tfm = private;

        return crypto_aead_setkey(tfm->aead, key, keylen);
}

static void aead_sock_destruct(struct sock *sk)
{
        struct alg_sock *ask = alg_sk(sk);
        struct af_alg_ctx *ctx = ask->private;
        struct sock *psk = ask->parent;
        struct alg_sock *pask = alg_sk(psk);
        struct aead_tfm *aeadc = pask->private;
        struct crypto_aead *tfm = aeadc->aead;
        unsigned int ivlen = crypto_aead_ivsize(tfm);

        af_alg_pull_tsgl(sk, ctx->used, NULL, 0);
        sock_kzfree_s(sk, ctx->iv, ivlen);
        sock_kfree_s(sk, ctx, ctx->len);
        af_alg_release_parent(sk);
}

static int aead_accept_parent_nokey(void *private, struct sock *sk)
{
        struct af_alg_ctx *ctx;
        struct alg_sock *ask = alg_sk(sk);
        struct aead_tfm *tfm = private;
        struct crypto_aead *aead = tfm->aead;
        unsigned int len = sizeof(*ctx);
        unsigned int ivlen = crypto_aead_ivsize(aead);

        ctx = sock_kmalloc(sk, len, GFP_KERNEL);
        if (!ctx)
                return -ENOMEM;
        memset(ctx, 0, len);

        ctx->iv = sock_kmalloc(sk, ivlen, GFP_KERNEL);
        if (!ctx->iv) {
                sock_kfree_s(sk, ctx, len);
                return -ENOMEM;
        }
        memset(ctx->iv, 0, ivlen);

        INIT_LIST_HEAD(&ctx->tsgl_list);
        ctx->len = len;
        ctx->used = 0;
        atomic_set(&ctx->rcvused, 0);
        ctx->more = 0;
        ctx->merge = 0;
        ctx->enc = 0;
        ctx->aead_assoclen = 0;
        crypto_init_wait(&ctx->wait);

        ask->private = ctx;

        sk->sk_destruct = aead_sock_destruct;

        return 0;
}

static int aead_accept_parent(void *private, struct sock *sk)
{
        struct aead_tfm *tfm = private;

        if (crypto_aead_get_flags(tfm->aead) & CRYPTO_TFM_NEED_KEY)
                return -ENOKEY;

        return aead_accept_parent_nokey(private, sk);
}

static const struct af_alg_type algif_type_aead = {
        .bind           =       aead_bind,
        .release        =       aead_release,
        .setkey         =       aead_setkey,
        .setauthsize    =       aead_setauthsize,
        .accept         =       aead_accept_parent,
        .accept_nokey   =       aead_accept_parent_nokey,
        .ops            =       &algif_aead_ops,
        .ops_nokey      =       &algif_aead_ops_nokey,
        .name           =       "aead",
        .owner          =       THIS_MODULE
};

static int __init algif_aead_init(void)
{
        return af_alg_register_type(&algif_type_aead);
}

static void __exit algif_aead_exit(void)
{
        int err = af_alg_unregister_type(&algif_type_aead);
        BUG_ON(err);
}

module_init(algif_aead_init);
module_exit(algif_aead_exit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Stephan Mueller <smueller@chronox.de>");
MODULE_DESCRIPTION("AEAD kernel crypto API user space interface");