/*
 * algif_rng: User-space interface for random number generators
 *
 * This file provides the user-space API for random number generators.
 *
 * Copyright (C) 2014, Stephan Mueller <smueller@chronox.de>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, and the entire permission notice in its entirety,
 *    including the disclaimer of warranties.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote
 *    products derived from this software without specific prior
 *    written permission.
 *
 * ALTERNATIVELY, this product may be distributed under the terms of
 * the GNU General Public License, in which case the provisions of the GPL2
 * are required INSTEAD OF the above restrictions.  (This clause is
 * necessary due to a potential bad interaction between the GPL and
 * the restrictions contained in a BSD-style copyright.)
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ALL OF
 * WHICH ARE HEREBY DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
 * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
 * USE OF THIS SOFTWARE, EVEN IF NOT ADVISED OF THE POSSIBILITY OF SUCH
 * DAMAGE.
 */

#include <linux/capability.h>
#include <linux/module.h>
#include <crypto/rng.h>
#include <linux/random.h>
#include <crypto/if_alg.h>
#include <linux/net.h>
#include <net/sock.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Stephan Mueller <smueller@chronox.de>");
MODULE_DESCRIPTION("User-space interface for random number generators");

struct rng_ctx {
#define MAXSIZE 128
        unsigned int len;
        struct crypto_rng *drng;
        u8 *addtl;
        size_t addtl_len;
};

struct rng_parent_ctx {
        struct crypto_rng *drng;
        u8 *entropy;
};

static void rng_reset_addtl(struct rng_ctx *ctx)
{
        kfree_sensitive(ctx->addtl);
        ctx->addtl = NULL;
        ctx->addtl_len = 0;
}

static int _rng_recvmsg(struct crypto_rng *drng, struct msghdr *msg, size_t len,
                        u8 *addtl, size_t addtl_len)
{
        int err = 0;
        int genlen = 0;
        u8 result[MAXSIZE];

        if (len == 0)
                return 0;
        if (len > MAXSIZE)
                len = MAXSIZE;

        /*
         * although not strictly needed, this is a precaution against coding
         * errors
         */
        memset(result, 0, len);

        /*
         * The enforcement of a proper seeding of an RNG is done within an
         * RNG implementation. Some RNGs (DRBG, krng) do not need specific
         * seeding as they automatically seed. The X9.31 DRNG will return
         * an error if it was not seeded properly.
         */
        genlen = crypto_rng_generate(drng, addtl, addtl_len, result, len);
        if (genlen < 0)
                return genlen;

        err = memcpy_to_msg(msg, result, len);
        memzero_explicit(result, len);

        return err ? err : len;
}

static int rng_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
                       int flags)
{
        struct sock *sk = sock->sk;
        struct alg_sock *ask = alg_sk(sk);
        struct rng_ctx *ctx = ask->private;

        return _rng_recvmsg(ctx->drng, msg, len, NULL, 0);
}

static int rng_test_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
                            int flags)
{
        struct sock *sk = sock->sk;
        struct alg_sock *ask = alg_sk(sk);
        struct rng_ctx *ctx = ask->private;
        int ret;

        lock_sock(sock->sk);
        ret = _rng_recvmsg(ctx->drng, msg, len, ctx->addtl, ctx->addtl_len);
        rng_reset_addtl(ctx);
        release_sock(sock->sk);

        return ret;
}

static int rng_test_sendmsg(struct socket *sock, struct msghdr *msg, size_t len)
{
        int err;
        struct alg_sock *ask = alg_sk(sock->sk);
        struct rng_ctx *ctx = ask->private;

        lock_sock(sock->sk);
        if (len > MAXSIZE) {
                err = -EMSGSIZE;
                goto unlock;
        }

        rng_reset_addtl(ctx);
        ctx->addtl = kmalloc(len, GFP_KERNEL);
        if (!ctx->addtl) {
                err = -ENOMEM;
                goto unlock;
        }

        err = memcpy_from_msg(ctx->addtl, msg, len);
        if (err) {
                rng_reset_addtl(ctx);
                goto unlock;
        }
        ctx->addtl_len = len;

unlock:
        release_sock(sock->sk);
        return err ? err : len;
}

static struct proto_ops algif_rng_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,
        .mmap           =       sock_no_mmap,
        .bind           =       sock_no_bind,
        .accept         =       sock_no_accept,
        .sendmsg        =       sock_no_sendmsg,

        .release        =       af_alg_release,
        .recvmsg        =       rng_recvmsg,
};

static struct proto_ops __maybe_unused algif_rng_test_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,
        .mmap           =       sock_no_mmap,
        .bind           =       sock_no_bind,
        .accept         =       sock_no_accept,

        .release        =       af_alg_release,
        .recvmsg        =       rng_test_recvmsg,
        .sendmsg        =       rng_test_sendmsg,
};

static void *rng_bind(const char *name, u32 type, u32 mask)
{
        struct rng_parent_ctx *pctx;
        struct crypto_rng *rng;

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

        rng = crypto_alloc_rng(name, type, mask);
        if (IS_ERR(rng)) {
                kfree(pctx);
                return ERR_CAST(rng);
        }

        pctx->drng = rng;
        return pctx;
}

static void rng_release(void *private)
{
        struct rng_parent_ctx *pctx = private;

        if (unlikely(!pctx))
                return;
        crypto_free_rng(pctx->drng);
        kfree_sensitive(pctx->entropy);
        kfree_sensitive(pctx);
}

static void rng_sock_destruct(struct sock *sk)
{
        struct alg_sock *ask = alg_sk(sk);
        struct rng_ctx *ctx = ask->private;

        rng_reset_addtl(ctx);
        sock_kfree_s(sk, ctx, ctx->len);
        af_alg_release_parent(sk);
}

static int rng_accept_parent(void *private, struct sock *sk)
{
        struct rng_ctx *ctx;
        struct rng_parent_ctx *pctx = private;
        struct alg_sock *ask = alg_sk(sk);
        unsigned int len = sizeof(*ctx);

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

        ctx->len = len;
        ctx->addtl = NULL;
        ctx->addtl_len = 0;

        /*
         * No seeding done at that point -- if multiple accepts are
         * done on one RNG instance, each resulting FD points to the same
         * state of the RNG.
         */

        ctx->drng = pctx->drng;
        ask->private = ctx;
        sk->sk_destruct = rng_sock_destruct;

        /*
         * Non NULL pctx->entropy means that CAVP test has been initiated on
         * this socket, replace proto_ops algif_rng_ops with algif_rng_test_ops.
         */
        if (IS_ENABLED(CONFIG_CRYPTO_USER_API_RNG_CAVP) && pctx->entropy)
                sk->sk_socket->ops = &algif_rng_test_ops;

        return 0;
}

static int rng_setkey(void *private, const u8 *seed, unsigned int seedlen)
{
        struct rng_parent_ctx *pctx = private;
        /*
         * Check whether seedlen is of sufficient size is done in RNG
         * implementations.
         */
        return crypto_rng_reset(pctx->drng, seed, seedlen);
}

static int __maybe_unused rng_setentropy(void *private, sockptr_t entropy,
                                         unsigned int len)
{
        struct rng_parent_ctx *pctx = private;
        u8 *kentropy = NULL;

        if (!capable(CAP_SYS_ADMIN))
                return -EACCES;

        if (pctx->entropy)
                return -EINVAL;

        if (len > MAXSIZE)
                return -EMSGSIZE;

        if (len) {
                kentropy = memdup_sockptr(entropy, len);
                if (IS_ERR(kentropy))
                        return PTR_ERR(kentropy);
        }

        crypto_rng_alg(pctx->drng)->set_ent(pctx->drng, kentropy, len);
        /*
         * Since rng doesn't perform any memory management for the entropy
         * buffer, save kentropy pointer to pctx now to free it after use.
         */
        pctx->entropy = kentropy;
        return 0;
}

static const struct af_alg_type algif_type_rng = {
        .bind           =       rng_bind,
        .release        =       rng_release,
        .accept         =       rng_accept_parent,
        .setkey         =       rng_setkey,
#ifdef CONFIG_CRYPTO_USER_API_RNG_CAVP
        .setentropy     =       rng_setentropy,
#endif
        .ops            =       &algif_rng_ops,
        .name           =       "rng",
        .owner          =       THIS_MODULE
};

static int __init rng_init(void)
{
        return af_alg_register_type(&algif_type_rng);
}

static void __exit rng_exit(void)
{
        int err = af_alg_unregister_type(&algif_type_rng);
        BUG_ON(err);
}

module_init(rng_init);
module_exit(rng_exit);