/*
   * 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/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;
  };
  
  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;
  	int err = -EFAULT;
  	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_get_bytes(ctx->drng, result, len);
  	if (genlen < 0)
  		return genlen;
  
  	err = memcpy_to_msg(msg, result, len);
  	memzero_explicit(result, len);
  
  	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,
  	.getsockopt	=	sock_no_getsockopt,
  	.mmap		=	sock_no_mmap,
  	.bind		=	sock_no_bind,
  	.accept		=	sock_no_accept,
  	.setsockopt	=	sock_no_setsockopt,
  	.poll		=	sock_no_poll,
  	.sendmsg	=	sock_no_sendmsg,
  	.sendpage	=	sock_no_sendpage,
  
  	.release	=	af_alg_release,
  	.recvmsg	=	rng_recvmsg,
  };
  
  static void *rng_bind(const char *name, u32 type, u32 mask)
  {
  	return crypto_alloc_rng(name, type, mask);
  }
  
  static void rng_release(void *private)
  {
  	crypto_free_rng(private);
  }
  
  static void rng_sock_destruct(struct sock *sk)
  {
  	struct alg_sock *ask = alg_sk(sk);
  	struct rng_ctx *ctx = ask->private;
  
  	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 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;
  
  	/*
  	 * 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 = private;
  	ask->private = ctx;
  	sk->sk_destruct = rng_sock_destruct;
  
  	return 0;
  }
  
  static int rng_setkey(void *private, const u8 *seed, unsigned int seedlen)
  {
  	/*
  	 * Check whether seedlen is of sufficient size is done in RNG
  	 * implementations.
  	 */
  	return crypto_rng_reset(private, seed, seedlen);
  }
  
  static const struct af_alg_type algif_type_rng = {
  	.bind		=	rng_bind,
  	.release	=	rng_release,
  	.accept		=	rng_accept_parent,
  	.setkey		=	rng_setkey,
  	.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);