// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * DECnet       An implementation of the DECnet protocol suite for the LINUX
 *              operating system.  DECnet is implemented using the  BSD Socket
 *              interface as the means of communication with the user level.
 *
 *              DECnet Routing Message Grabulator
 *
 *              (C) 2000 ChyGwyn Limited  -  https://www.chygwyn.com/
 *
 * Author:      Steven Whitehouse <steve@chygwyn.com>
 */
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/netdevice.h>
#include <linux/netfilter.h>
#include <linux/spinlock.h>
#include <net/netlink.h>
#include <linux/netfilter_decnet.h>

#include <net/sock.h>
#include <net/flow.h>
#include <net/dn.h>
#include <net/dn_route.h>

static struct sock *dnrmg = NULL;


static struct sk_buff *dnrmg_build_message(struct sk_buff *rt_skb, int *errp)
{
	struct sk_buff *skb = NULL;
	size_t size;
	sk_buff_data_t old_tail;
	struct nlmsghdr *nlh;
	unsigned char *ptr;
	struct nf_dn_rtmsg *rtm;

	size = NLMSG_ALIGN(rt_skb->len) +
	       NLMSG_ALIGN(sizeof(struct nf_dn_rtmsg));
	skb = nlmsg_new(size, GFP_ATOMIC);
	if (!skb) {
		*errp = -ENOMEM;
		return NULL;
	}
	old_tail = skb->tail;
	nlh = nlmsg_put(skb, 0, 0, 0, size, 0);
	if (!nlh) {
		kfree_skb(skb);
		*errp = -ENOMEM;
		return NULL;
	}
	rtm = (struct nf_dn_rtmsg *)nlmsg_data(nlh);
	rtm->nfdn_ifindex = rt_skb->dev->ifindex;
	ptr = NFDN_RTMSG(rtm);
	skb_copy_from_linear_data(rt_skb, ptr, rt_skb->len);
	nlh->nlmsg_len = skb->tail - old_tail;
	return skb;
}

static void dnrmg_send_peer(struct sk_buff *skb)
{
	struct sk_buff *skb2;
	int status = 0;
	int group = 0;
	unsigned char flags = *skb->data;

	switch (flags & DN_RT_CNTL_MSK) {
	case DN_RT_PKT_L1RT:
		group = DNRNG_NLGRP_L1;
		break;
	case DN_RT_PKT_L2RT:
		group = DNRNG_NLGRP_L2;
		break;
	default:
		return;
	}

	skb2 = dnrmg_build_message(skb, &status);
	if (skb2 == NULL)
		return;
	NETLINK_CB(skb2).dst_group = group;
	netlink_broadcast(dnrmg, skb2, 0, group, GFP_ATOMIC);
}


static unsigned int dnrmg_hook(void *priv,
			struct sk_buff *skb,
			const struct nf_hook_state *state)
{
	dnrmg_send_peer(skb);
	return NF_ACCEPT;
}


#define RCV_SKB_FAIL(err) do { netlink_ack(skb, nlh, (err), NULL); return; } while (0)

static inline void dnrmg_receive_user_skb(struct sk_buff *skb)
{
	struct nlmsghdr *nlh = nlmsg_hdr(skb);

	if (skb->len < sizeof(*nlh) ||
	    nlh->nlmsg_len < sizeof(*nlh) ||
	    skb->len < nlh->nlmsg_len)
		return;

	if (!netlink_capable(skb, CAP_NET_ADMIN))
		RCV_SKB_FAIL(-EPERM);

	/* Eventually we might send routing messages too */

	RCV_SKB_FAIL(-EINVAL);
}

static const struct nf_hook_ops dnrmg_ops = {
	.hook		= dnrmg_hook,
	.pf		= NFPROTO_DECNET,
	.hooknum	= NF_DN_ROUTE,
	.priority	= NF_DN_PRI_DNRTMSG,
};

static int __init dn_rtmsg_init(void)
{
	int rv = 0;
	struct netlink_kernel_cfg cfg = {
		.groups	= DNRNG_NLGRP_MAX,
		.input	= dnrmg_receive_user_skb,
	};

	dnrmg = netlink_kernel_create(&init_net, NETLINK_DNRTMSG, &cfg);
	if (dnrmg == NULL) {
		printk(KERN_ERR "dn_rtmsg: Cannot create netlink socket");
		return -ENOMEM;
	}

	rv = nf_register_net_hook(&init_net, &dnrmg_ops);
	if (rv) {
		netlink_kernel_release(dnrmg);
	}

	return rv;
}

static void __exit dn_rtmsg_fini(void)
{
	nf_unregister_net_hook(&init_net, &dnrmg_ops);
	netlink_kernel_release(dnrmg);
}


MODULE_DESCRIPTION("DECnet Routing Message Grabulator");
MODULE_AUTHOR("Steven Whitehouse <steve@chygwyn.com>");
MODULE_LICENSE("GPL");
MODULE_ALIAS_NET_PF_PROTO(PF_NETLINK, NETLINK_DNRTMSG);

module_init(dn_rtmsg_init);
module_exit(dn_rtmsg_fini);