// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (c) 2020 Laura Garcia Liebana <nevola@gmail.com>
 * Copyright (c) 2020 Jose M. Guisado <guigom@riseup.net>
 */

#include <linux/etherdevice.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/netlink.h>
#include <linux/netfilter.h>
#include <linux/netfilter/nf_tables.h>
#include <net/netfilter/nf_tables.h>
#include <net/netfilter/nft_reject.h>
#include <net/netfilter/ipv4/nf_reject.h>
#include <net/netfilter/ipv6/nf_reject.h>

static void nft_reject_queue_xmit(struct sk_buff *nskb, struct sk_buff *oldskb)
{
        dev_hard_header(nskb, nskb->dev, ntohs(oldskb->protocol),
                        eth_hdr(oldskb)->h_source, eth_hdr(oldskb)->h_dest,
                        nskb->len);
        dev_queue_xmit(nskb);
}

static void nft_reject_netdev_send_v4_tcp_reset(struct net *net,
                                                struct sk_buff *oldskb,
                                                const struct net_device *dev,
                                                int hook)
{
        struct sk_buff *nskb;

        nskb = nf_reject_skb_v4_tcp_reset(net, oldskb, dev, hook);
        if (!nskb)
                return;

        nft_reject_queue_xmit(nskb, oldskb);
}

static void nft_reject_netdev_send_v4_unreach(struct net *net,
                                              struct sk_buff *oldskb,
                                              const struct net_device *dev,
                                              int hook, u8 code)
{
        struct sk_buff *nskb;

        nskb = nf_reject_skb_v4_unreach(net, oldskb, dev, hook, code);
        if (!nskb)
                return;

        nft_reject_queue_xmit(nskb, oldskb);
}

static void nft_reject_netdev_send_v6_tcp_reset(struct net *net,
                                                struct sk_buff *oldskb,
                                                const struct net_device *dev,
                                                int hook)
{
        struct sk_buff *nskb;

        nskb = nf_reject_skb_v6_tcp_reset(net, oldskb, dev, hook);
        if (!nskb)
                return;

        nft_reject_queue_xmit(nskb, oldskb);
}


static void nft_reject_netdev_send_v6_unreach(struct net *net,
                                              struct sk_buff *oldskb,
                                              const struct net_device *dev,
                                              int hook, u8 code)
{
        struct sk_buff *nskb;

        nskb = nf_reject_skb_v6_unreach(net, oldskb, dev, hook, code);
        if (!nskb)
                return;

        nft_reject_queue_xmit(nskb, oldskb);
}

static void nft_reject_netdev_eval(const struct nft_expr *expr,
                                   struct nft_regs *regs,
                                   const struct nft_pktinfo *pkt)
{
        struct ethhdr *eth = eth_hdr(pkt->skb);
        struct nft_reject *priv = nft_expr_priv(expr);
        const unsigned char *dest = eth->h_dest;

        if (is_broadcast_ether_addr(dest) ||
            is_multicast_ether_addr(dest))
                goto out;

        switch (eth->h_proto) {
        case htons(ETH_P_IP):
                switch (priv->type) {
                case NFT_REJECT_ICMP_UNREACH:
                        nft_reject_netdev_send_v4_unreach(nft_net(pkt), pkt->skb,
                                                          nft_in(pkt),
                                                          nft_hook(pkt),
                                                          priv->icmp_code);
                        break;
                case NFT_REJECT_TCP_RST:
                        nft_reject_netdev_send_v4_tcp_reset(nft_net(pkt), pkt->skb,
                                                            nft_in(pkt),
                                                            nft_hook(pkt));
                        break;
                case NFT_REJECT_ICMPX_UNREACH:
                        nft_reject_netdev_send_v4_unreach(nft_net(pkt), pkt->skb,
                                                          nft_in(pkt),
                                                          nft_hook(pkt),
                                                          nft_reject_icmp_code(priv->icmp_code));
                        break;
                }
                break;
        case htons(ETH_P_IPV6):
                switch (priv->type) {
                case NFT_REJECT_ICMP_UNREACH:
                        nft_reject_netdev_send_v6_unreach(nft_net(pkt), pkt->skb,
                                                          nft_in(pkt),
                                                          nft_hook(pkt),
                                                          priv->icmp_code);
                        break;
                case NFT_REJECT_TCP_RST:
                        nft_reject_netdev_send_v6_tcp_reset(nft_net(pkt), pkt->skb,
                                                            nft_in(pkt),
                                                            nft_hook(pkt));
                        break;
                case NFT_REJECT_ICMPX_UNREACH:
                        nft_reject_netdev_send_v6_unreach(nft_net(pkt), pkt->skb,
                                                          nft_in(pkt),
                                                          nft_hook(pkt),
                                                          nft_reject_icmpv6_code(priv->icmp_code));
                        break;
                }
                break;
        default:
                /* No explicit way to reject this protocol, drop it. */
                break;
        }
out:
        regs->verdict.code = NF_DROP;
}

static int nft_reject_netdev_validate(const struct nft_ctx *ctx,
                                      const struct nft_expr *expr)
{
        return nft_chain_validate_hooks(ctx->chain, (1 << NF_NETDEV_INGRESS));
}

static struct nft_expr_type nft_reject_netdev_type;
static const struct nft_expr_ops nft_reject_netdev_ops = {
        .type           = &nft_reject_netdev_type,
        .size           = NFT_EXPR_SIZE(sizeof(struct nft_reject)),
        .eval           = nft_reject_netdev_eval,
        .init           = nft_reject_init,
        .dump           = nft_reject_dump,
        .validate       = nft_reject_netdev_validate,
        .reduce         = NFT_REDUCE_READONLY,
};

static struct nft_expr_type nft_reject_netdev_type __read_mostly = {
        .family         = NFPROTO_NETDEV,
        .name           = "reject",
        .ops            = &nft_reject_netdev_ops,
        .policy         = nft_reject_policy,
        .maxattr        = NFTA_REJECT_MAX,
        .owner          = THIS_MODULE,
};

static int __init nft_reject_netdev_module_init(void)
{
        return nft_register_expr(&nft_reject_netdev_type);
}

static void __exit nft_reject_netdev_module_exit(void)
{
        nft_unregister_expr(&nft_reject_netdev_type);
}

module_init(nft_reject_netdev_module_init);
module_exit(nft_reject_netdev_module_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Laura Garcia Liebana <nevola@gmail.com>");
MODULE_AUTHOR("Jose M. Guisado <guigom@riseup.net>");
MODULE_DESCRIPTION("Reject packets from netdev via nftables");
MODULE_ALIAS_NFT_AF_EXPR(5, "reject");