// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (c) 2015 Pablo Neira Ayuso <pablo@netfilter.org>
 */

#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 <linux/ip.h>
#include <linux/ipv6.h>
#include <net/netfilter/nf_tables.h>
#include <net/netfilter/nf_tables_offload.h>
#include <net/netfilter/nf_dup_netdev.h>
#include <net/neighbour.h>
#include <net/ip.h>

struct nft_fwd_netdev {
        u8      sreg_dev;
};

static void nft_fwd_netdev_eval(const struct nft_expr *expr,
                                struct nft_regs *regs,
                                const struct nft_pktinfo *pkt)
{
        struct nft_fwd_netdev *priv = nft_expr_priv(expr);
        int oif = regs->data[priv->sreg_dev];
        struct sk_buff *skb = pkt->skb;

        /* This is used by ifb only. */
        skb->skb_iif = skb->dev->ifindex;
        skb_set_redirected(skb, nft_hook(pkt) == NF_NETDEV_INGRESS);

        nf_fwd_netdev_egress(pkt, oif);
        regs->verdict.code = NF_STOLEN;
}

static const struct nla_policy nft_fwd_netdev_policy[NFTA_FWD_MAX + 1] = {
        [NFTA_FWD_SREG_DEV]     = { .type = NLA_U32 },
        [NFTA_FWD_SREG_ADDR]    = { .type = NLA_U32 },
        [NFTA_FWD_NFPROTO]      = NLA_POLICY_MAX(NLA_BE32, 255),
};

static int nft_fwd_netdev_init(const struct nft_ctx *ctx,
                               const struct nft_expr *expr,
                               const struct nlattr * const tb[])
{
        struct nft_fwd_netdev *priv = nft_expr_priv(expr);

        if (tb[NFTA_FWD_SREG_DEV] == NULL)
                return -EINVAL;

        return nft_parse_register_load(ctx, tb[NFTA_FWD_SREG_DEV], &priv->sreg_dev,
                                       sizeof(int));
}

static int nft_fwd_netdev_dump(struct sk_buff *skb,
                               const struct nft_expr *expr, bool reset)
{
        struct nft_fwd_netdev *priv = nft_expr_priv(expr);

        if (nft_dump_register(skb, NFTA_FWD_SREG_DEV, priv->sreg_dev))
                goto nla_put_failure;

        return 0;

nla_put_failure:
        return -1;
}

static int nft_fwd_netdev_offload(struct nft_offload_ctx *ctx,
                                  struct nft_flow_rule *flow,
                                  const struct nft_expr *expr)
{
        const struct nft_fwd_netdev *priv = nft_expr_priv(expr);
        int oif = ctx->regs[priv->sreg_dev].data.data[0];

        return nft_fwd_dup_netdev_offload(ctx, flow, FLOW_ACTION_REDIRECT, oif);
}

static bool nft_fwd_netdev_offload_action(const struct nft_expr *expr)
{
        return true;
}

struct nft_fwd_neigh {
        u8                      sreg_dev;
        u8                      sreg_addr;
        u8                      nfproto;
};

static void nft_fwd_neigh_eval(const struct nft_expr *expr,
                              struct nft_regs *regs,
                              const struct nft_pktinfo *pkt)
{
        struct nft_fwd_neigh *priv = nft_expr_priv(expr);
        void *addr = &regs->data[priv->sreg_addr];
        int oif = regs->data[priv->sreg_dev];
        unsigned int verdict = NF_STOLEN;
        struct sk_buff *skb = pkt->skb;
        struct net_device *dev;
        int neigh_table;

        switch (priv->nfproto) {
        case NFPROTO_IPV4: {
                struct iphdr *iph;

                if (skb->protocol != htons(ETH_P_IP)) {
                        verdict = NFT_BREAK;
                        goto out;
                }
                if (skb_try_make_writable(skb, sizeof(*iph))) {
                        verdict = NF_DROP;
                        goto out;
                }
                iph = ip_hdr(skb);
                ip_decrease_ttl(iph);
                neigh_table = NEIGH_ARP_TABLE;
                break;
                }
        case NFPROTO_IPV6: {
                struct ipv6hdr *ip6h;

                if (skb->protocol != htons(ETH_P_IPV6)) {
                        verdict = NFT_BREAK;
                        goto out;
                }
                if (skb_try_make_writable(skb, sizeof(*ip6h))) {
                        verdict = NF_DROP;
                        goto out;
                }
                ip6h = ipv6_hdr(skb);
                ip6h->hop_limit--;
                neigh_table = NEIGH_ND_TABLE;
                break;
                }
        default:
                verdict = NFT_BREAK;
                goto out;
        }

        dev = dev_get_by_index_rcu(nft_net(pkt), oif);
        if (dev == NULL)
                return;

        skb->dev = dev;
        skb_clear_tstamp(skb);
        neigh_xmit(neigh_table, dev, addr, skb);
out:
        regs->verdict.code = verdict;
}

static int nft_fwd_neigh_init(const struct nft_ctx *ctx,
                              const struct nft_expr *expr,
                              const struct nlattr * const tb[])
{
        struct nft_fwd_neigh *priv = nft_expr_priv(expr);
        unsigned int addr_len;
        int err;

        if (!tb[NFTA_FWD_SREG_DEV] ||
            !tb[NFTA_FWD_SREG_ADDR] ||
            !tb[NFTA_FWD_NFPROTO])
                return -EINVAL;

        priv->nfproto = ntohl(nla_get_be32(tb[NFTA_FWD_NFPROTO]));

        switch (priv->nfproto) {
        case NFPROTO_IPV4:
                addr_len = sizeof(struct in_addr);
                break;
        case NFPROTO_IPV6:
                addr_len = sizeof(struct in6_addr);
                break;
        default:
                return -EOPNOTSUPP;
        }

        err = nft_parse_register_load(ctx, tb[NFTA_FWD_SREG_DEV], &priv->sreg_dev,
                                      sizeof(int));
        if (err < 0)
                return err;

        return nft_parse_register_load(ctx, tb[NFTA_FWD_SREG_ADDR], &priv->sreg_addr,
                                       addr_len);
}

static int nft_fwd_neigh_dump(struct sk_buff *skb,
                              const struct nft_expr *expr, bool reset)
{
        struct nft_fwd_neigh *priv = nft_expr_priv(expr);

        if (nft_dump_register(skb, NFTA_FWD_SREG_DEV, priv->sreg_dev) ||
            nft_dump_register(skb, NFTA_FWD_SREG_ADDR, priv->sreg_addr) ||
            nla_put_be32(skb, NFTA_FWD_NFPROTO, htonl(priv->nfproto)))
                goto nla_put_failure;

        return 0;

nla_put_failure:
        return -1;
}

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

static struct nft_expr_type nft_fwd_netdev_type;
static const struct nft_expr_ops nft_fwd_neigh_netdev_ops = {
        .type           = &nft_fwd_netdev_type,
        .size           = NFT_EXPR_SIZE(sizeof(struct nft_fwd_neigh)),
        .eval           = nft_fwd_neigh_eval,
        .init           = nft_fwd_neigh_init,
        .dump           = nft_fwd_neigh_dump,
        .validate       = nft_fwd_validate,
        .reduce         = NFT_REDUCE_READONLY,
};

static const struct nft_expr_ops nft_fwd_netdev_ops = {
        .type           = &nft_fwd_netdev_type,
        .size           = NFT_EXPR_SIZE(sizeof(struct nft_fwd_netdev)),
        .eval           = nft_fwd_netdev_eval,
        .init           = nft_fwd_netdev_init,
        .dump           = nft_fwd_netdev_dump,
        .validate       = nft_fwd_validate,
        .reduce         = NFT_REDUCE_READONLY,
        .offload        = nft_fwd_netdev_offload,
        .offload_action = nft_fwd_netdev_offload_action,
};

static const struct nft_expr_ops *
nft_fwd_select_ops(const struct nft_ctx *ctx,
                   const struct nlattr * const tb[])
{
        if (tb[NFTA_FWD_SREG_ADDR])
                return &nft_fwd_neigh_netdev_ops;
        if (tb[NFTA_FWD_SREG_DEV])
                return &nft_fwd_netdev_ops;

        return ERR_PTR(-EOPNOTSUPP);
}

static struct nft_expr_type nft_fwd_netdev_type __read_mostly = {
        .family         = NFPROTO_NETDEV,
        .name           = "fwd",
        .select_ops     = nft_fwd_select_ops,
        .policy         = nft_fwd_netdev_policy,
        .maxattr        = NFTA_FWD_MAX,
        .owner          = THIS_MODULE,
};

static int __init nft_fwd_netdev_module_init(void)
{
        return nft_register_expr(&nft_fwd_netdev_type);
}

static void __exit nft_fwd_netdev_module_exit(void)
{
        nft_unregister_expr(&nft_fwd_netdev_type);
}

module_init(nft_fwd_netdev_module_init);
module_exit(nft_fwd_netdev_module_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Pablo Neira Ayuso <pablo@netfilter.org>");
MODULE_DESCRIPTION("nftables netdev packet forwarding support");
MODULE_ALIAS_NFT_AF_EXPR(5, "fwd");