// SPDX-License-Identifier: GPL-2.0-only
#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_core.h>
#include <net/netfilter/nf_tables.h>

struct nft_last {
        unsigned long   jiffies;
        unsigned int    set;
};

struct nft_last_priv {
        struct nft_last *last;
};

static const struct nla_policy nft_last_policy[NFTA_LAST_MAX + 1] = {
        [NFTA_LAST_SET] = { .type = NLA_U32 },
        [NFTA_LAST_MSECS] = { .type = NLA_U64 },
};

static int nft_last_init(const struct nft_ctx *ctx, const struct nft_expr *expr,
                         const struct nlattr * const tb[])
{
        struct nft_last_priv *priv = nft_expr_priv(expr);
        struct nft_last *last;
        u64 last_jiffies;
        int err;

        last = kzalloc_obj(*last, GFP_KERNEL_ACCOUNT);
        if (!last)
                return -ENOMEM;

        if (tb[NFTA_LAST_SET])
                last->set = ntohl(nla_get_be32(tb[NFTA_LAST_SET]));

        if (last->set && tb[NFTA_LAST_MSECS]) {
                err = nf_msecs_to_jiffies64(tb[NFTA_LAST_MSECS], &last_jiffies);
                if (err < 0)
                        goto err;

                last->jiffies = jiffies - (unsigned long)last_jiffies;
        }
        priv->last = last;

        return 0;
err:
        kfree(last);

        return err;
}

static void nft_last_eval(const struct nft_expr *expr,
                          struct nft_regs *regs, const struct nft_pktinfo *pkt)
{
        struct nft_last_priv *priv = nft_expr_priv(expr);
        struct nft_last *last = priv->last;

        if (READ_ONCE(last->jiffies) != jiffies)
                WRITE_ONCE(last->jiffies, jiffies);
        if (READ_ONCE(last->set) == 0)
                WRITE_ONCE(last->set, 1);
}

static int nft_last_dump(struct sk_buff *skb,
                         const struct nft_expr *expr, bool reset)
{
        struct nft_last_priv *priv = nft_expr_priv(expr);
        struct nft_last *last = priv->last;
        unsigned long last_jiffies = READ_ONCE(last->jiffies);
        u32 last_set = READ_ONCE(last->set);
        __be64 msecs;

        if (time_before(jiffies, last_jiffies)) {
                WRITE_ONCE(last->set, 0);
                last_set = 0;
        }

        if (last_set)
                msecs = nf_jiffies64_to_msecs(jiffies - last_jiffies);
        else
                msecs = 0;

        if (nla_put_be32(skb, NFTA_LAST_SET, htonl(last_set)) ||
            nla_put_be64(skb, NFTA_LAST_MSECS, msecs, NFTA_LAST_PAD))
                goto nla_put_failure;

        return 0;

nla_put_failure:
        return -1;
}

static void nft_last_destroy(const struct nft_ctx *ctx,
                             const struct nft_expr *expr)
{
        struct nft_last_priv *priv = nft_expr_priv(expr);

        kfree(priv->last);
}

static int nft_last_clone(struct nft_expr *dst, const struct nft_expr *src, gfp_t gfp)
{
        struct nft_last_priv *priv_dst = nft_expr_priv(dst);
        struct nft_last_priv *priv_src = nft_expr_priv(src);

        priv_dst->last = kzalloc_obj(*priv_dst->last, gfp);
        if (!priv_dst->last)
                return -ENOMEM;

        priv_dst->last->set = priv_src->last->set;
        priv_dst->last->jiffies = priv_src->last->jiffies;

        return 0;
}

static const struct nft_expr_ops nft_last_ops = {
        .type           = &nft_last_type,
        .size           = NFT_EXPR_SIZE(sizeof(struct nft_last_priv)),
        .eval           = nft_last_eval,
        .init           = nft_last_init,
        .destroy        = nft_last_destroy,
        .clone          = nft_last_clone,
        .dump           = nft_last_dump,
        .reduce         = NFT_REDUCE_READONLY,
};

struct nft_expr_type nft_last_type __read_mostly = {
        .name           = "last",
        .ops            = &nft_last_ops,
        .policy         = nft_last_policy,
        .maxattr        = NFTA_LAST_MAX,
        .flags          = NFT_EXPR_STATEFUL,
        .owner          = THIS_MODULE,
};