// SPDX-License-Identifier: GPL-2.0-only
#include <net/ip.h>
#include <net/tcp.h>

#include <net/netfilter/nf_tables.h>
#include <linux/netfilter/nfnetlink_osf.h>

struct nft_osf {
        u8                      dreg;
        u8                      ttl;
        u32                     flags;
};

static const struct nla_policy nft_osf_policy[NFTA_OSF_MAX + 1] = {
        [NFTA_OSF_DREG]         = { .type = NLA_U32 },
        [NFTA_OSF_TTL]          = { .type = NLA_U8 },
        [NFTA_OSF_FLAGS]        = { .type = NLA_U32 },
};

static void nft_osf_eval(const struct nft_expr *expr, struct nft_regs *regs,
                         const struct nft_pktinfo *pkt)
{
        struct nft_osf *priv = nft_expr_priv(expr);
        u32 *dest = &regs->data[priv->dreg];
        struct sk_buff *skb = pkt->skb;
        char os_match[NFT_OSF_MAXGENRELEN];
        const struct tcphdr *tcp;
        struct nf_osf_data data;
        struct tcphdr _tcph;

        if (pkt->tprot != IPPROTO_TCP) {
                regs->verdict.code = NFT_BREAK;
                return;
        }

        tcp = skb_header_pointer(skb, ip_hdrlen(skb),
                                 sizeof(struct tcphdr), &_tcph);
        if (!tcp) {
                regs->verdict.code = NFT_BREAK;
                return;
        }
        if (!tcp->syn) {
                regs->verdict.code = NFT_BREAK;
                return;
        }

        if (!nf_osf_find(skb, nf_osf_fingers, priv->ttl, &data)) {
                strscpy_pad((char *)dest, "unknown", NFT_OSF_MAXGENRELEN);
        } else {
                if (priv->flags & NFT_OSF_F_VERSION)
                        snprintf(os_match, NFT_OSF_MAXGENRELEN, "%s:%s",
                                 data.genre, data.version);
                else
                        strscpy(os_match, data.genre, NFT_OSF_MAXGENRELEN);

                strscpy_pad((char *)dest, os_match, NFT_OSF_MAXGENRELEN);
        }
}

static int nft_osf_init(const struct nft_ctx *ctx,
                        const struct nft_expr *expr,
                        const struct nlattr * const tb[])
{
        struct nft_osf *priv = nft_expr_priv(expr);
        u32 flags;
        u8 ttl;

        if (!tb[NFTA_OSF_DREG])
                return -EINVAL;

        if (tb[NFTA_OSF_TTL]) {
                ttl = nla_get_u8(tb[NFTA_OSF_TTL]);
                if (ttl > 2)
                        return -EINVAL;
                priv->ttl = ttl;
        }

        if (tb[NFTA_OSF_FLAGS]) {
                flags = ntohl(nla_get_be32(tb[NFTA_OSF_FLAGS]));
                if (flags != NFT_OSF_F_VERSION)
                        return -EINVAL;
                priv->flags = flags;
        }

        return nft_parse_register_store(ctx, tb[NFTA_OSF_DREG], &priv->dreg,
                                        NULL, NFT_DATA_VALUE,
                                        NFT_OSF_MAXGENRELEN);
}

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

        if (nla_put_u8(skb, NFTA_OSF_TTL, priv->ttl))
                goto nla_put_failure;

        if (nla_put_u32(skb, NFTA_OSF_FLAGS, ntohl((__force __be32)priv->flags)))
                goto nla_put_failure;

        if (nft_dump_register(skb, NFTA_OSF_DREG, priv->dreg))
                goto nla_put_failure;

        return 0;

nla_put_failure:
        return -1;
}

static int nft_osf_validate(const struct nft_ctx *ctx,
                            const struct nft_expr *expr)
{
        unsigned int hooks;

        switch (ctx->family) {
        case NFPROTO_IPV4:
        case NFPROTO_IPV6:
        case NFPROTO_INET:
                hooks = (1 << NF_INET_LOCAL_IN) |
                        (1 << NF_INET_PRE_ROUTING) |
                        (1 << NF_INET_FORWARD);
                break;
        default:
                return -EOPNOTSUPP;
        }

        return nft_chain_validate_hooks(ctx->chain, hooks);
}

static bool nft_osf_reduce(struct nft_regs_track *track,
                           const struct nft_expr *expr)
{
        struct nft_osf *priv = nft_expr_priv(expr);
        struct nft_osf *osf;

        if (!nft_reg_track_cmp(track, expr, priv->dreg)) {
                nft_reg_track_update(track, expr, priv->dreg, NFT_OSF_MAXGENRELEN);
                return false;
        }

        osf = nft_expr_priv(track->regs[priv->dreg].selector);
        if (priv->flags != osf->flags ||
            priv->ttl != osf->ttl) {
                nft_reg_track_update(track, expr, priv->dreg, NFT_OSF_MAXGENRELEN);
                return false;
        }

        if (!track->regs[priv->dreg].bitwise)
                return true;

        return false;
}

static struct nft_expr_type nft_osf_type;
static const struct nft_expr_ops nft_osf_op = {
        .eval           = nft_osf_eval,
        .size           = NFT_EXPR_SIZE(sizeof(struct nft_osf)),
        .init           = nft_osf_init,
        .dump           = nft_osf_dump,
        .type           = &nft_osf_type,
        .validate       = nft_osf_validate,
        .reduce         = nft_osf_reduce,
};

static struct nft_expr_type nft_osf_type __read_mostly = {
        .ops            = &nft_osf_op,
        .name           = "osf",
        .owner          = THIS_MODULE,
        .policy         = nft_osf_policy,
        .maxattr        = NFTA_OSF_MAX,
};

static int __init nft_osf_module_init(void)
{
        return nft_register_expr(&nft_osf_type);
}

static void __exit nft_osf_module_exit(void)
{
        return nft_unregister_expr(&nft_osf_type);
}

module_init(nft_osf_module_init);
module_exit(nft_osf_module_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Fernando Fernandez <ffmancera@riseup.net>");
MODULE_ALIAS_NFT_EXPR("osf");
MODULE_DESCRIPTION("nftables passive OS fingerprint support");