// SPDX-License-Identifier: GPL-2.0
#include <linux/types.h>
#include <net/ip.h>
#include <net/tcp.h>
#include <net/netlink.h>
#include <net/netfilter/nf_tables.h>
#include <net/netfilter/nf_conntrack.h>
#include <net/netfilter/nf_conntrack_synproxy.h>
#include <net/netfilter/nf_synproxy.h>
#include <linux/netfilter_ipv4.h>
#include <linux/netfilter/nf_tables.h>
#include <linux/netfilter/nf_synproxy.h>

struct nft_synproxy {
        struct nf_synproxy_info info;
};

static const struct nla_policy nft_synproxy_policy[NFTA_SYNPROXY_MAX + 1] = {
        [NFTA_SYNPROXY_MSS]             = { .type = NLA_U16 },
        [NFTA_SYNPROXY_WSCALE]          = { .type = NLA_U8 },
        [NFTA_SYNPROXY_FLAGS]           = { .type = NLA_U32 },
};

static void nft_synproxy_tcp_options(struct synproxy_options *opts,
                                     const struct tcphdr *tcp,
                                     struct synproxy_net *snet,
                                     struct nf_synproxy_info *info,
                                     const struct nft_synproxy *priv)
{
        this_cpu_inc(snet->stats->syn_received);
        if (tcp->ece && tcp->cwr)
                opts->options |= NF_SYNPROXY_OPT_ECN;

        opts->options &= priv->info.options;
        opts->mss_encode = opts->mss_option;
        opts->mss_option = info->mss;
        if (opts->options & NF_SYNPROXY_OPT_TIMESTAMP)
                synproxy_init_timestamp_cookie(info, opts);
        else
                opts->options &= ~(NF_SYNPROXY_OPT_WSCALE |
                                   NF_SYNPROXY_OPT_SACK_PERM |
                                   NF_SYNPROXY_OPT_ECN);
}

static void nft_synproxy_eval_v4(const struct nft_synproxy *priv,
                                 struct nft_regs *regs,
                                 const struct nft_pktinfo *pkt,
                                 const struct tcphdr *tcp,
                                 struct tcphdr *_tcph,
                                 struct synproxy_options *opts)
{
        struct nf_synproxy_info info = READ_ONCE(priv->info);
        struct net *net = nft_net(pkt);
        struct synproxy_net *snet = synproxy_pernet(net);
        struct sk_buff *skb = pkt->skb;

        if (tcp->syn) {
                /* Initial SYN from client */
                nft_synproxy_tcp_options(opts, tcp, snet, &info, priv);
                synproxy_send_client_synack(net, skb, tcp, opts);
                consume_skb(skb);
                regs->verdict.code = NF_STOLEN;
        } else if (tcp->ack) {
                /* ACK from client */
                if (synproxy_recv_client_ack(net, skb, tcp, opts,
                                             ntohl(tcp->seq))) {
                        consume_skb(skb);
                        regs->verdict.code = NF_STOLEN;
                } else {
                        regs->verdict.code = NF_DROP;
                }
        }
}

#if IS_ENABLED(CONFIG_NF_TABLES_IPV6)
static void nft_synproxy_eval_v6(const struct nft_synproxy *priv,
                                 struct nft_regs *regs,
                                 const struct nft_pktinfo *pkt,
                                 const struct tcphdr *tcp,
                                 struct tcphdr *_tcph,
                                 struct synproxy_options *opts)
{
        struct nf_synproxy_info info = READ_ONCE(priv->info);
        struct net *net = nft_net(pkt);
        struct synproxy_net *snet = synproxy_pernet(net);
        struct sk_buff *skb = pkt->skb;

        if (tcp->syn) {
                /* Initial SYN from client */
                nft_synproxy_tcp_options(opts, tcp, snet, &info, priv);
                synproxy_send_client_synack_ipv6(net, skb, tcp, opts);
                consume_skb(skb);
                regs->verdict.code = NF_STOLEN;
        } else if (tcp->ack) {
                /* ACK from client */
                if (synproxy_recv_client_ack_ipv6(net, skb, tcp, opts,
                                                  ntohl(tcp->seq))) {
                        consume_skb(skb);
                        regs->verdict.code = NF_STOLEN;
                } else {
                        regs->verdict.code = NF_DROP;
                }
        }
}
#endif /* CONFIG_NF_TABLES_IPV6*/

static void nft_synproxy_do_eval(const struct nft_synproxy *priv,
                                 struct nft_regs *regs,
                                 const struct nft_pktinfo *pkt)
{
        struct synproxy_options opts = {};
        struct sk_buff *skb = pkt->skb;
        int thoff = nft_thoff(pkt);
        const struct tcphdr *tcp;
        struct tcphdr _tcph;

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

        if (nf_ip_checksum(skb, nft_hook(pkt), thoff, IPPROTO_TCP)) {
                regs->verdict.code = NF_DROP;
                return;
        }

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

        if (!synproxy_parse_options(skb, thoff, tcp, &opts)) {
                regs->verdict.code = NF_DROP;
                return;
        }

        switch (skb->protocol) {
        case htons(ETH_P_IP):
                nft_synproxy_eval_v4(priv, regs, pkt, tcp, &_tcph, &opts);
                return;
#if IS_ENABLED(CONFIG_NF_TABLES_IPV6)
        case htons(ETH_P_IPV6):
                nft_synproxy_eval_v6(priv, regs, pkt, tcp, &_tcph, &opts);
                return;
#endif
        }
        regs->verdict.code = NFT_BREAK;
}

static int nft_synproxy_do_init(const struct nft_ctx *ctx,
                                const struct nlattr * const tb[],
                                struct nft_synproxy *priv)
{
        struct synproxy_net *snet = synproxy_pernet(ctx->net);
        u32 flags;
        int err;

        if (tb[NFTA_SYNPROXY_MSS])
                priv->info.mss = ntohs(nla_get_be16(tb[NFTA_SYNPROXY_MSS]));
        if (tb[NFTA_SYNPROXY_WSCALE])
                priv->info.wscale = nla_get_u8(tb[NFTA_SYNPROXY_WSCALE]);
        if (tb[NFTA_SYNPROXY_FLAGS]) {
                flags = ntohl(nla_get_be32(tb[NFTA_SYNPROXY_FLAGS]));
                if (flags & ~NF_SYNPROXY_OPT_MASK)
                        return -EOPNOTSUPP;
                priv->info.options = flags;
        }

        err = nf_ct_netns_get(ctx->net, ctx->family);
        if (err)
                return err;

        switch (ctx->family) {
        case NFPROTO_IPV4:
                err = nf_synproxy_ipv4_init(snet, ctx->net);
                if (err)
                        goto nf_ct_failure;
                break;
#if IS_ENABLED(CONFIG_NF_TABLES_IPV6)
        case NFPROTO_IPV6:
                err = nf_synproxy_ipv6_init(snet, ctx->net);
                if (err)
                        goto nf_ct_failure;
                break;
#endif
        case NFPROTO_INET:
                err = nf_synproxy_ipv4_init(snet, ctx->net);
                if (err)
                        goto nf_ct_failure;
                err = nf_synproxy_ipv6_init(snet, ctx->net);
                if (err) {
                        nf_synproxy_ipv4_fini(snet, ctx->net);
                        goto nf_ct_failure;
                }
                break;
        }

        return 0;

nf_ct_failure:
        nf_ct_netns_put(ctx->net, ctx->family);
        return err;
}

static void nft_synproxy_do_destroy(const struct nft_ctx *ctx)
{
        struct synproxy_net *snet = synproxy_pernet(ctx->net);

        switch (ctx->family) {
        case NFPROTO_IPV4:
                nf_synproxy_ipv4_fini(snet, ctx->net);
                break;
#if IS_ENABLED(CONFIG_NF_TABLES_IPV6)
        case NFPROTO_IPV6:
                nf_synproxy_ipv6_fini(snet, ctx->net);
                break;
#endif
        case NFPROTO_INET:
                nf_synproxy_ipv4_fini(snet, ctx->net);
                nf_synproxy_ipv6_fini(snet, ctx->net);
                break;
        }
        nf_ct_netns_put(ctx->net, ctx->family);
}

static int nft_synproxy_do_dump(struct sk_buff *skb, struct nft_synproxy *priv)
{
        if (nla_put_be16(skb, NFTA_SYNPROXY_MSS, htons(priv->info.mss)) ||
            nla_put_u8(skb, NFTA_SYNPROXY_WSCALE, priv->info.wscale) ||
            nla_put_be32(skb, NFTA_SYNPROXY_FLAGS, htonl(priv->info.options)))
                goto nla_put_failure;

        return 0;

nla_put_failure:
        return -1;
}

static void nft_synproxy_eval(const struct nft_expr *expr,
                              struct nft_regs *regs,
                              const struct nft_pktinfo *pkt)
{
        const struct nft_synproxy *priv = nft_expr_priv(expr);

        nft_synproxy_do_eval(priv, regs, pkt);
}

static int nft_synproxy_validate(const struct nft_ctx *ctx,
                                 const struct nft_expr *expr)
{
        if (ctx->family != NFPROTO_IPV4 &&
            ctx->family != NFPROTO_IPV6 &&
            ctx->family != NFPROTO_INET)
                return -EOPNOTSUPP;

        return nft_chain_validate_hooks(ctx->chain, (1 << NF_INET_LOCAL_IN) |
                                                    (1 << NF_INET_FORWARD));
}

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

        return nft_synproxy_do_init(ctx, tb, priv);
}

static void nft_synproxy_destroy(const struct nft_ctx *ctx,
                                 const struct nft_expr *expr)
{
        nft_synproxy_do_destroy(ctx);
}

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

        return nft_synproxy_do_dump(skb, priv);
}

static struct nft_expr_type nft_synproxy_type;
static const struct nft_expr_ops nft_synproxy_ops = {
        .eval           = nft_synproxy_eval,
        .size           = NFT_EXPR_SIZE(sizeof(struct nft_synproxy)),
        .init           = nft_synproxy_init,
        .destroy        = nft_synproxy_destroy,
        .dump           = nft_synproxy_dump,
        .type           = &nft_synproxy_type,
        .validate       = nft_synproxy_validate,
        .reduce         = NFT_REDUCE_READONLY,
};

static struct nft_expr_type nft_synproxy_type __read_mostly = {
        .ops            = &nft_synproxy_ops,
        .name           = "synproxy",
        .owner          = THIS_MODULE,
        .policy         = nft_synproxy_policy,
        .maxattr        = NFTA_SYNPROXY_MAX,
};

static int nft_synproxy_obj_init(const struct nft_ctx *ctx,
                                 const struct nlattr * const tb[],
                                 struct nft_object *obj)
{
        struct nft_synproxy *priv = nft_obj_data(obj);

        return nft_synproxy_do_init(ctx, tb, priv);
}

static void nft_synproxy_obj_destroy(const struct nft_ctx *ctx,
                                     struct nft_object *obj)
{
        nft_synproxy_do_destroy(ctx);
}

static int nft_synproxy_obj_dump(struct sk_buff *skb,
                                 struct nft_object *obj, bool reset)
{
        struct nft_synproxy *priv = nft_obj_data(obj);

        return nft_synproxy_do_dump(skb, priv);
}

static void nft_synproxy_obj_eval(struct nft_object *obj,
                                  struct nft_regs *regs,
                                  const struct nft_pktinfo *pkt)
{
        const struct nft_synproxy *priv = nft_obj_data(obj);

        nft_synproxy_do_eval(priv, regs, pkt);
}

static void nft_synproxy_obj_update(struct nft_object *obj,
                                    struct nft_object *newobj)
{
        struct nft_synproxy *newpriv = nft_obj_data(newobj);
        struct nft_synproxy *priv = nft_obj_data(obj);

        WRITE_ONCE(priv->info, newpriv->info);
}

static struct nft_object_type nft_synproxy_obj_type;
static const struct nft_object_ops nft_synproxy_obj_ops = {
        .type           = &nft_synproxy_obj_type,
        .size           = sizeof(struct nft_synproxy),
        .init           = nft_synproxy_obj_init,
        .destroy        = nft_synproxy_obj_destroy,
        .dump           = nft_synproxy_obj_dump,
        .eval           = nft_synproxy_obj_eval,
        .update         = nft_synproxy_obj_update,
};

static struct nft_object_type nft_synproxy_obj_type __read_mostly = {
        .type           = NFT_OBJECT_SYNPROXY,
        .ops            = &nft_synproxy_obj_ops,
        .maxattr        = NFTA_SYNPROXY_MAX,
        .policy         = nft_synproxy_policy,
        .owner          = THIS_MODULE,
};

static int __init nft_synproxy_module_init(void)
{
        int err;

        err = nft_register_obj(&nft_synproxy_obj_type);
        if (err < 0)
                return err;

        err = nft_register_expr(&nft_synproxy_type);
        if (err < 0)
                goto err;

        return 0;

err:
        nft_unregister_obj(&nft_synproxy_obj_type);
        return err;
}

static void __exit nft_synproxy_module_exit(void)
{
        nft_unregister_expr(&nft_synproxy_type);
        nft_unregister_obj(&nft_synproxy_obj_type);
}

module_init(nft_synproxy_module_init);
module_exit(nft_synproxy_module_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Fernando Fernandez <ffmancera@riseup.net>");
MODULE_ALIAS_NFT_EXPR("synproxy");
MODULE_ALIAS_NFT_OBJ(NFT_OBJECT_SYNPROXY);
MODULE_DESCRIPTION("nftables SYNPROXY expression support");