// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (C) 2007-2008 BalaBit IT Ltd.
 * Author: Krisztian Kovacs
 */

#include <net/netfilter/nf_tproxy.h>
#include <linux/module.h>
#include <linux/skbuff.h>
#include <net/sock.h>
#include <net/inet_sock.h>
#include <linux/ip.h>
#include <net/checksum.h>
#include <net/udp.h>
#include <net/tcp.h>
#include <linux/inetdevice.h>

struct sock *
nf_tproxy_handle_time_wait4(struct net *net, struct sk_buff *skb,
                         __be32 laddr, __be16 lport, struct sock *sk)
{
        const struct iphdr *iph = ip_hdr(skb);
        struct tcphdr _hdr, *hp;

        hp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(_hdr), &_hdr);
        if (hp == NULL) {
                inet_twsk_put(inet_twsk(sk));
                return NULL;
        }

        if (hp->syn && !hp->rst && !hp->ack && !hp->fin) {
                /* SYN to a TIME_WAIT socket, we'd rather redirect it
                 * to a listener socket if there's one */
                struct sock *sk2;

                sk2 = nf_tproxy_get_sock_v4(net, skb, iph->protocol,
                                            iph->saddr, laddr ? laddr : iph->daddr,
                                            hp->source, lport ? lport : hp->dest,
                                            skb->dev, NF_TPROXY_LOOKUP_LISTENER);
                if (sk2) {
                        nf_tproxy_twsk_deschedule_put(inet_twsk(sk));
                        sk = sk2;
                }
        }

        return sk;
}
EXPORT_SYMBOL_GPL(nf_tproxy_handle_time_wait4);

__be32 nf_tproxy_laddr4(struct sk_buff *skb, __be32 user_laddr, __be32 daddr)
{
        const struct in_ifaddr *ifa;
        struct in_device *indev;
        __be32 laddr;

        if (user_laddr)
                return user_laddr;

        laddr = 0;
        indev = __in_dev_get_rcu(skb->dev);
        if (!indev)
                return daddr;

        in_dev_for_each_ifa_rcu(ifa, indev) {
                if (ifa->ifa_flags & IFA_F_SECONDARY)
                        continue;

                laddr = ifa->ifa_local;
                break;
        }

        return laddr ? laddr : daddr;
}
EXPORT_SYMBOL_GPL(nf_tproxy_laddr4);

struct sock *
nf_tproxy_get_sock_v4(struct net *net, struct sk_buff *skb,
                      const u8 protocol,
                      const __be32 saddr, const __be32 daddr,
                      const __be16 sport, const __be16 dport,
                      const struct net_device *in,
                      const enum nf_tproxy_lookup_t lookup_type)
{
        struct sock *sk;

        switch (protocol) {
        case IPPROTO_TCP: {
                struct tcphdr _hdr, *hp;

                hp = skb_header_pointer(skb, ip_hdrlen(skb),
                                        sizeof(struct tcphdr), &_hdr);
                if (hp == NULL)
                        return NULL;

                switch (lookup_type) {
                case NF_TPROXY_LOOKUP_LISTENER:
                        sk = inet_lookup_listener(net, skb,
                                                  ip_hdrlen(skb) + __tcp_hdrlen(hp),
                                                  saddr, sport, daddr, dport,
                                                  in->ifindex, 0);

                        if (sk && !refcount_inc_not_zero(&sk->sk_refcnt))
                                sk = NULL;
                        /* NOTE: we return listeners even if bound to
                         * 0.0.0.0, those are filtered out in
                         * xt_socket, since xt_TPROXY needs 0 bound
                         * listeners too
                         */
                        break;
                case NF_TPROXY_LOOKUP_ESTABLISHED:
                        sk = inet_lookup_established(net, saddr, sport,
                                                     daddr, dport, in->ifindex);
                        break;
                default:
                        BUG();
                }
                break;
                }
        case IPPROTO_UDP:
                sk = udp4_lib_lookup(net, saddr, sport, daddr, dport,
                                     in->ifindex);
                if (sk) {
                        int connected = (sk->sk_state == TCP_ESTABLISHED);
                        int wildcard = (inet_sk(sk)->inet_rcv_saddr == 0);

                        /* NOTE: we return listeners even if bound to
                         * 0.0.0.0, those are filtered out in
                         * xt_socket, since xt_TPROXY needs 0 bound
                         * listeners too
                         */
                        if ((lookup_type == NF_TPROXY_LOOKUP_ESTABLISHED &&
                              (!connected || wildcard)) ||
                            (lookup_type == NF_TPROXY_LOOKUP_LISTENER && connected)) {
                                sock_put(sk);
                                sk = NULL;
                        }
                }
                break;
        default:
                WARN_ON(1);
                sk = NULL;
        }

        pr_debug("tproxy socket lookup: proto %u %08x:%u -> %08x:%u, lookup type: %d, sock %p\n",
                 protocol, ntohl(saddr), ntohs(sport), ntohl(daddr), ntohs(dport), lookup_type, sk);

        return sk;
}
EXPORT_SYMBOL_GPL(nf_tproxy_get_sock_v4);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Balazs Scheidler, Krisztian Kovacs");
MODULE_DESCRIPTION("Netfilter IPv4 transparent proxy support");