// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (C) 2007-2008 BalaBit IT Ltd.
 * Author: Krisztian Kovacs
 */
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/module.h>
#include <linux/skbuff.h>
#include <net/tcp.h>
#include <net/udp.h>
#include <net/icmp.h>
#include <net/sock.h>
#include <net/inet_sock.h>
#include <net/netfilter/nf_socket.h>
#if IS_ENABLED(CONFIG_NF_CONNTRACK)
#include <net/netfilter/nf_conntrack.h>
#endif

static int
extract_icmp4_fields(const struct sk_buff *skb, u8 *protocol,
                     __be32 *raddr, __be32 *laddr,
                     __be16 *rport, __be16 *lport)
{
        unsigned int outside_hdrlen = ip_hdrlen(skb);
        struct iphdr *inside_iph, _inside_iph;
        struct icmphdr *icmph, _icmph;
        __be16 *ports, _ports[2];

        icmph = skb_header_pointer(skb, outside_hdrlen,
                                   sizeof(_icmph), &_icmph);
        if (icmph == NULL)
                return 1;

        if (!icmp_is_err(icmph->type))
                return 1;

        inside_iph = skb_header_pointer(skb, outside_hdrlen +
                                        sizeof(struct icmphdr),
                                        sizeof(_inside_iph), &_inside_iph);
        if (inside_iph == NULL)
                return 1;

        if (inside_iph->protocol != IPPROTO_TCP &&
            inside_iph->protocol != IPPROTO_UDP)
                return 1;

        ports = skb_header_pointer(skb, outside_hdrlen +
                                   sizeof(struct icmphdr) +
                                   (inside_iph->ihl << 2),
                                   sizeof(_ports), &_ports);
        if (ports == NULL)
                return 1;

        /* the inside IP packet is the one quoted from our side, thus
         * its saddr is the local address */
        *protocol = inside_iph->protocol;
        *laddr = inside_iph->saddr;
        *lport = ports[0];
        *raddr = inside_iph->daddr;
        *rport = ports[1];

        return 0;
}

static struct sock *
nf_socket_get_sock_v4(struct net *net, struct sk_buff *skb, const int doff,
                      const u8 protocol,
                      const __be32 saddr, const __be32 daddr,
                      const __be16 sport, const __be16 dport,
                      const struct net_device *in)
{
        switch (protocol) {
        case IPPROTO_TCP:
                return inet_lookup(net, skb, doff, saddr, sport, daddr, dport,
                                   in->ifindex);
        case IPPROTO_UDP:
                return udp4_lib_lookup(net, saddr, sport, daddr, dport,
                                       in->ifindex);
        }
        return NULL;
}

struct sock *nf_sk_lookup_slow_v4(struct net *net, const struct sk_buff *skb,
                                  const struct net_device *indev)
{
        __be32 daddr, saddr;
        __be16 dport, sport;
        const struct iphdr *iph = ip_hdr(skb);
        struct sk_buff *data_skb = NULL;
        u8 protocol;
#if IS_ENABLED(CONFIG_NF_CONNTRACK)
        enum ip_conntrack_info ctinfo;
        struct nf_conn const *ct;
#endif
        int doff = 0;

        if (iph->protocol == IPPROTO_UDP || iph->protocol == IPPROTO_TCP) {
                struct tcphdr _hdr;
                struct udphdr *hp;

                hp = skb_header_pointer(skb, ip_hdrlen(skb),
                                        iph->protocol == IPPROTO_UDP ?
                                        sizeof(*hp) : sizeof(_hdr), &_hdr);
                if (hp == NULL)
                        return NULL;

                protocol = iph->protocol;
                saddr = iph->saddr;
                sport = hp->source;
                daddr = iph->daddr;
                dport = hp->dest;
                data_skb = (struct sk_buff *)skb;
                doff = iph->protocol == IPPROTO_TCP ?
                        ip_hdrlen(skb) + __tcp_hdrlen((struct tcphdr *)hp) :
                        ip_hdrlen(skb) + sizeof(*hp);

        } else if (iph->protocol == IPPROTO_ICMP) {
                if (extract_icmp4_fields(skb, &protocol, &saddr, &daddr,
                                         &sport, &dport))
                        return NULL;
        } else {
                return NULL;
        }

#if IS_ENABLED(CONFIG_NF_CONNTRACK)
        /* Do the lookup with the original socket address in
         * case this is a reply packet of an established
         * SNAT-ted connection.
         */
        ct = nf_ct_get(skb, &ctinfo);
        if (ct &&
            ((iph->protocol != IPPROTO_ICMP &&
              ctinfo == IP_CT_ESTABLISHED_REPLY) ||
             (iph->protocol == IPPROTO_ICMP &&
              ctinfo == IP_CT_RELATED_REPLY)) &&
            (ct->status & IPS_SRC_NAT_DONE)) {

                daddr = ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.u3.ip;
                dport = (iph->protocol == IPPROTO_TCP) ?
                        ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.u.tcp.port :
                        ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.u.udp.port;
        }
#endif

        return nf_socket_get_sock_v4(net, data_skb, doff, protocol, saddr,
                                     daddr, sport, dport, indev);
}
EXPORT_SYMBOL_GPL(nf_sk_lookup_slow_v4);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Krisztian Kovacs, Balazs Scheidler");
MODULE_DESCRIPTION("Netfilter IPv4 socket lookup infrastructure");