// See the file "COPYING" in the main distribution directory for copyright.

#include "zeek/packet_analysis/protocol/tcp/TCP.h"

#include "zeek/RunState.h"
#include "zeek/analyzer/protocol/pia/PIA.h"
#include "zeek/packet_analysis/protocol/ip/SessionAdapter.h"
#include "zeek/packet_analysis/protocol/tcp/TCPSessionAdapter.h"

using namespace zeek;
using namespace zeek::packet_analysis::TCP;
using namespace zeek::packet_analysis::IP;

TCPAnalyzer::TCPAnalyzer() : IPBasedAnalyzer("TCP", TRANSPORT_TCP, TCP_PORT_MASK, false) {}

void TCPAnalyzer::Initialize() {}

SessionAdapter* TCPAnalyzer::MakeSessionAdapter(Connection* conn) {
    auto* root = new TCPSessionAdapter(conn);
    root->SetParent(this);

    conn->EnableStatusUpdateTimer();
    conn->SetInactivityTimeout(zeek::detail::udp_inactivity_timeout);

    return root;
}

zeek::analyzer::pia::PIA* TCPAnalyzer::MakePIA(Connection* conn) { return new analyzer::pia::PIA_TCP(conn); }

bool TCPAnalyzer::InitConnKey(size_t len, const uint8_t* data, Packet* packet, IPBasedConnKey& key) {
    uint32_t min_hdr_len = sizeof(struct tcphdr);
    if ( ! CheckHeaderTrunc(min_hdr_len, len, packet) )
        return false;

    const struct tcphdr* tp = reinterpret_cast<const tcphdr*>(packet->ip_hdr->Payload());
    key.InitTuple(packet->ip_hdr->SrcAddr(), tp->th_sport, packet->ip_hdr->DstAddr(), tp->th_dport, packet->proto);

    return true;
}

bool TCPAnalyzer::WantConnection(uint16_t src_port, uint16_t dst_port, const u_char* data, bool& flip_roles) const {
    flip_roles = false;
    const struct tcphdr* tp = reinterpret_cast<const tcphdr*>(data);
    uint8_t tcp_flags = tp->th_flags;

    if ( ! (tcp_flags & TH_SYN) || (tcp_flags & TH_ACK) ) {
        // The new connection is starting either without a SYN,
        // or with a SYN ack. This means it's a partial connection.
        if ( ! zeek::detail::partial_connection_ok )
            return false;

        if ( tcp_flags & TH_SYN && ! zeek::detail::tcp_SYN_ack_ok )
            return false;

        // Try to guess true responder by the port numbers.
        // (We might also think that for SYN acks we could
        // safely flip the roles, but that doesn't work
        // for stealth scans.)
        if ( IsLikelyServerPort(src_port) ) { // connection is a candidate for flipping
            if ( IsLikelyServerPort(dst_port) )
                // Hmmm, both source and destination
                // are plausible.  Heuristic: flip only
                // if (1) this isn't a SYN ACK (to avoid
                // confusing stealth scans) and
                // (2) dest port > src port (to favor
                // more plausible servers).
                flip_roles = ! (tcp_flags & TH_SYN) && src_port < dst_port;
            else
                // Source is plausible, destination isn't.
                flip_roles = true;
        }
    }

    return true;
}

void TCPAnalyzer::DeliverPacket(Connection* c, double t, bool is_orig, int remaining, Packet* pkt) {
    const u_char* data = pkt->ip_hdr->Payload();
    int len = pkt->ip_hdr->PayloadLen();
    // If the header length is zero, tcp checksum offloading is probably enabled
    // In this case, let's fix up the length.
    if ( pkt->ip_hdr->TotalLen() == 0 )
        len = remaining;
    auto* adapter = static_cast<TCPSessionAdapter*>(c->GetSessionAdapter());

    const struct tcphdr* tp = ExtractTCP_Header(data, len, remaining, adapter);
    if ( ! tp ) {
        adapter->TapPacket(pkt, PacketAction::Skip, SkipReason::BadProtoHeader);
        return;
    }

    // We need the min() here because Ethernet frame padding can lead to
    // remaining > len.
    if ( packet_contents )
        adapter->PacketContents(data, std::min(len, remaining));

    analyzer::tcp::TCP_Endpoint* endpoint = is_orig ? adapter->orig : adapter->resp;
    analyzer::tcp::TCP_Endpoint* peer = endpoint->peer;
    const std::shared_ptr<IP_Hdr>& ip = pkt->ip_hdr;

    if ( ! ValidateChecksum(ip.get(), tp, endpoint, len, remaining, adapter) ) {
        adapter->TapPacket(pkt, PacketAction::Skip, SkipReason::BadChecksum);
        return;
    }

    // Store the session in the packet in case we get an encapsulation here. We need it for
    // handling those properly.
    pkt->session = c;

    // Tap the packet before processing/forwarding.
    adapter->TapPacket(pkt);

    // Adapter Process() updates the state of TCP connections.
    //
    // Watch out: The connection can flip from under us on the second packet
    // (see TCP_Endpoint::CheckHistory()) and this causes the local is_orig
    // parameter to be stale. I.e., child analyzers that receive packet
    // and stream data further down via adapter->DeliverPacket(...) will
    // have been flipped, so we need to ensure they receive the correct
    // is_orig value. We flip the local is_orig by checking if the originator
    // endpoint has changed after adapter->Process() ran.
    //
    // See the docs/devel/conn.rst for more details and ideas how to
    // improve here. This pretty tricky and fragile.
    const auto* originator = adapter->Orig();

    adapter->Process(is_orig, tp, len, ip, data, remaining);

    // If the connection flipped during adapter->Process(), update the local is_orig
    // to reflect that so that child analyzers observe the right value.
    if ( originator != adapter->Orig() )
        is_orig = ! is_orig;

    // Send the packet back into the packet analysis framework.
    ForwardPacket(std::min(len, remaining), data, pkt);

    // Call DeliverPacket on the adapter directly here. Normally we'd call ForwardPacket
    // but this adapter does some other things in its DeliverPacket with the packet children
    // analyzers.
    adapter->DeliverPacket(std::min(len, remaining), data, is_orig, adapter->LastRelDataSeq(), ip.get(), pkt->cap_len);
}

const struct tcphdr* TCPAnalyzer::ExtractTCP_Header(const u_char*& data, int& len, int& remaining,
                                                    TCPSessionAdapter* adapter) {
    const struct tcphdr* tp = reinterpret_cast<const tcphdr*>(data);
    uint32_t tcp_hdr_len = tp->th_off * 4;

    if ( tcp_hdr_len < sizeof(struct tcphdr) ) {
        adapter->Weird("bad_TCP_header_len");
        return nullptr;
    }

    if ( tcp_hdr_len > static_cast<uint32_t>(len) || tcp_hdr_len > static_cast<uint32_t>(remaining) ) {
        // This can happen even with the above test, due to TCP options.
        adapter->Weird("truncated_header");
        return nullptr;
    }

    len -= tcp_hdr_len; // remove TCP header
    remaining -= tcp_hdr_len;
    data += tcp_hdr_len;

    return tp;
}

bool TCPAnalyzer::ValidateChecksum(const IP_Hdr* ip, const struct tcphdr* tp, analyzer::tcp::TCP_Endpoint* endpoint,
                                   int len, int caplen, TCPSessionAdapter* adapter) {
    if ( ! run_state::current_pkt->l4_checksummed && ! zeek::detail::ignore_checksums &&
         ! GetIgnoreChecksumsNets()->Contains(ip->IPHeaderSrcAddr()) && caplen >= len &&
         ! endpoint->ValidChecksum(tp, len, ip->IP4_Hdr()) ) {
        adapter->Weird("bad_TCP_checksum");
        endpoint->ChecksumError();
        return false;
    }
    else
        return true;
}
