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

#include "zeek/packet_analysis/protocol/iptunnel/IPTunnel.h"

#include <pcap.h> // For DLT_ constants

#include "zeek/Conn.h"
#include "zeek/IP.h"
#include "zeek/RunState.h"
#include "zeek/TunnelEncapsulation.h"
#include "zeek/packet_analysis/protocol/ip/IP.h"

namespace zeek::packet_analysis::IPTunnel {

IPTunnelAnalyzer* ip_tunnel_analyzer;

IPTunnelAnalyzer::IPTunnelAnalyzer() : zeek::packet_analysis::Analyzer("IPTunnel") { ip_tunnel_analyzer = this; }

bool IPTunnelAnalyzer::AnalyzePacket(size_t len, const uint8_t* data, Packet* packet) {
    if ( ! packet->ip_hdr ) {
        reporter->InternalError("IPTunnelAnalyzer: null ip_hdr in packet");
        return false;
    }

    if ( packet->encap && packet->encap->Depth() >= BifConst::Tunnel::max_depth ) {
        Weird("exceeded_tunnel_max_depth", packet);
        return false;
    }

    int proto = packet->proto;
    int gre_version = packet->gre_version;
    BifEnum::Tunnel::Type tunnel_type = packet->tunnel_type;
    int gre_link_type = packet->gre_link_type;

    std::shared_ptr<IP_Hdr> inner = nullptr;

    if ( gre_version != 0 ) {
        // Check for a valid inner packet first.
        auto result = packet_analysis::IP::ParsePacket(len, data, proto, inner);
        if ( result == packet_analysis::IP::ParseResult::BadProtocol )
            Weird("invalid_inner_IP_version", packet);
        else if ( result < packet_analysis::IP::ParseResult::CaplenTooSmall )
            Weird("truncated_inner_IP", packet);
        else if ( result > packet_analysis::IP::ParseResult::CaplenTooLarge )
            Weird("inner_IP_payload_length_mismatch", packet);

        if ( result != packet_analysis::IP::ParseResult::Ok )
            return false;
    }

    // Look up to see if we've already seen this IP tunnel, identified
    // by the pair of IP addresses, so that we can always associate the
    // same UID with it.
    IPPair tunnel_idx;
    if ( packet->ip_hdr->SrcAddr() < packet->ip_hdr->DstAddr() )
        tunnel_idx = IPPair(packet->ip_hdr->SrcAddr(), packet->ip_hdr->DstAddr());
    else
        tunnel_idx = IPPair(packet->ip_hdr->DstAddr(), packet->ip_hdr->SrcAddr());

    IPTunnelMap::iterator tunnel_it = ip_tunnels.find(tunnel_idx);

    if ( tunnel_it == ip_tunnels.end() ) {
        EncapsulatingConn ec(packet->ip_hdr->SrcAddr(), packet->ip_hdr->DstAddr(), tunnel_type);
        ip_tunnels[tunnel_idx] = TunnelActivity(ec, run_state::network_time);
        zeek::detail::timer_mgr->Add(new detail::IPTunnelTimer(run_state::network_time, tunnel_idx, this));
    }
    else
        tunnel_it->second.second = zeek::run_state::network_time;

    if ( gre_version == 0 )
        return ProcessEncapsulatedPacket(run_state::processing_start_time, packet, len, len, data, gre_link_type,
                                         packet->encap, ip_tunnels[tunnel_idx].first);
    else
        return ProcessEncapsulatedPacket(run_state::processing_start_time, packet, inner, packet->encap,
                                         ip_tunnels[tunnel_idx].first);
}

/**
 * Handles a packet that contains an IP header directly after the tunnel header.
 */
bool IPTunnelAnalyzer::ProcessEncapsulatedPacket(double t, const Packet* pkt, const std::shared_ptr<IP_Hdr>& inner,
                                                 std::shared_ptr<EncapsulationStack> prev,
                                                 const EncapsulatingConn& ec) {
    uint32_t caplen, len;
    caplen = len = inner->TotalLen();

    pkt_timeval ts;
    int link_type;

    if ( pkt )
        ts = pkt->ts;
    else {
        ts.tv_sec = (time_t)run_state::network_time;
        ts.tv_usec = (suseconds_t)((run_state::network_time - (double)ts.tv_sec) * 1000000);
    }

    const u_char* data = nullptr;

    if ( inner->IP4_Hdr() )
        data = (const u_char*)inner->IP4_Hdr();
    else
        data = (const u_char*)inner->IP6_Hdr();

    auto outer = prev ? prev : std::make_shared<EncapsulationStack>();
    outer->Add(ec);

    // Construct fake packet containing the inner packet so it can be processed
    // like a normal one.
    Packet p;
    p.Init(DLT_RAW, &ts, caplen, len, data, false, "");
    p.encap = outer;

    // Forward the packet back to the IP analyzer.
    bool return_val = ForwardPacket(len, data, &p);

    return return_val;
}

/**
 * Handles a packet that contains a physical-layer header after the tunnel header.
 */
bool IPTunnelAnalyzer::ProcessEncapsulatedPacket(double t, const Packet* pkt, uint32_t caplen, uint32_t len,
                                                 const u_char* data, int link_type,
                                                 std::shared_ptr<EncapsulationStack> prev,
                                                 const EncapsulatingConn& ec) {
    pkt_timeval ts;

    if ( pkt )
        ts = pkt->ts;
    else {
        ts.tv_sec = (time_t)run_state::network_time;
        ts.tv_usec = (suseconds_t)((run_state::network_time - (double)ts.tv_sec) * 1000000);
    }

    auto outer = prev ? prev : std::make_shared<EncapsulationStack>();
    outer->Add(ec);

    // Construct fake packet containing the inner packet so it can be processed
    // like a normal one.
    Packet p;
    p.Init(link_type, &ts, caplen, len, data, false, "");
    p.encap = outer;

    // Process the packet as if it was a brand new packet by passing it back
    // to the packet manager.
    bool return_val = packet_mgr->ProcessInnerPacket(&p);

    return return_val;
}

std::unique_ptr<Packet> build_inner_packet(Packet* outer_pkt, int* encap_index,
                                           std::shared_ptr<EncapsulationStack> encap_stack, uint32_t inner_cap_len,
                                           const u_char* data, int link_type, BifEnum::Tunnel::Type tunnel_type,
                                           const Tag& analyzer_tag) {
    assert(outer_pkt->cap_len >= inner_cap_len);
    assert(outer_pkt->len >= outer_pkt->cap_len - inner_cap_len);

    // Compute the wire length of the inner packet based on the wire length of
    // the outer and the difference in capture lengths. This ensures that for
    // truncated packets the wire length of the inner packet stays intact. Wire
    // length may be greater than data available for truncated packets. However,
    // analyzers do validate lengths found in headers with the wire length
    // of the packet and keeping it consistent avoids violations.
    uint32_t consumed_len = outer_pkt->cap_len - inner_cap_len;
    uint32_t inner_wire_len = outer_pkt->len - consumed_len;

    auto inner_pkt = std::make_unique<Packet>(link_type, &outer_pkt->ts, inner_cap_len, inner_wire_len, data);

    *encap_index = 0;
    if ( outer_pkt->session ) {
        EncapsulatingConn inner(static_cast<Connection*>(outer_pkt->session), tunnel_type);

        if ( ! outer_pkt->encap )
            outer_pkt->encap = encap_stack != nullptr ? encap_stack : std::make_shared<EncapsulationStack>();

        outer_pkt->encap->Add(inner);
        inner_pkt->encap = outer_pkt->encap;
        *encap_index = outer_pkt->encap->Depth();
    }

    return inner_pkt;
}

namespace detail {

IPTunnelTimer::IPTunnelTimer(double t, IPTunnelAnalyzer::IPPair p, IPTunnelAnalyzer* analyzer)
    : Timer(t + BifConst::Tunnel::ip_tunnel_timeout, zeek::detail::TIMER_IP_TUNNEL_INACTIVITY),
      tunnel_idx(std::move(p)),
      analyzer(analyzer) {}

void IPTunnelTimer::Dispatch(double t, bool is_expire) {
    IPTunnelAnalyzer::IPTunnelMap::const_iterator it = analyzer->ip_tunnels.find(tunnel_idx);

    if ( it == analyzer->ip_tunnels.end() )
        return;

    double last_active = it->second.second;
    double inactive_time = t > last_active ? t - last_active : 0;

    if ( inactive_time >= BifConst::Tunnel::ip_tunnel_timeout )
        // tunnel activity timed out, delete it from map
        analyzer->ip_tunnels.erase(tunnel_idx);

    else if ( ! is_expire )
        // tunnel activity didn't timeout, schedule another timer
        zeek::detail::timer_mgr->Add(new IPTunnelTimer(t, tunnel_idx, analyzer));
}

} // namespace detail

} // namespace zeek::packet_analysis::IPTunnel
