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/*
*****************************************************************************
*
* File: process_packet.c
*
* Author: Damien S. Stuart
*
* Purpose: Packet parser/decoder for fwknopd server. Takes the raw packet
* data from libpcap and parses/extracts the packet data payload,
* then creates an FKO context with that data. If the context
* creation is successful, it is queued for processing.
*
* Copyright 2010 Damien Stuart (dstuart@dstuart.org)
*
* License (GNU Public License):
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
* USA
*
*****************************************************************************
*/
#include <pcap.h>

#include "fwknopd_common.h"
#include "netinet_common.h"
#include "process_packet.h"
#include "incoming_spa.h"
#include "utils.h"

void
process_packet(unsigned char *args, const struct pcap_pkthdr *packet_header,
    const unsigned char *packet)
{
    struct ether_header *eth_p;
    struct iphdr *iph_p;
    struct tcphdr *tcph_p;
    struct udphdr *udph_p;

    unsigned char *pkt_data;
    unsigned short pkt_data_len;
    unsigned char *pkt_end;

    unsigned int ip_hdr_words;

    unsigned char proto;
    unsigned int src_ip;
    unsigned int dst_ip;

    unsigned short src_port;
    unsigned short dst_port;

    unsigned short eth_type;

    fko_srv_options_t *opts = (fko_srv_options_t *)args;

    int offset = opts->data_link_offset;

    unsigned short pkt_len = packet_header->len;

    /* This is a hack to determine if we are using the linux cooked
* interface. We base it on the offset being 16 which is the
* value it would be if the datalink is DLT_LINUX_SLL. I don't
* know if this is the correct way to do this, but it seems to work.
*/
    unsigned char assume_cooked = (offset == 16 ? 1 : 0);

    /* Determine packet end.
*/
    pkt_end = (unsigned char *) packet + packet_header->caplen;

    /* The ethernet header.
*/
    eth_p = (struct ether_header*) packet;

    /* Gotta have a complete ethernet header.
*/
    if (packet_header->caplen < ETHER_HDR_LEN)
        return;

    eth_type = ntohs(*((unsigned short*)&eth_p->ether_type));

    if(eth_type == 0x8100) /* 802.1q encapsulated */
    {
        offset += 4;
        eth_type = ntohs(*(((unsigned short*)&eth_p->ether_type)+2));
    }

    /* When using libpcap, pkthdr->len for 802.3 frames include CRC_LEN,
* but Ethenet_II frames do not.
*/
    if (eth_type > 1500 || assume_cooked == 1)
    {
        pkt_len += ETHER_CRC_LEN;

        if(eth_type == 0xAAAA) /* 802.2 SNAP */
            offset += 5;
    }
    else /* 802.3 Frame */
        offset += 3;

    /* Make sure the packet length is still valid.
*/
    if (! ETHER_IS_VALID_LEN(pkt_len) )
        return;

    /* Pull the IP header.
*/
    iph_p = (struct iphdr*)(packet + offset);

    /* If IP header is past calculated packet end, bail.
*/
    if ((unsigned char*)(iph_p + 1) > pkt_end)
        return;

    /* ip_hdr_words is the number of 32 bit words in the IP header. After
* masking of the IPV4 version bits, the number *must* be at least
* 5, even without options.
*/
    ip_hdr_words = iph_p->ihl & IPV4_VER_MASK;

    if (ip_hdr_words < MIN_IPV4_WORDS)
        return;

    /* Now, find the packet data payload (depending on IPPROTO).
*/
    src_ip = iph_p->saddr;
    dst_ip = iph_p->daddr;

    proto = iph_p->protocol;

    if (proto == IPPROTO_TCP)
    {
        /* Process TCP packet
*/
        tcph_p = (struct tcphdr*)((unsigned char*)iph_p + (ip_hdr_words << 2));

        src_port = ntohs(tcph_p->source);
        dst_port = ntohs(tcph_p->dest);

        pkt_data = ((unsigned char*)(tcph_p+1))+((tcph_p->doff)<<2)-sizeof(struct tcphdr);

        pkt_data_len = (pkt_end-(unsigned char*)iph_p)-(pkt_data-(unsigned char*)iph_p);
    }
    else if (proto == IPPROTO_UDP)
    {
        /* Process UDP packet
*/
        udph_p = (struct udphdr*)((unsigned char*)iph_p + (ip_hdr_words << 2));

        src_port = ntohs(udph_p->source);
        dst_port = ntohs(udph_p->dest);

        pkt_data = ((unsigned char*)(udph_p + 1));
        pkt_data_len = (pkt_end-(unsigned char*)iph_p)-(pkt_data-(unsigned char*)iph_p);
    }
    else
        return;

    /*
* Now we have data. For now, we are not checking IP or port values. We
* are relying on the pcap filter. This may change so we do retain the IP
* addresses and ports just in case. We just go ahead and queue the
* data.
*/

    /* Expect the data to be at least the minimum required size. This check
* will weed out a lot of things like small TCP ACK's if the user has a
* permissive pcap filter
*/
    if(pkt_data_len < MIN_SPA_DATA_SIZE)
        return;

    /* Expect the data to not be too large
*/
    if(pkt_data_len > MAX_SPA_PACKET_LEN)
        return;

    /* Copy the packet for SPA processing
*/
    strlcpy((char *)opts->spa_pkt.packet_data, (char *)pkt_data, pkt_data_len+1);
    opts->spa_pkt.packet_data_len = pkt_data_len;
    opts->spa_pkt.packet_proto = proto;
    opts->spa_pkt.packet_src_ip = src_ip;
    opts->spa_pkt.packet_dst_ip = dst_ip;
    opts->spa_pkt.packet_src_port = src_port;
    opts->spa_pkt.packet_dst_port = dst_port;

    incoming_spa(opts);

    return;
}

/***EOF***/
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