ipv4.c

/*
 * (C) 2012 by Pablo Neira Ayuso <pablo@netfilter.org>
 *
 * 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 code has been sponsored by Vyatta Inc. <http://www.vyatta.com>
 */

#include <stdio.h>
#include <stdbool.h>
#include <arpa/inet.h>
#include <netinet/ip.h>

#include <libnetfilter_queue/libnetfilter_queue.h>
#include <libnetfilter_queue/libnetfilter_queue_ipv4.h>
#include <libnetfilter_queue/pktbuff.h>

#include "internal.h"

EXPORT_SYMBOL
struct iphdr *nfq_ip_get_hdr(struct pkt_buff *pktb)
{
        struct iphdr *iph;
        unsigned int pktlen = pktb_tail(pktb) - pktb->network_header;

        /* Not enough room for IPv4 header. */
        if (pktlen < sizeof(struct iphdr))
                return NULL;

        iph = (struct iphdr *)pktb->network_header;

        /* Not IPv4 packet. */
        if (iph->version != 4)
                return NULL;

        /* Malformed IPv4 total length field. */
        if (ntohs(iph->tot_len) > pktlen)
                return NULL;

        return iph;
}

EXPORT_SYMBOL
int nfq_ip_set_transport_header(struct pkt_buff *pktb, struct iphdr *iph)
{
        int doff = iph->ihl * 4;

        /* Wrong offset to IPv4 payload. */
        if ((int)pktb->len - doff <= 0)
                return -1;

        pktb->transport_header = pktb->network_header + doff;
        return 0;
}

EXPORT_SYMBOL
void nfq_ip_set_checksum(struct iphdr *iph)
{
        uint32_t iph_len = iph->ihl * 4;

        iph->check = 0;
        iph->check = nfq_checksum(0, (uint16_t *)iph, iph_len);
}

EXPORT_SYMBOL
int nfq_ip_mangle(struct pkt_buff *pktb, unsigned int dataoff,
                  unsigned int match_offset, unsigned int match_len,
                  const char *rep_buffer, unsigned int rep_len)
{
        struct iphdr *iph = (struct iphdr *) pktb->network_header;

        if (!pktb_mangle(pktb, dataoff, match_offset, match_len, rep_buffer,
                         rep_len))
                return 0;

        /* fix IP hdr checksum information */
        iph->tot_len = htons(pktb_tail(pktb) - pktb->network_header);
        nfq_ip_set_checksum(iph);

        return 1;
}

EXPORT_SYMBOL
int nfq_ip_snprintf(char *buf, size_t size, const struct iphdr *iph)
{
        int ret;
        struct in_addr src = { iph->saddr };
        struct in_addr dst = { iph->daddr };

        char src_str[INET_ADDRSTRLEN];
        char dst_str[INET_ADDRSTRLEN];

        ret = snprintf(buf, size, "SRC=%s DST=%s LEN=%u TOS=0x%X "
                                  "PREC=0x%X TTL=%u ID=%u PROTO=%u ",
                        inet_ntop(AF_INET, &src, src_str, INET_ADDRSTRLEN),
                        inet_ntop(AF_INET, &dst, dst_str, INET_ADDRSTRLEN),
                        ntohs(iph->tot_len), IPTOS_TOS(iph->tos),
                        IPTOS_PREC(iph->tos), iph->ttl, ntohs(iph->id),
                        iph->protocol);

        return ret;
}