/**
* nfq_ip_mangle - mangle IPv4 packet buffer
* \param pktb: pointer to network packet buffer
* \param dataoff: offset to layer 4 header
* \param match_offset: offset to content that you want to mangle
* \param match_len: length of the existing content you want to mangle
* \param rep_buffer: pointer to data you want to use to replace current content
* \param rep_len: length of data you want to use to replace current content
*
* \note This function recalculates the IPv4 checksum (if needed).
*/
int nfq_ip_mangle(struct pkt_buff *pkt, unsigned int dataoff,
unsigned int match_offset, unsigned int match_len,
const char *rep_buffer, unsigned int rep_len)
{
struct iphdr *iph = (struct iphdr *) pkt->network_header;
if (!pktb_mangle(pkt, dataoff, match_offset, match_len,
rep_buffer, rep_len))
return 0;
/* fix IP hdr checksum information */
iph->tot_len = htons(pkt->len);
nfq_ip_set_checksum(iph);
return 1;
}
static int cb(
struct nfq_q_handle *q,
struct nfgenmsg *nfmsg,
struct nfq_data *nfa,
void *arg
) {
int id = 0;
struct nfqnl_msg_packet_hdr *ph;
size_t packet_length;
unsigned char *packet_data;
struct pkt_buff *packet;
struct iphdr *ip_header;
struct tcphdr *tcp_header;
ph = nfq_get_msg_packet_hdr(nfa);
if (ph) {
id = ntohl(ph->packet_id);
}
packet_length = nfq_get_payload(nfa, &packet_data);
packet = pktb_alloc(AF_INET, packet_data, packet_length, 4096);
ip_header = nfq_ip_get_hdr(packet);
nfq_ip_set_transport_header(packet, ip_header);
tcp_header = nfq_tcp_get_hdr(packet);
if (ip_header) {
struct in_addr *target;
if (src_or_dst == src) {
target = (struct in_addr *) &ip_header->saddr;
} else if (src_or_dst == dst) {
target = (struct in_addr *) &ip_header->daddr;
}
inet_aton(target_ip_address, target);
nfq_ip_set_checksum(ip_header);
nfq_tcp_compute_checksum_ipv4(tcp_header, ip_header);
memcpy(packet_data, pktb_data(packet), packet_length);
}
pktb_free(packet);
return nfq_set_verdict(q, id, NF_ACCEPT, packet_length, packet_data);
}
