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#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <time.h>
#include <arpa/inet.h>
#include <libmnl/libmnl.h>
#include <linux/netfilter.h>
#include <linux/netfilter/nfnetlink.h>
#include <linux/types.h>
#include <linux/netfilter/nfnetlink_queue.h>
#include <libnetfilter_queue/libnetfilter_queue.h>
/* only for NFQA_CT, not needed otherwise: */
#include <linux/netfilter/nfnetlink_conntrack.h>
static struct mnl_socket *nl;
static void
nfq_send_verdict(int queue_num, uint32_t id)
{
char buf[MNL_SOCKET_BUFFER_SIZE];
struct nlmsghdr *nlh;
struct nlattr *nest;
nlh = nfq_nlmsg_put(buf, NFQNL_MSG_VERDICT, queue_num);
nfq_nlmsg_verdict_put(nlh, id, NF_ACCEPT);
/* example to set the connmark. First, start NFQA_CT section: */
nest = mnl_attr_nest_start(nlh, NFQA_CT);
/* then, add the connmark attribute: */
mnl_attr_put_u32(nlh, CTA_MARK, htonl(42));
/* more conntrack attributes, e.g. CTA_LABELS could be set here */
/* end conntrack section */
mnl_attr_nest_end(nlh, nest);
if (mnl_socket_sendto(nl, nlh, nlh->nlmsg_len) < 0) {
perror("mnl_socket_send");
exit(EXIT_FAILURE);
}
}
static int queue_cb(const struct nlmsghdr *nlh, void *data)
{
struct nfqnl_msg_packet_hdr *ph = NULL;
struct nlattr *attr[NFQA_MAX+1] = {};
uint32_t id = 0, skbinfo;
struct nfgenmsg *nfg;
uint16_t plen;
if (nfq_nlmsg_parse(nlh, attr) < 0) {
perror("problems parsing");
return MNL_CB_ERROR;
}
nfg = mnl_nlmsg_get_payload(nlh);
if (attr[NFQA_PACKET_HDR] == NULL) {
fputs("metaheader not set\n", stderr);
return MNL_CB_ERROR;
}
ph = mnl_attr_get_payload(attr[NFQA_PACKET_HDR]);
plen = mnl_attr_get_payload_len(attr[NFQA_PAYLOAD]);
/* void *payload = mnl_attr_get_payload(attr[NFQA_PAYLOAD]); */
skbinfo = attr[NFQA_SKB_INFO] ? ntohl(mnl_attr_get_u32(attr[NFQA_SKB_INFO])) : 0;
if (attr[NFQA_CAP_LEN]) {
uint32_t orig_len = ntohl(mnl_attr_get_u32(attr[NFQA_CAP_LEN]));
if (orig_len != plen)
printf("truncated ");
}
if (skbinfo & NFQA_SKB_GSO)
printf("GSO ");
id = ntohl(ph->packet_id);
printf("packet received (id=%u hw=0x%04x hook=%u, payload len %u",
id, ntohs(ph->hw_protocol), ph->hook, plen);
/*
* ip/tcp checksums are not yet valid, e.g. due to GRO/GSO.
* The application should behave as if the checksums are correct.
*
* If these packets are later forwarded/sent out, the checksums will
* be corrected by kernel/hardware.
*/
if (skbinfo & NFQA_SKB_CSUMNOTREADY)
printf(", checksum not ready");
puts(")");
nfq_send_verdict(ntohs(nfg->res_id), id);
return MNL_CB_OK;
}
int main(int argc, char *argv[])
{
char *buf;
/* largest possible packet payload, plus netlink data overhead: */
size_t sizeof_buf = 0xffff + (MNL_SOCKET_BUFFER_SIZE/2);
struct nlmsghdr *nlh;
int ret;
unsigned int portid, queue_num;
if (argc != 2) {
printf("Usage: %s [queue_num]\n", argv[0]);
exit(EXIT_FAILURE);
}
queue_num = atoi(argv[1]);
nl = mnl_socket_open(NETLINK_NETFILTER);
if (nl == NULL) {
perror("mnl_socket_open");
exit(EXIT_FAILURE);
}
if (mnl_socket_bind(nl, 0, MNL_SOCKET_AUTOPID) < 0) {
perror("mnl_socket_bind");
exit(EXIT_FAILURE);
}
portid = mnl_socket_get_portid(nl);
buf = malloc(sizeof_buf);
if (!buf) {
perror("allocate receive buffer");
exit(EXIT_FAILURE);
}
nlh = nfq_nlmsg_put(buf, NFQNL_MSG_CONFIG, queue_num);
nfq_nlmsg_cfg_put_cmd(nlh, AF_INET, NFQNL_CFG_CMD_BIND);
if (mnl_socket_sendto(nl, nlh, nlh->nlmsg_len) < 0) {
perror("mnl_socket_send");
exit(EXIT_FAILURE);
}
nlh = nfq_nlmsg_put(buf, NFQNL_MSG_CONFIG, queue_num);
nfq_nlmsg_cfg_put_params(nlh, NFQNL_COPY_PACKET, 0xffff);
mnl_attr_put_u32(nlh, NFQA_CFG_FLAGS, htonl(NFQA_CFG_F_GSO));
mnl_attr_put_u32(nlh, NFQA_CFG_MASK, htonl(NFQA_CFG_F_GSO));
if (mnl_socket_sendto(nl, nlh, nlh->nlmsg_len) < 0) {
perror("mnl_socket_send");
exit(EXIT_FAILURE);
}
/* ENOBUFS is signalled to userspace when packets were lost
* on kernel side. In most cases, userspace isn't interested
* in this information, so turn it off.
*/
ret = 1;
mnl_socket_setsockopt(nl, NETLINK_NO_ENOBUFS, &ret, sizeof(int));
for (;;) {
ret = mnl_socket_recvfrom(nl, buf, sizeof_buf);
if (ret == -1) {
perror("mnl_socket_recvfrom");
exit(EXIT_FAILURE);
}
ret = mnl_cb_run(buf, ret, 0, portid, queue_cb, NULL);
if (ret < 0){
perror("mnl_cb_run");
exit(EXIT_FAILURE);
}
}
mnl_socket_close(nl);
return 0;
}
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