Originally Posted by teckk
(Post 6448557)
My 2 cents.
Interesting. I wanted to see that work. You'll need python bindings for that if you use python.
Code:
pacman -S libnetfilter_queue
I compiled a little bit of C for my test.
netfil.c
Code:
#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>
#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);
nest = mnl_attr_nest_start(nlh, NFQA_CT);
mnl_attr_put_u32(nlh, CTA_MARK, htonl(42));
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]);
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);
if (attr[NFQA_HWADDR]) {
struct nfqnl_msg_packet_hw *hw = mnl_attr_get_payload(attr[NFQA_HWADDR]);
unsigned int hwlen = ntohs(hw->hw_addrlen);
const unsigned char *addr = hw->hw_addr;
unsigned int i;
printf(", hwaddr %02x", addr[0]);
for (i = 1; i < hwlen; i++) {
if (i >= sizeof(hw->hw_addr)) {
printf("[truncated]");
break;
}
printf(":%02x", (unsigned char)addr[i]);
}
printf(" len %u", hwlen);
}
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;
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);
}
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;
}
//Compile
//gcc netfil.c -g3 -ggdb -Wall -lmnl -lnetfilter_queue -o nfil
I made an iptables rule to give it packets.(Use your own interface)
Code:
iptables -A INPUT -i enp2s0 -j NFQUEUE --queue-num 0
You can cancel that with.
Code:
iptables -D INPUT -i enp2s0 -j NFQUEUE --queue-num 0
And that I ran with
Pinged google and was able to catch packets.
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