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