libnetfilter_queue 1.0.5
nf-queue.c
1#include <errno.h>
2#include <stdio.h>
3#include <stdlib.h>
4#include <unistd.h>
5#include <string.h>
6#include <time.h>
7#include <arpa/inet.h>
8
9#include <libmnl/libmnl.h>
10#include <linux/netfilter.h>
11#include <linux/netfilter/nfnetlink.h>
12
13#include <linux/types.h>
14#include <linux/netfilter/nfnetlink_queue.h>
15
16#include <libnetfilter_queue/libnetfilter_queue.h>
17
18/* only for NFQA_CT, not needed otherwise: */
19#include <linux/netfilter/nfnetlink_conntrack.h>
20
21static struct mnl_socket *nl;
22
23static void
24nfq_send_verdict(int queue_num, uint32_t id)
25{
26 char buf[MNL_SOCKET_BUFFER_SIZE];
27 struct nlmsghdr *nlh;
28 struct nlattr *nest;
29
30 nlh = nfq_nlmsg_put(buf, NFQNL_MSG_VERDICT, queue_num);
31 nfq_nlmsg_verdict_put(nlh, id, NF_ACCEPT);
32
33 /* example to set the connmark. First, start NFQA_CT section: */
34 nest = mnl_attr_nest_start(nlh, NFQA_CT);
35
36 /* then, add the connmark attribute: */
37 mnl_attr_put_u32(nlh, CTA_MARK, htonl(42));
38 /* more conntrack attributes, e.g. CTA_LABELS could be set here */
39
40 /* end conntrack section */
41 mnl_attr_nest_end(nlh, nest);
42
43 if (mnl_socket_sendto(nl, nlh, nlh->nlmsg_len) < 0) {
44 perror("mnl_socket_send");
45 exit(EXIT_FAILURE);
46 }
47}
48
49static int queue_cb(const struct nlmsghdr *nlh, void *data)
50{
51 struct nfqnl_msg_packet_hdr *ph = NULL;
52 struct nlattr *attr[NFQA_MAX+1] = {};
53 uint32_t id = 0, skbinfo;
54 struct nfgenmsg *nfg;
55 uint16_t plen;
56
57 if (nfq_nlmsg_parse(nlh, attr) < 0) {
58 perror("problems parsing");
59 return MNL_CB_ERROR;
60 }
61
62 nfg = mnl_nlmsg_get_payload(nlh);
63
64 if (attr[NFQA_PACKET_HDR] == NULL) {
65 fputs("metaheader not set\n", stderr);
66 return MNL_CB_ERROR;
67 }
68
69 ph = mnl_attr_get_payload(attr[NFQA_PACKET_HDR]);
70
71 plen = mnl_attr_get_payload_len(attr[NFQA_PAYLOAD]);
72 /* void *payload = mnl_attr_get_payload(attr[NFQA_PAYLOAD]); */
73
74 skbinfo = attr[NFQA_SKB_INFO] ? ntohl(mnl_attr_get_u32(attr[NFQA_SKB_INFO])) : 0;
75
76 if (attr[NFQA_CAP_LEN]) {
77 uint32_t orig_len = ntohl(mnl_attr_get_u32(attr[NFQA_CAP_LEN]));
78 if (orig_len != plen)
79 printf("truncated ");
80 }
81
82 if (skbinfo & NFQA_SKB_GSO)
83 printf("GSO ");
84
85 id = ntohl(ph->packet_id);
86 printf("packet received (id=%u hw=0x%04x hook=%u, payload len %u",
87 id, ntohs(ph->hw_protocol), ph->hook, plen);
88
89 /*
90 * ip/tcp checksums are not yet valid, e.g. due to GRO/GSO.
91 * The application should behave as if the checksums are correct.
92 *
93 * If these packets are later forwarded/sent out, the checksums will
94 * be corrected by kernel/hardware.
95 */
96 if (skbinfo & NFQA_SKB_CSUMNOTREADY)
97 printf(", checksum not ready");
98 puts(")");
99
100 nfq_send_verdict(ntohs(nfg->res_id), id);
101
102 return MNL_CB_OK;
103}
104
105int main(int argc, char *argv[])
106{
107 char *buf;
108 /* largest possible packet payload, plus netlink data overhead: */
109 size_t sizeof_buf = 0xffff + (MNL_SOCKET_BUFFER_SIZE/2);
110 struct nlmsghdr *nlh;
111 int ret;
112 unsigned int portid, queue_num;
113
114 if (argc != 2) {
115 printf("Usage: %s [queue_num]\n", argv[0]);
116 exit(EXIT_FAILURE);
117 }
118 queue_num = atoi(argv[1]);
119
120 nl = mnl_socket_open(NETLINK_NETFILTER);
121 if (nl == NULL) {
122 perror("mnl_socket_open");
123 exit(EXIT_FAILURE);
124 }
125
126 if (mnl_socket_bind(nl, 0, MNL_SOCKET_AUTOPID) < 0) {
127 perror("mnl_socket_bind");
128 exit(EXIT_FAILURE);
129 }
130 portid = mnl_socket_get_portid(nl);
131
132 buf = malloc(sizeof_buf);
133 if (!buf) {
134 perror("allocate receive buffer");
135 exit(EXIT_FAILURE);
136 }
137
138 nlh = nfq_nlmsg_put(buf, NFQNL_MSG_CONFIG, queue_num);
139 nfq_nlmsg_cfg_put_cmd(nlh, AF_INET, NFQNL_CFG_CMD_BIND);
140
141 if (mnl_socket_sendto(nl, nlh, nlh->nlmsg_len) < 0) {
142 perror("mnl_socket_send");
143 exit(EXIT_FAILURE);
144 }
145
146 nlh = nfq_nlmsg_put(buf, NFQNL_MSG_CONFIG, queue_num);
147 nfq_nlmsg_cfg_put_params(nlh, NFQNL_COPY_PACKET, 0xffff);
148
149 mnl_attr_put_u32(nlh, NFQA_CFG_FLAGS, htonl(NFQA_CFG_F_GSO));
150 mnl_attr_put_u32(nlh, NFQA_CFG_MASK, htonl(NFQA_CFG_F_GSO));
151
152 if (mnl_socket_sendto(nl, nlh, nlh->nlmsg_len) < 0) {
153 perror("mnl_socket_send");
154 exit(EXIT_FAILURE);
155 }
156
157 /* ENOBUFS is signalled to userspace when packets were lost
158 * on kernel side. In most cases, userspace isn't interested
159 * in this information, so turn it off.
160 */
161 ret = 1;
162 mnl_socket_setsockopt(nl, NETLINK_NO_ENOBUFS, &ret, sizeof(int));
163
164 for (;;) {
165 ret = mnl_socket_recvfrom(nl, buf, sizeof_buf);
166 if (ret == -1) {
167 perror("mnl_socket_recvfrom");
168 exit(EXIT_FAILURE);
169 }
170
171 ret = mnl_cb_run(buf, ret, 0, portid, queue_cb, NULL);
172 if (ret < 0){
173 perror("mnl_cb_run");
174 exit(EXIT_FAILURE);
175 }
176 }
177
178 mnl_socket_close(nl);
179
180 return 0;
181}
void nfq_nlmsg_cfg_put_params(struct nlmsghdr *nlh, uint8_t mode, int range)
Definition nlmsg.c:182
void nfq_nlmsg_cfg_put_cmd(struct nlmsghdr *nlh, uint16_t pf, uint8_t cmd)
Definition nlmsg.c:166
void nfq_nlmsg_verdict_put(struct nlmsghdr *nlh, int id, int verdict)
Definition nlmsg.c:72
struct nlmsghdr * nfq_nlmsg_put(char *buf, int type, uint32_t queue_num)
Definition nlmsg.c:283
int nfq_nlmsg_parse(const struct nlmsghdr *nlh, struct nlattr **attr)
Definition nlmsg.c:269