1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
| #include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <errno.h>
#include <string.h>
#include <netinet/in.h>
#include <linux/ip.h>
#include <linux/udp.h>
#include <linux/tcp.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <linux/netfilter.h>
#include <libnetfilter_queue/libnetfilter_queue.h>
#include <libnetfilter_queue/libnetfilter_queue_udp.h>
#include <libnetfilter_queue/libnetfilter_queue_ipv4.h>
#define QUEUE_NUM 10010
static uint16_t checksum(uint32_t sum, uint16_t *buf, int size)
{
while (size > 1) {
sum += *buf++;
size -= sizeof(uint16_t);
}
if (size)
sum += *(uint8_t *)buf;
sum = (sum >> 16) + (sum & 0xffff);
sum += (sum >>16);
return (uint16_t)(~sum);
}
static uint16_t checksum_tcpudp_ipv4(struct iphdr *iph)
{
uint32_t sum = 0;
uint32_t iph_len = iph->ihl*4;
uint32_t len = ntohs(iph->tot_len) - iph_len;
uint8_t *payload = (uint8_t *)iph + iph_len;
sum += (iph->saddr >> 16) & 0xFFFF;
sum += (iph->saddr) & 0xFFFF;
sum += (iph->daddr >> 16) & 0xFFFF;
sum += (iph->daddr) & 0xFFFF;
sum += htons(iph->protocol);
sum += htons(len);
return checksum(sum, (uint16_t *)payload, len);
}
static void udp_compute_checksum_ipv4(struct udphdr *udph, struct iphdr *iph)
{
udph->check = 0;
udph->check = checksum_tcpudp_ipv4(iph);
}
int cb(struct nfq_q_handle *qh, struct nfgenmsg *nfmsg, struct nfq_data *nfad, void *data) {
uint32_t id;
struct nfqnl_msg_packet_hdr *ph;
unsigned char *payload;
int r;
struct iphdr *iph;
struct udphdr *udph;
struct tcphdr *tcph;
char saddr_str[16];
char daddr_str[16];
struct in_addr tmp_in_addr;
ph = nfq_get_msg_packet_hdr(nfad);
if (ph) {
id = ntohl(ph->packet_id);
r = nfq_get_payload(nfad, &payload);
if (r >= sizeof(*iph)) {
iph = (struct iphdr *)payload;
tmp_in_addr.s_addr = iph->saddr;
strcpy(saddr_str, inet_ntoa(tmp_in_addr));
tmp_in_addr.s_addr = iph->daddr;
strcpy(daddr_str, inet_ntoa(tmp_in_addr));
if (iph->protocol == IPPROTO_UDP) {
if (iph->ihl * 4 + sizeof(*udph) <= r) {
udph = (struct udphdr *)(payload + iph->ihl * 4);
if (ntohs(udph->dest) == 10010) {
if (iph->ihl * 4 + sizeof(*udph) < r && ntohs(iph->tot_len) - iph->ihl * 4 == ntohs(udph->len) && ntohs(udph->len) - sizeof(*udph) > 0) {
int offset = iph->ihl * 4 + sizeof(*udph);
memset(payload + offset, 'h', ntohs(udph->len) - sizeof(*udph));
memset(payload + iph->ihl * 4 + ntohs(udph->len) - 1, '\n', 1);
udp_compute_checksum_ipv4(udph, iph);
printf("ACCEPT & modified protocol:udp %s:%u -> %s:%u\n", saddr_str, ntohs(udph->source), daddr_str, ntohs(udph->dest));
} else {
printf("ACCEPT & !modified protocol:udp %s:%u -> %s:%u\n", saddr_str, ntohs(udph->source), daddr_str, ntohs(udph->dest));
}
nfq_set_verdict(qh, id, NF_ACCEPT, r, payload);
} else if (ntohs(udph->dest) == 10086) {
printf("DROP protocol:udp %s:%u -> %s:%u\n", saddr_str, ntohs(udph->source), daddr_str, ntohs(udph->dest));
nfq_set_verdict(qh, id, NF_DROP, 0, NULL);
} else {
printf("ACCEPT protocol:udp %s:%u -> %s:%u\n", saddr_str, ntohs(udph->source), daddr_str, ntohs(udph->dest));
nfq_set_verdict(qh, id, NF_ACCEPT, 0, NULL);
}
} else {
printf("ACCEPT protocol:udp %s -> %s\n", saddr_str, daddr_str);
nfq_set_verdict(qh, id, NF_ACCEPT, 0, NULL);
}
} else if (iph->protocol == IPPROTO_TCP) {
if (iph->ihl * 4 + sizeof(*tcph) <= r) {
tcph = (struct tcphdr *)(payload + iph->ihl *4);
printf("ACCEPT protocol:tcp %s:%u -> %s:%u\n", saddr_str, ntohs(tcph->source), daddr_str, ntohs(tcph->dest));
nfq_set_verdict(qh, id, NF_ACCEPT, 0, NULL);
} else {
printf("ACCEPT protocol:tcp %s -> %s\n", saddr_str, daddr_str);
nfq_set_verdict(qh, id, NF_ACCEPT, 0, NULL);
}
} else {
printf("ACCEPT protocol:%d %s -> %s\n", iph->protocol, saddr_str, daddr_str);
nfq_set_verdict(qh, id, NF_ACCEPT, 0, NULL);
}
} else {
printf("ACCEPT unknown protocol\n");
nfq_set_verdict(qh, id, NF_ACCEPT, 0, NULL);
}
}
return 0;
}
int main() {
struct nfq_handle *h;
struct nfq_q_handle *qh;
int r;
char buf[10240];
h = nfq_open();
if (h == NULL) {
perror("nfq_open error");
goto end;
}
if (nfq_unbind_pf(h, AF_INET) != 0) {
perror("nfq_unbind_pf error");
goto end;
}
if (nfq_bind_pf(h, AF_INET) != 0) {
perror("nfq_bind_pf error");
goto end;
}
qh = nfq_create_queue(h, QUEUE_NUM, &cb, NULL);
if (qh == NULL) {
perror("nfq_create_queue error");
goto end;
}
if (nfq_set_mode(qh, NFQNL_COPY_PACKET, 0xffff) != 0) {
perror("nfq_set_mod error");
goto end;
}
while(1) {
r = recv(nfq_fd(h), buf, sizeof(buf), 0);
if (r == 0) {
printf("recv return 0. exit");
break;
} else if (r < 0) {
perror("recv error");
break;
} else {
nfq_handle_packet(h, buf, r);
}
}
end:
if (qh) nfq_destroy_queue(qh);
if (h) nfq_close(h);
return 0;
}
|