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
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
|
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <signal.h>
#include <unistd.h>
#include "domain2name.c" // this is from http://git.sijanec.eu/sijanec/dnsfind
enum type {
A = 1,
Ns,
Md,
Mf,
Cname,
Soa,
Mb,
M,
Mr,
Null,
Wks,
Ptr,
Hinfo,
Minfo,
Mx,
Txt
};
enum class {
In = 1,
Cs,
Ch,
He,
Any = 255
};
#define RESPONSE (1 << 15)
#define QUESTION (0 << 15)
#define QUERY (0 << 11)
#define IQUERY (1 << 11)
#define STATUS (1 << 12)
#define AA (1 << 10)
#define TC (1 << 9)
#define RD (1 << 8)
#define RA (1 << 7)
#define SUCCESS (0 << 0)
#define FORMAT_ERROR (1 << 0)
#define SERVFAIL (1 << 1)
#define NXDOMAIN (FORMAT_ERROR | SERVFAIL)
#define NI (1 << 2)
#define FORBIDDEN (NXDOMAIN | FORMAT_ERROR)
struct header {
uint16_t xid __attribute__((packed));
uint16_t flags __attribute__((packed));
uint16_t qdcount __attribute__((packed));
uint16_t ancount __attribute__((packed));
uint16_t nscount __attribute__((packed));
uint16_t arcount __attribute__((packed));
char data[]; /* ignored for char[] */
} __attribute__((packed));
struct rr { /* name is omitted, first byte of struct is first byte of type */
uint16_t type __attribute__((packed));
uint16_t class __attribute__((packed));
uint32_t ttl __attribute__((packed));
uint16_t len __attribute__((packed));
char data[]; /* ignored for char[] */
} __attribute__((packed));
struct question {
uint16_t type __attribute__((packed));
uint16_t class __attribute__((packed));
} __attribute__((packed));
enum dns_loglevel {
DNS_DEBUG,
DNS_INFO,
DNS_WARN,
DNS_ERROR
};
typedef void (* dns_log_handler) (void * const, const enum dns_loglevel, const char * const, const char * const);
struct dns {
int fd;
char * domain; // this is as it appears in the packet
dns_log_handler log_handler;
void * log_userdata;
struct sockaddr_in sockaddr;
};
typedef struct dns dns;
static void dns_default_log_handler (void * const u __attribute__((unused)),
const enum dns_loglevel l, const char * a, const char * m) {
char * n = "unspec";
switch (l) {
case DNS_DEBUG:
n = "DEBUG";
break;
case DNS_INFO:
n = "INFO";
break;
case DNS_WARN:
n = "WARN";
break;
case DNS_ERROR:
n = "ERROR";
break;
}
fprintf(stderr, "%s %s %s\n", n, a, m);
}
struct dns * dns_init (void) {
struct dns * dns = calloc(1, sizeof(struct dns));
if (!dns)
return NULL;
dns->fd = -1;
dns->domain = strdup(" call dns_set_domain to set the domain");
dns->domain[0] = strlen(dns->domain)-1;
dns->log_handler = dns_default_log_handler;
dns->sockaddr.sin_family = AF_INET;
dns->sockaddr.sin_port = htons(53);
dns->sockaddr.sin_addr.s_addr = INADDR_ANY;
return dns;
}
static void dns_set_domain (struct dns * dns, const char * domain) { // static functions are
int required = domain2name_len(domain, strlen(domain)); // visible inside the same
if (required <= 0) // translation unit - they
return; // are visible across
free(dns->domain); // included files
domain2name((dns->domain = malloc(required)), domain, strlen(domain));
}
static void dns_set_log_handler (struct dns * dns, dns_log_handler log_handler) {
if (!log_handler)
log_handler = dns_default_log_handler;
dns->log_handler = log_handler;
}
static void dns_set_log_userdata (struct dns * dns, void * log_userdata) {
dns->log_userdata = log_userdata;
}
static void dns_set_port (struct dns * dns, int port) {
dns->sockaddr.sin_port = htons(port);
}
static void dns_set_ip (struct dns * dns, const char * ip) {
if (!ip) {
dns->sockaddr.sin_addr.s_addr = INADDR_ANY;
return;
}
inet_aton(ip, &dns->sockaddr.sin_addr);
}
static void dns_run_once (struct dns * dns) {
#define BUFLEN 4096
char buf[BUFLEN];
if (dns->fd == -1) {
if ((dns->fd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) == -1) {
sprintf(buf, "socket failed with %s", strerror(errno));
dns->log_handler(dns->log_userdata, DNS_ERROR, "dns", buf);
return;
}
int ž = 1;
if (setsockopt(dns->fd, SOL_SOCKET, SO_BROADCAST, &ž, sizeof(ž)) == -1) {
sprintf(buf, "setsockopt failed with %s", strerror(errno));
dns->log_handler(dns->log_userdata, DNS_ERROR, "dns", buf);
close(dns->fd);
dns->fd = -1;
return;
}
if (bind(dns->fd, (struct sockaddr *) &dns->sockaddr, sizeof(struct sockaddr))) {
sprintf(buf, "bind failed with %s", strerror(errno));
dns->log_handler(dns->log_userdata, DNS_ERROR, "dns", buf);
close(dns->fd);
dns->fd = -1;
return;
}
}
struct sockaddr_in sender;
socklen_t sendl = sizeof sender;
int size = recvfrom(dns->fd, buf, 65535, MSG_DONTWAIT, (struct sockaddr *) &sender, &sendl);
if (size == -1) {
if (errno != EWOULDBLOCK) {
sprintf(buf, "recvfrom failed with %s", strerror(errno));
dns->log_handler(dns->log_userdata, DNS_ERROR, "dns", buf);
close(dns->fd);
dns->fd = -1;
return;
}
return;
}
struct header * header = (struct header *) buf; // time for some overwriting
header->flags = htons(RESPONSE | QUERY | AA | SUCCESS);
header->ancount = htons(1); // we keep question number intact, as we send all qs back
header->nscount = 0;
header->arcount = 0;
buf[BUFLEN-1] = '\0'; // strstr and strlen on untrusted data!
char * ouranswerisat = memmem(buf, size, "in-addr", strlen("in-addr"));
if (!ouranswerisat) {
dns->log_handler(dns->log_userdata, DNS_INFO, "dns",
"received request without 'in-addr' string ... weird.");
return;
}
ouranswerisat += 17;
struct rr * rr = (struct rr *) (ouranswerisat + strlen(header->data) + 1);
if (ouranswerisat + strlen(header->data) + 1 + sizeof(struct rr)
+ strlen(dns->domain) + 1 >= buf + BUFLEN) {
dns->log_handler(dns->log_userdata, DNS_WARN, "dns", "sent packet would be to big");
return;
}
strcpy(ouranswerisat, header->data);
rr->type = htons(Ptr);
rr->class = htons(In);
rr->ttl = 0;
rr->len = htons(strlen(dns->domain)+1);
strcpy(rr->data, dns->domain);
int len = rr->data - buf + strlen(dns->domain) + 1;
if (sendto(dns->fd, buf, len, 0, (struct sockaddr *) &sender, sizeof(sender)) == -1) {
sprintf(buf, "sendto failed with %s", strerror(errno));
dns->log_handler(dns->log_userdata, DNS_ERROR, "dns", buf);
close(dns->fd);
dns->fd = -1;
return;
}
char dst[INET_ADDRSTRLEN];
const char * resp = inet_ntop(AF_INET, &sender.sin_addr, dst, INET_ADDRSTRLEN);
sprintf(buf, "successfully sent DNS reply to %s", resp ? resp : "[inet_ntop failed]");
dns->log_handler(dns->log_userdata, DNS_ERROR, "dns", buf);
}
static void dns_free (struct dns * dns) {
if (!dns)
return;
if (dns->fd != -1)
close (dns->fd);
free(dns->domain);
free(dns);
}
#if IX_DNS_MAIN
int shouldexit = 0;
void handler (int signal __attribute__((unused))) {
shouldexit++;
}
int main (int argc, char ** argv) {
if (argc != 1+1) {
fprintf(stderr, "usage: %s respond.to.ptr.with.this.domain.\n", argv[0]);
return 1;
}
signal(SIGINT, handler);
signal(SIGTERM, handler);
dns * dns = dns_init();
dns_set_domain(dns, argv[1]);
while (!shouldexit) {
dns_run_once(dns);
}
dns_free(dns);
}
#endif
|
