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
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
|
/* vi: set sw=4 ts=4: */
/*
* Mini DNS server implementation for busybox
*
* Copyright (C) 2005 Roberto A. Foglietta (me@roberto.foglietta.name)
* Copyright (C) 2005 Odd Arild Olsen (oao at fibula dot no)
* Copyright (C) 2003 Paul Sheer
*
* Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
*
* Odd Arild Olsen started out with the sheerdns [1] of Paul Sheer and rewrote
* it into a shape which I believe is both easier to understand and maintain.
* I also reused the input buffer for output and removed services he did not
* need. [1] http://threading.2038bug.com/sheerdns/
*
* Some bugfix and minor changes was applied by Roberto A. Foglietta who made
* the first porting of oao' scdns to busybox also.
*/
#include "busybox.h"
static const char *fileconf = "/etc/dnsd.conf";
#define LOCK_FILE "/var/run/dnsd.lock"
// Must match getopt32 call
#define OPT_daemon (option_mask32 & 0x10)
#define OPT_verbose (option_mask32 & 0x20)
//#define DEBUG 1
#define DEBUG 0
enum {
MAX_HOST_LEN = 16, // longest host name allowed is 15
IP_STRING_LEN = 18, // .xxx.xxx.xxx.xxx\0
//must be strlen('.in-addr.arpa') larger than IP_STRING_LEN
MAX_NAME_LEN = (IP_STRING_LEN + 13),
/* Cannot get bigger packets than 512 per RFC1035
In practice this can be set considerably smaller:
Length of response packet is header (12B) + 2*type(4B) + 2*class(4B) +
ttl(4B) + rlen(2B) + r (MAX_NAME_LEN =21B) +
2*querystring (2 MAX_NAME_LEN= 42B), all together 90 Byte
*/
MAX_PACK_LEN = 512 + 1,
DEFAULT_TTL = 30, // increase this when not testing?
REQ_A = 1,
REQ_PTR = 12
};
struct dns_repl { // resource record, add 0 or 1 to accepted dns_msg in resp
uint16_t rlen;
uint8_t *r; // resource
uint16_t flags;
};
struct dns_head { // the message from client and first part of response mag
uint16_t id;
uint16_t flags;
uint16_t nquer; // accepts 0
uint16_t nansw; // 1 in response
uint16_t nauth; // 0
uint16_t nadd; // 0
};
struct dns_prop {
uint16_t type;
uint16_t class;
};
struct dns_entry { // element of known name, ip address and reversed ip address
struct dns_entry *next;
char ip[IP_STRING_LEN]; // dotted decimal IP
char rip[IP_STRING_LEN]; // length decimal reversed IP
char name[MAX_HOST_LEN];
};
static struct dns_entry *dnsentry = NULL;
static uint32_t ttl = DEFAULT_TTL;
/*
* Convert host name from C-string to dns length/string.
*/
static void convname(char *a, uint8_t *q)
{
int i = (q[0] == '.') ? 0 : 1;
for (; i < MAX_HOST_LEN-1 && *q; i++, q++)
a[i] = tolower(*q);
a[0] = i - 1;
a[i] = 0;
}
/*
* Insert length of substrings instead of dots
*/
static void undot(uint8_t * rip)
{
int i = 0, s = 0;
while (rip[i])
i++;
for (--i; i >= 0; i--) {
if (rip[i] == '.') {
rip[i] = s;
s = 0;
} else s++;
}
}
/*
* Read one line of hostname/IP from file
* Returns 0 for each valid entry read, -1 at EOF
* Assumes all host names are lower case only
* Hostnames with more than one label are not handled correctly.
* Presently the dot is copied into name without
* converting to a length/string substring for that label.
*/
static int getfileentry(FILE * fp, struct dns_entry *s)
{
unsigned int a,b,c,d;
char *line, *r, *name;
restart:
line = r = xmalloc_fgets(fp);
if (!r)
return -1;
while (*r == ' ' || *r == '\t') {
r++;
if (!*r || *r == '#' || *r == '\n') {
free(line);
goto restart; /* skipping empty/blank and commented lines */
}
}
name = r;
while (*r != ' ' && *r != '\t')
r++;
*r++ = '\0';
if (sscanf(r, "%u.%u.%u.%u", &a, &b, &c, &d) != 4) {
free(line);
goto restart; /* skipping wrong lines */
}
sprintf(s->ip, "%u.%u.%u.%u", a, b, c, d);
sprintf(s->rip, ".%u.%u.%u.%u", d, c, b, a);
undot((uint8_t*)s->rip);
convname(s->name, (uint8_t*)name);
if (OPT_verbose)
fprintf(stderr, "\tname:%s, ip:%s\n", &(s->name[1]),s->ip);
free(line);
return 0;
}
/*
* Read hostname/IP records from file
*/
static void dnsentryinit(void)
{
FILE *fp;
struct dns_entry *m, *prev;
prev = dnsentry = NULL;
fp = xfopen(fileconf, "r");
while (1) {
m = xzalloc(sizeof(*m));
/*m->next = NULL;*/
if (getfileentry(fp, m))
break;
if (prev == NULL)
dnsentry = m;
else
prev->next = m;
prev = m;
}
fclose(fp);
}
/*
* Look query up in dns records and return answer if found
* qs is the query string, first byte the string length
*/
static int table_lookup(uint16_t type, uint8_t * as, uint8_t * qs)
{
int i;
struct dns_entry *d=dnsentry;
do {
#if DEBUG
char *p,*q;
q = (char *)&(qs[1]);
p = &(d->name[1]);
fprintf(stderr, "\n%s: %d/%d p:%s q:%s %d",
__FUNCTION__, (int)strlen(p), (int)(d->name[0]),
p, q, (int)strlen(q));
#endif
if (type == REQ_A) { /* search by host name */
for (i = 1; i <= (int)(d->name[0]); i++)
if (tolower(qs[i]) != d->name[i])
break;
if (i > (int)(d->name[0])) {
#if DEBUG
fprintf(stderr, " OK");
#endif
strcpy((char *)as, d->ip);
#if DEBUG
fprintf(stderr, " as:%s\n", as);
#endif
return 0;
}
} else
if (type == REQ_PTR) { /* search by IP-address */
if (!strncmp((char*)&d->rip[1], (char*)&qs[1], strlen(d->rip)-1)) {
strcpy((char *)as, d->name);
return 0;
}
}
d = d->next;
} while (d);
return -1;
}
/*
* Decode message and generate answer
*/
#define eret(s) do { fputs(s, stderr); return -1; } while (0)
static int process_packet(uint8_t * buf)
{
struct dns_head *head;
struct dns_prop *qprop;
struct dns_repl outr;
void *next, *from, *answb;
uint8_t answstr[MAX_NAME_LEN + 1];
int lookup_result, type, len, packet_len;
uint16_t flags;
answstr[0] = '\0';
head = (struct dns_head *)buf;
if (head->nquer == 0)
eret("no queries\n");
if (head->flags & 0x8000)
eret("ignoring response packet\n");
from = (void *)&head[1]; // start of query string
next = answb = from + strlen((char *)from) + 1 + sizeof(struct dns_prop); // where to append answer block
outr.rlen = 0; // may change later
outr.r = NULL;
outr.flags = 0;
qprop = (struct dns_prop *)(answb - 4);
type = ntohs(qprop->type);
// only let REQ_A and REQ_PTR pass
if (!(type == REQ_A || type == REQ_PTR)) {
goto empty_packet; /* we can't handle the query type */
}
if (ntohs(qprop->class) != 1 /* class INET */ ) {
outr.flags = 4; /* not supported */
goto empty_packet;
}
/* we only support standard queries */
if ((ntohs(head->flags) & 0x7800) != 0)
goto empty_packet;
// We have a standard query
bb_info_msg("%s", (char *)from);
lookup_result = table_lookup(type, answstr, (uint8_t*)from);
if (lookup_result != 0) {
outr.flags = 3 | 0x0400; //name do not exist and auth
goto empty_packet;
}
if (type == REQ_A) { // return an address
struct in_addr a;
if (!inet_aton((char*)answstr, &a)) {//dotted dec to long conv
outr.flags = 1; /* Frmt err */
goto empty_packet;
}
memcpy(answstr, &a.s_addr, 4); // save before a disappears
outr.rlen = 4; // uint32_t IP
}
else
outr.rlen = strlen((char *)answstr) + 1; // a host name
outr.r = answstr; // 32 bit ip or a host name
outr.flags |= 0x0400; /* authority-bit */
// we have an answer
head->nansw = htons(1);
// copy query block to answer block
len = answb - from;
memcpy(answb, from, len);
next += len;
// and append answer rr
*(uint32_t *) next = htonl(ttl);
next += 4;
*(uint16_t *) next = htons(outr.rlen);
next += 2;
memcpy(next, (void *)answstr, outr.rlen);
next += outr.rlen;
empty_packet:
flags = ntohs(head->flags);
// clear rcode and RA, set responsebit and our new flags
flags |= (outr.flags & 0xff80) | 0x8000;
head->flags = htons(flags);
head->nauth = head->nadd = htons(0);
head->nquer = htons(1);
packet_len = next - (void *)buf;
return packet_len;
}
/*
* Exit on signal
*/
static void interrupt(int x)
{
unlink(LOCK_FILE);
bb_error_msg("interrupt, exiting\n");
exit(2);
}
int dnsd_main(int argc, char **argv);
int dnsd_main(int argc, char **argv)
{
char *listen_interface = NULL;
char *sttl, *sport;
len_and_sockaddr *lsa;
int udps;
uint16_t port = 53;
uint8_t buf[MAX_PACK_LEN];
getopt32(argc, argv, "i:c:t:p:dv", &listen_interface, &fileconf, &sttl, &sport);
//if (option_mask32 & 0x1) // -i
//if (option_mask32 & 0x2) // -c
if (option_mask32 & 0x4) // -t
ttl = xatou_range(sttl, 1, 0xffffffff);
if (option_mask32 & 0x8) // -p
port = xatou_range(sttl, 1, 0xffff);
if (OPT_verbose) {
bb_info_msg("listen_interface: %s", listen_interface);
bb_info_msg("ttl: %d, port: %d", ttl, port);
bb_info_msg("fileconf: %s", fileconf);
}
if (OPT_daemon) {
//FIXME: NOMMU will NOT set LOGMODE_SYSLOG!
#ifdef BB_NOMMU
if (!re_execed)
vfork_daemon_rexec(1, 0, argv);
#else
xdaemon(1, 0);
#endif
logmode = LOGMODE_SYSLOG;
}
dnsentryinit();
signal(SIGINT, interrupt);
signal(SIGPIPE, SIG_IGN);
signal(SIGHUP, SIG_IGN);
#ifdef SIGTSTP
signal(SIGTSTP, SIG_IGN);
#endif
#ifdef SIGURG
signal(SIGURG, SIG_IGN);
#endif
lsa = xhost2sockaddr(listen_interface, port);
udps = xsocket(lsa->sa.sa_family, SOCK_DGRAM, 0);
xbind(udps, &lsa->sa, lsa->len);
// xlisten(udps, 50); - ?!! DGRAM sockets are never listened on I think?
bb_info_msg("Accepting UDP packets on %s",
xmalloc_sockaddr2dotted(&lsa->sa, lsa->len));
while (1) {
fd_set fdset;
int r;
FD_ZERO(&fdset);
FD_SET(udps, &fdset);
// Block until a message arrives
// FIXME: Fantastic. select'ing on just one fd??
// Why no just block on it doing recvfrom() ?
r = select(udps + 1, &fdset, NULL, NULL, NULL);
if (r < 0)
bb_perror_msg_and_die("select error");
if (r == 0)
bb_perror_msg_and_die("select spurious return");
/* Can this test ever be false? - yes */
if (FD_ISSET(udps, &fdset)) {
socklen_t fromlen = lsa->len;
// FIXME: need to get *DEST* address (to which of our addresses
// this query was directed), and reply from the same address.
// Or else we can exhibit usual UDP ugliness:
// [ip1.multihomed.ip2] <= query to ip1 <= peer
// [ip1.multihomed.ip2] => reply from ip2 => peer (confused)
r = recvfrom(udps, buf, sizeof(buf), 0, &lsa->sa, &fromlen);
if (OPT_verbose)
bb_info_msg("Got UDP packet");
if (r < 12 || r > 512) {
bb_error_msg("invalid packet size");
continue;
}
if (r <= 0)
continue;
r = process_packet(buf);
if (r <= 0)
continue;
sendto(udps, buf, r, 0, &lsa->sa, fromlen);
}
}
}
|