summaryrefslogtreecommitdiff
path: root/src/network/__dns.c
blob: 73ec422d8882bd9cfc51e276c85dcab949ffe59e (plain) (blame)
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
#include <stdint.h>
#include <netdb.h>
#include <stdio.h>
#include <fcntl.h>
#include <limits.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/select.h>
#include <sys/time.h>
#include <netinet/in.h>
#include <time.h>
#include <ctype.h>
#include <unistd.h>
#include "__dns.h"
#include "stdio_impl.h"

#define TIMEOUT 5
#define RETRY 1
#define PACKET_MAX 512
#define PTR_MAX (64 + sizeof ".in-addr.arpa")

int __dns_doqueries(unsigned char *dest, const char *name, int *rr, int rrcnt)
{
	time_t t0 = time(0);
	int fd;
	FILE *f, _f;
	unsigned char _buf[64];
	char line[64], *s, *z;
	union {
		struct sockaddr_in sin;
		struct sockaddr_in6 sin6;
	} sa = {0}, ns[3] = {{0}};
	socklen_t sl;
	int nns;
	int family;
	unsigned char q[280] = "", *r = dest;
	int ql;
	int rlen;
	int got = 0, failed = 0;
	int errcode = EAI_AGAIN;
	int i, j;
	struct timeval tv;
	fd_set fds;
	int id;

	/* Construct query template - RR and ID will be filled later */
	if (strlen(name)-1 >= 254U) return -1;
	q[2] = q[5] = 1;
	strcpy(q+13, name);
	for (i=13; q[i]; i=j+1) {
		for (j=i; q[j] && q[j] != '.'; j++);
		if (j-i-1u > 62u) return -1;
		q[i-1] = j-i;
	}
	q[i+3] = 1;
	ql = i+4;

	/* Make a reasonably unpredictable id */
	gettimeofday(&tv, 0);
	id = tv.tv_usec + tv.tv_usec/256 & 0xffff;

	/* Get nameservers from resolv.conf, fallback to localhost */
	f = __fopen_rb_ca("/etc/resolv.conf", &_f, _buf, sizeof _buf);
	if (f) for (nns=0; nns<3 && fgets(line, sizeof line, f); ) {
		if (strncmp(line, "nameserver", 10) || !isspace(line[10]))
			continue;
		for (s=line+11; isspace(*s); s++);
		for (z=s; *z && !isspace(*z); z++);
		*z=0;
		if (__ipparse(ns+nns, family, s) < 0) continue;
		ns[nns].sin.sin_port = htons(53);
		family = ns[nns++].sin.sin_family;
		sl = family==AF_INET6 ? sizeof sa.sin6 : sizeof sa.sin;
	}
	if (f) __fclose_ca(f);
	if (!nns) {
		ns[0].sin.sin_family = AF_INET;
		ns[0].sin.sin_port = htons(53);
		nns=1;
		sl = sizeof sa.sin;
	}

	/* Get local address and open/bind a socket */
	sa.sin.sin_family = family;
	fd = socket(family, SOCK_DGRAM, 0);
	if (bind(fd, (void *)&sa, sl) < 0) {
		close(fd);
		return -1;
	}
	/* Nonblocking to work around Linux UDP select bug */
	fcntl(fd, F_SETFL, fcntl(fd, F_GETFL, 0) | O_NONBLOCK);

	/* Loop until we timeout; break early on success */
	for (; time(0)-t0 < TIMEOUT; ) {

		/* Query all configured namservers in parallel */
		for (i=0; i<rrcnt; i++) if (rr[i]) for (j=0; j<nns; j++) {
			q[0] = id+i >> 8;
			q[1] = id+i;
			q[ql-3] = rr[i];
			sendto(fd, q, ql, MSG_NOSIGNAL, (void *)&ns[j], sl);
		}

		/* Wait for a response, or until time to retry */
		FD_ZERO(&fds);
		FD_SET(fd, &fds);
		tv.tv_sec = RETRY;
		tv.tv_usec = 0;
		if (select(fd+1, &fds, 0, 0, &tv) <= 0) continue;

		/* Process any and all replies */
		while (got+failed < rrcnt && (rlen = recvfrom(fd, r, 512, 0,
			(void *)&sa, (socklen_t[1]){sl})) >= 2)
		{
			/* Ignore replies from addresses we didn't send to */
			for (i=0; i<nns; i++) if (!memcmp(ns+i, &sa, sl)) break;
			if (i==nns) continue;

			/* Compute index of the query from id */
			i = r[0]*256+r[1] - id & 0xffff;
			if ((unsigned)i >= rrcnt || !rr[i]) continue;

			/* Interpret the result code */
			switch (r[3] & 15) {
			case 0:
				got++;
				break;
			case 3:
				if (1) errcode = EAI_NONAME; else
			default:
				errcode = EAI_FAIL;
				failed++;
			}

			/* Mark this record as answered */
			rr[i] = 0;
			r += 512;
		}

		/* Check to see if we have answers to all queries */
		if (got+failed == rrcnt) break;
	}
	close(fd);

	/* Return the number of results, or an error code if none */
	if (got) return got;
	return errcode;
}

static void mkptr4(char *s, const unsigned char *ip)
{
	sprintf(s, "%d.%d.%d.%d.in-addr.arpa",
		ip[3], ip[2], ip[1], ip[0]);
}

static void mkptr6(char *s, const unsigned char *ip)
{
	static const char xdigits[] = "0123456789abcdef";
	int i;
	for (i=15; i>=0; i--) {
		*s++ = xdigits[ip[i]&15]; *s++ = '.';
		*s++ = xdigits[ip[i]>>4]; *s++ = '.';
	}
	strcpy(s, "ip6.arpa");
}

int __dns_query(unsigned char *r, const void *a, int family, int ptr)
{
	char buf[PTR_MAX];
	int rr[2], rrcnt = 1;

	if (ptr) {
		if (family == AF_INET6) mkptr6(buf, a);
		else mkptr4(buf, a);
		rr[0] = RR_PTR;
		a = buf;
	} else if (family == AF_INET6) {
		rr[0] = RR_AAAA;
	} else {
		rr[0] = RR_A;
		if (family != AF_INET) rr[rrcnt++] = RR_AAAA;
	}

	return __dns_doqueries(r, a, rr, rrcnt);
}


#define BITOP(a,b,op) \
 ((a)[(size_t)(b)/(8*sizeof *(a))] op (size_t)1<<((size_t)(b)%(8*sizeof *(a))))

static int decname(char *s, const unsigned char *b, const unsigned char *p)
{
	/* Remember jump destinations to detect loops and abort */
	size_t seen[PACKET_MAX/8/sizeof(size_t)] = { 0 };
	char *sz = s + HOST_NAME_MAX;
	const unsigned char *pz = b+512;
	for (;;) {
		if (p>=pz) return -1;
		else if (*p&0xc0) {
			int j = (p[0]&1) | p[1];
			if (BITOP(seen, j, &)) return -1;
			BITOP(seen, j, |=);
			p = b + j;
		} else if (*p) {
			if (p+*p+1>=pz || s+*p>=sz) return -1;
			memcpy(s, p+1, *p);
			s += *p+1;
			p += *p+1;
			s[-1] = *p ? '.' : 0;
		} else return 0;
	}
}

int __dns_get_rr(void *dest, size_t stride, size_t maxlen, size_t limit, const unsigned char *r, int rr, int dec)
{
	int qdcount, ancount;
	const unsigned char *p;
	char tmp[256];
	int found = 0;
	int len;

	if ((r[3]&15)) return 0;
	p = r+12;
	qdcount = r[4]*256 + r[5];
	ancount = r[6]*256 + r[7];
	if (qdcount+ancount > 64) return -1;
	while (qdcount--) {
		while (p-r < 512 && *p-1U < 127) p++;
		if (*p>193 || (*p==193 && p[1]>254) || p>r+506)
			return -1;
		p += 5 + !!*p;
	}
	while (ancount--) {
		while (p-r < 512 && *p-1U < 127) p++;
		if (*p>193 || (*p==193 && p[1]>254) || p>r+506)
			return -1;
		p += 1 + !!*p;
		len = p[8]*256 + p[9];
		if (p+len > r+512) return -1;
		if (p[1]==rr && len <= maxlen) {
			if (dec && decname(tmp, r, p+10)<0) return -1;
			if (dest && limit) {
				if (dec) strcpy(dest, tmp);
				else memcpy(dest, p+10, len);
				dest = (char *)dest + stride;
				limit--;
			}
			found++;
		}
		p += 10 + len;
	}
	return found;
}

int __dns_count_addrs(const unsigned char *r, int cnt)
{
	int found=0, res, i;
	static const int p[2][2] = { { 4, RR_A }, { 16, RR_AAAA } };

	while (cnt--) for (i=0; i<2; i++) {
		res = __dns_get_rr(0, 0, p[i][0], -1, r, p[i][1], 0);
		if (res < 0) return res;
		found += res;
		r += 512;
	}
	return found;
}