about summary refs log tree commit diff
path: root/src/network/lookup_name.c
blob: c93263a9d5542918f9462d41448b9756d92adc39 (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
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
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <net/if.h>
#include <arpa/inet.h>
#include <ctype.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <unistd.h>
#include <pthread.h>
#include <errno.h>
#include <resolv.h>
#include "lookup.h"
#include "stdio_impl.h"
#include "syscall.h"

static int is_valid_hostname(const char *host)
{
	const unsigned char *s;
	if (strnlen(host, 255)-1 >= 254 || mbstowcs(0, host, 0) == -1) return 0;
	for (s=(void *)host; *s>=0x80 || *s=='.' || *s=='-' || isalnum(*s); s++);
	return !*s;
}

static int name_from_null(struct address buf[static 2], const char *name, int family, int flags)
{
	int cnt = 0;
	if (name) return 0;
	if (flags & AI_PASSIVE) {
		if (family != AF_INET6)
			buf[cnt++] = (struct address){ .family = AF_INET };
		if (family != AF_INET)
			buf[cnt++] = (struct address){ .family = AF_INET6 };
	} else {
		if (family != AF_INET6)
			buf[cnt++] = (struct address){ .family = AF_INET, .addr = { 127,0,0,1 } };
		if (family != AF_INET)
			buf[cnt++] = (struct address){ .family = AF_INET6, .addr = { [15] = 1 } };
	}
	return cnt;
}

static int name_from_numeric(struct address buf[static 1], const char *name, int family)
{
	return __lookup_ipliteral(buf, name, family);
}

static int name_from_hosts(struct address buf[static MAXADDRS], char canon[static 256], const char *name, int family)
{
	char line[512];
	size_t l = strlen(name);
	int cnt = 0, badfam = 0;
	unsigned char _buf[1032];
	FILE _f, *f = __fopen_rb_ca("/etc/hosts", &_f, _buf, sizeof _buf);
	if (!f) switch (errno) {
	case ENOENT:
	case ENOTDIR:
	case EACCES:
		return 0;
	default:
		return EAI_SYSTEM;
	}
	while (fgets(line, sizeof line, f) && cnt < MAXADDRS) {
		char *p, *z;

		if ((p=strchr(line, '#'))) *p++='\n', *p=0;
		for(p=line+1; (p=strstr(p, name)) &&
			(!isspace(p[-1]) || !isspace(p[l])); p++);
		if (!p) continue;

		/* Isolate IP address to parse */
		for (p=line; *p && !isspace(*p); p++);
		*p++ = 0;
		switch (name_from_numeric(buf+cnt, line, family)) {
		case 1:
			cnt++;
			break;
		case 0:
			continue;
		default:
			badfam = EAI_NONAME;
			continue;
		}

		/* Extract first name as canonical name */
		for (; *p && isspace(*p); p++);
		for (z=p; *z && !isspace(*z); z++);
		*z = 0;
		if (is_valid_hostname(p)) memcpy(canon, p, z-p+1);
	}
	__fclose_ca(f);
	return cnt ? cnt : badfam;
}

struct dpc_ctx {
	struct address *addrs;
	char *canon;
	int cnt;
};

#define RR_A 1
#define RR_CNAME 5
#define RR_AAAA 28

static int dns_parse_callback(void *c, int rr, const void *data, int len, const void *packet)
{
	char tmp[256];
	struct dpc_ctx *ctx = c;
	if (ctx->cnt >= MAXADDRS) return -1;
	switch (rr) {
	case RR_A:
		if (len != 4) return -1;
		ctx->addrs[ctx->cnt].family = AF_INET;
		ctx->addrs[ctx->cnt].scopeid = 0;
		memcpy(ctx->addrs[ctx->cnt++].addr, data, 4);
		break;
	case RR_AAAA:
		if (len != 16) return -1;
		ctx->addrs[ctx->cnt].family = AF_INET6;
		ctx->addrs[ctx->cnt].scopeid = 0;
		memcpy(ctx->addrs[ctx->cnt++].addr, data, 16);
		break;
	case RR_CNAME:
		if (__dn_expand(packet, (const unsigned char *)packet + 512,
		    data, tmp, sizeof tmp) > 0 && is_valid_hostname(tmp))
			strcpy(ctx->canon, tmp);
		break;
	}
	return 0;
}

static int name_from_dns(struct address buf[static MAXADDRS], char canon[static 256], const char *name, int family, const struct resolvconf *conf)
{
	unsigned char qbuf[2][280], abuf[2][512];
	const unsigned char *qp[2] = { qbuf[0], qbuf[1] };
	unsigned char *ap[2] = { abuf[0], abuf[1] };
	int qlens[2], alens[2];
	int i, nq = 0;
	struct dpc_ctx ctx = { .addrs = buf, .canon = canon };
	static const struct { int af; int rr; } afrr[2] = {
		{ .af = AF_INET6, .rr = RR_A },
		{ .af = AF_INET, .rr = RR_AAAA },
	};

	for (i=0; i<2; i++) {
		if (family != afrr[i].af) {
			qlens[nq] = __res_mkquery(0, name, 1, afrr[i].rr,
				0, 0, 0, qbuf[nq], sizeof *qbuf);
			if (qlens[nq] == -1)
				return EAI_NONAME;
			nq++;
		}
	}

	if (__res_msend_rc(nq, qp, qlens, ap, alens, sizeof *abuf, conf) < 0)
		return EAI_SYSTEM;

	for (i=0; i<nq; i++)
		__dns_parse(abuf[i], alens[i], dns_parse_callback, &ctx);

	if (ctx.cnt) return ctx.cnt;
	if (alens[0] < 4 || (abuf[0][3] & 15) == 2) return EAI_AGAIN;
	if ((abuf[0][3] & 15) == 0) return EAI_NONAME;
	if ((abuf[0][3] & 15) == 3) return 0;
	return EAI_FAIL;
}

static int name_from_dns_search(struct address buf[static MAXADDRS], char canon[static 256], const char *name, int family)
{
	char search[256];
	struct resolvconf conf;
	size_t l, dots;
	char *p, *z;

	if (__get_resolv_conf(&conf, search, sizeof search) < 0) return -1;

	/* Count dots, suppress search when >=ndots or name ends in
	 * a dot, which is an explicit request for global scope. */
	for (dots=l=0; name[l]; l++) if (name[l]=='.') dots++;
	if (dots >= conf.ndots || name[l-1]=='.') *search = 0;

	/* Strip final dot for canon, fail if multiple trailing dots. */
	if (name[l-1]=='.') l--;
	if (!l || name[l-1]=='.') return EAI_NONAME;

	/* This can never happen; the caller already checked length. */
	if (l >= 256) return EAI_NONAME;

	/* Name with search domain appended is setup in canon[]. This both
	 * provides the desired default canonical name (if the requested
	 * name is not a CNAME record) and serves as a buffer for passing
	 * the full requested name to name_from_dns. */
	memcpy(canon, name, l);
	canon[l] = '.';

	for (p=search; *p; p=z) {
		for (; isspace(*p); p++);
		for (z=p; *z && !isspace(*z); z++);
		if (z==p) break;
		if (z-p < 256 - l - 1) {
			memcpy(canon+l+1, p, z-p);
			canon[z-p+1+l] = 0;
			int cnt = name_from_dns(buf, canon, canon, family, &conf);
			if (cnt) return cnt;
		}
	}

	canon[l] = 0;
	return name_from_dns(buf, canon, name, family, &conf);
}

static const struct policy {
	unsigned char addr[16];
	unsigned char len, mask;
	unsigned char prec, label;
} defpolicy[] = {
	{ "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\1", 15, 0xff, 50, 0 },
	{ "\0\0\0\0\0\0\0\0\0\0\xff\xff", 11, 0xff, 35, 4 },
	{ "\x20\2", 1, 0xff, 30, 2 },
	{ "\x20\1", 3, 0xff, 5, 5 },
	{ "\xfc", 0, 0xfe, 3, 13 },
#if 0
	/* These are deprecated and/or returned to the address
	 * pool, so despite the RFC, treating them as special
	 * is probably wrong. */
	{ "", 11, 0xff, 1, 3 },
	{ "\xfe\xc0", 1, 0xc0, 1, 11 },
	{ "\x3f\xfe", 1, 0xff, 1, 12 },
#endif
	/* Last rule must match all addresses to stop loop. */
	{ "", 0, 0, 40, 1 },
};

static const struct policy *policyof(const struct in6_addr *a)
{
	int i;
	for (i=0; ; i++) {
		if (memcmp(a->s6_addr, defpolicy[i].addr, defpolicy[i].len))
			continue;
		if ((a->s6_addr[defpolicy[i].len] & defpolicy[i].mask)
		    != defpolicy[i].addr[defpolicy[i].len])
			continue;
		return defpolicy+i;
	}
}

static int labelof(const struct in6_addr *a)
{
	return policyof(a)->label;
}

static int scopeof(const struct in6_addr *a)
{
	if (IN6_IS_ADDR_MULTICAST(a)) return a->s6_addr[1] & 15;
	if (IN6_IS_ADDR_LINKLOCAL(a)) return 2;
	if (IN6_IS_ADDR_LOOPBACK(a)) return 2;
	if (IN6_IS_ADDR_SITELOCAL(a)) return 5;
	return 14;
}

static int prefixmatch(const struct in6_addr *s, const struct in6_addr *d)
{
	/* FIXME: The common prefix length should be limited to no greater
	 * than the nominal length of the prefix portion of the source
	 * address. However the definition of the source prefix length is
	 * not clear and thus this limiting is not yet implemented. */
	unsigned i;
	for (i=0; i<128 && !((s->s6_addr[i/8]^d->s6_addr[i/8])&(128>>(i%8))); i++);
	return i;
}

#define DAS_USABLE              0x40000000
#define DAS_MATCHINGSCOPE       0x20000000
#define DAS_MATCHINGLABEL       0x10000000
#define DAS_PREC_SHIFT          20
#define DAS_SCOPE_SHIFT         16
#define DAS_PREFIX_SHIFT        8
#define DAS_ORDER_SHIFT         0

static int addrcmp(const void *_a, const void *_b)
{
	const struct address *a = _a, *b = _b;
	return b->sortkey - a->sortkey;
}

int __lookup_name(struct address buf[static MAXADDRS], char canon[static 256], const char *name, int family, int flags)
{
	int cnt = 0, i, j;

	*canon = 0;
	if (name) {
		/* reject empty name and check len so it fits into temp bufs */
		size_t l = strnlen(name, 255);
		if (l-1 >= 254)
			return EAI_NONAME;
		memcpy(canon, name, l+1);
	}

	/* Procedurally, a request for v6 addresses with the v4-mapped
	 * flag set is like a request for unspecified family, followed
	 * by filtering of the results. */
	if (flags & AI_V4MAPPED) {
		if (family == AF_INET6) family = AF_UNSPEC;
		else flags -= AI_V4MAPPED;
	}

	/* Try each backend until there's at least one result. */
	cnt = name_from_null(buf, name, family, flags);
	if (!cnt) cnt = name_from_numeric(buf, name, family);
	if (!cnt && !(flags & AI_NUMERICHOST)) {
		cnt = name_from_hosts(buf, canon, name, family);
		if (!cnt) cnt = name_from_dns_search(buf, canon, name, family);
	}
	if (cnt<=0) return cnt ? cnt : EAI_NONAME;

	/* Filter/transform results for v4-mapped lookup, if requested. */
	if (flags & AI_V4MAPPED) {
		if (!(flags & AI_ALL)) {
			/* If any v6 results exist, remove v4 results. */
			for (i=0; i<cnt && buf[i].family != AF_INET6; i++);
			if (i<cnt) {
				for (j=0; i<cnt; i++) {
					if (buf[i].family == AF_INET6)
						buf[j++] = buf[i];
				}
				cnt = i = j;
			}
		}
		/* Translate any remaining v4 results to v6 */
		for (i=0; i<cnt; i++) {
			if (buf[i].family != AF_INET) continue;
			memcpy(buf[i].addr+12, buf[i].addr, 4);
			memcpy(buf[i].addr, "\0\0\0\0\0\0\0\0\0\0\xff\xff", 12);
			buf[i].family = AF_INET6;
		}
	}

	/* No further processing is needed if there are fewer than 2
	 * results or if there are only IPv4 results. */
	if (cnt<2 || family==AF_INET) return cnt;
	for (i=0; i<cnt; i++) if (buf[i].family != AF_INET) break;
	if (i==cnt) return cnt;

	int cs;
	pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);

	/* The following implements a subset of RFC 3484/6724 destination
	 * address selection by generating a single 31-bit sort key for
	 * each address. Rules 3, 4, and 7 are omitted for having
	 * excessive runtime and code size cost and dubious benefit.
	 * So far the label/precedence table cannot be customized. */
	for (i=0; i<cnt; i++) {
		int family = buf[i].family;
		int key = 0;
		struct sockaddr_in6 sa6 = { 0 }, da6 = {
			.sin6_family = AF_INET6,
			.sin6_scope_id = buf[i].scopeid,
			.sin6_port = 65535
		};
		struct sockaddr_in sa4 = { 0 }, da4 = {
			.sin_family = AF_INET,
			.sin_port = 65535
		};
		void *sa, *da;
		socklen_t salen, dalen;
		if (family == AF_INET6) {
			memcpy(da6.sin6_addr.s6_addr, buf[i].addr, 16);
			da = &da6; dalen = sizeof da6;
			sa = &sa6; salen = sizeof sa6;
		} else {
			memcpy(sa6.sin6_addr.s6_addr,
				"\0\0\0\0\0\0\0\0\0\0\xff\xff", 12);
			memcpy(da6.sin6_addr.s6_addr+12, buf[i].addr, 4);
			memcpy(da6.sin6_addr.s6_addr,
				"\0\0\0\0\0\0\0\0\0\0\xff\xff", 12);
			memcpy(da6.sin6_addr.s6_addr+12, buf[i].addr, 4);
			memcpy(&da4.sin_addr, buf[i].addr, 4);
			da = &da4; dalen = sizeof da4;
			sa = &sa4; salen = sizeof sa4;
		}
		const struct policy *dpolicy = policyof(&da6.sin6_addr);
		int dscope = scopeof(&da6.sin6_addr);
		int dlabel = dpolicy->label;
		int dprec = dpolicy->prec;
		int prefixlen = 0;
		int fd = socket(family, SOCK_DGRAM|SOCK_CLOEXEC, IPPROTO_UDP);
		if (fd >= 0) {
			if (!connect(fd, da, dalen)) {
				key |= DAS_USABLE;
				if (!getsockname(fd, sa, &salen)) {
					if (family == AF_INET) memcpy(
						sa6.sin6_addr.s6_addr+12,
						&sa4.sin_addr, 4);
					if (dscope == scopeof(&sa6.sin6_addr))
						key |= DAS_MATCHINGSCOPE;
					if (dlabel == labelof(&sa6.sin6_addr))
						key |= DAS_MATCHINGLABEL;
					prefixlen = prefixmatch(&sa6.sin6_addr,
						&da6.sin6_addr);
				}
			}
			close(fd);
		}
		key |= dprec << DAS_PREC_SHIFT;
		key |= (15-dscope) << DAS_SCOPE_SHIFT;
		key |= prefixlen << DAS_PREFIX_SHIFT;
		key |= (MAXADDRS-i) << DAS_ORDER_SHIFT;
		buf[i].sortkey = key;
	}
	qsort(buf, cnt, sizeof *buf, addrcmp);

	pthread_setcancelstate(cs, 0);

	return cnt;
}