xref: /illumos-gate/usr/src/lib/libresolv/res_gethost.c (revision bd0e95e605fff368075e869efe6d31ebe471ea49)
1 /*
2  * Copyright 2015 Gary Mills
3  * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
4  * Use is subject to license terms.
5  */
6 
7 /*
8  * Copyright (c) 1985, 1988 Regents of the University of California.
9  * All rights reserved.
10  *
11  * Redistribution and use in source and binary forms are permitted
12  * provided that this notice is preserved and that due credit is given
13  * to the University of California at Berkeley. The name of the University
14  * may not be used to endorse or promote products derived from this
15  * software without specific prior written permission. This software
16  * is provided ``as is'' without express or implied warranty.
17  *
18  */
19 
20 #include <sys/param.h>
21 #include <sys/socket.h>
22 #include <netinet/in.h>
23 #include <ctype.h>
24 #include <netdb.h>
25 #include <stdio.h>
26 #include <errno.h>
27 #include <string.h>
28 #include <arpa/inet.h>
29 #include <arpa/nameser.h>
30 #include <resolv.h>
31 #include <syslog.h>
32 #include "crossl.h"
33 
34 /*
35  * When the name service switch calls libresolv, it doesn't want fallback
36  * to /etc/hosts, so we provide a method to turn it off.
37  */
38 static int	no_hosts_fallback = 0;
39 
40 void
__res_set_no_hosts_fallback(void)41 __res_set_no_hosts_fallback(void) {
42 	no_hosts_fallback = 1;
43 }
44 
45 static int
__res_no_hosts_fallback(void)46 __res_no_hosts_fallback(void) {
47 	return(no_hosts_fallback);
48 }
49 
50 static char *h_addr_ptrs[MAXADDRS + 1];
51 
52 static struct hostent host;
53 static char *host_aliases[MAXALIASES];
54 static char hostbuf[BUFSIZ+1];
55 static struct in_addr host_addr;
56 static char HOSTDB[] = "/etc/hosts";
57 static FILE *hostf = NULL;
58 static char hostaddr[MAXADDRS];
59 static char *host_addrs[2];
60 static int stayopen = 0;
61 static char *any();
62 
63 #if PACKETSZ > 1024
64 #define	MAXPACKET	PACKETSZ
65 #else
66 #define	MAXPACKET	1024
67 #endif
68 
69 typedef union {
70 	HEADER hdr;
71 	u_char buf[MAXPACKET];
72 } querybuf;
73 
74 static union {
75 	long al;
76 	char ac;
77 } align;
78 
79 
80 int h_errno;
81 
82 static struct hostent *
getanswer(answer,anslen,iquery)83 getanswer(answer, anslen, iquery)
84 	querybuf *answer;
85 	int anslen;
86 	int iquery;
87 {
88 	register HEADER *hp;
89 	register u_char *cp;
90 	register int n;
91 	u_char *eom;
92 	char *bp, **ap;
93 	int type, class, buflen, ancount, qdcount;
94 	int haveanswer, getclass = C_ANY;
95 	char **hap;
96 
97 	eom = answer->buf + anslen;
98 	/*
99 	 * find first satisfactory answer
100 	 */
101 	hp = &answer->hdr;
102 	ancount = ntohs(hp->ancount);
103 	qdcount = ntohs(hp->qdcount);
104 	bp = hostbuf;
105 	buflen = sizeof (hostbuf);
106 	cp = answer->buf + sizeof (HEADER);
107 	if (qdcount) {
108 		if (iquery) {
109 			if ((n = dn_expand(answer->buf, eom,
110 			    cp, (u_char *)bp, buflen)) < 0) {
111 				h_errno = NO_RECOVERY;
112 				return ((struct hostent *) NULL);
113 			}
114 			cp += n + QFIXEDSZ;
115 			host.h_name = bp;
116 			n = strlen(bp) + 1;
117 			bp += n;
118 			buflen -= n;
119 		} else
120 			cp += dn_skipname(cp, eom) + QFIXEDSZ;
121 		while (--qdcount > 0)
122 			cp += dn_skipname(cp, eom) + QFIXEDSZ;
123 	} else if (iquery) {
124 		if (hp->aa)
125 			h_errno = HOST_NOT_FOUND;
126 		else
127 			h_errno = TRY_AGAIN;
128 		return ((struct hostent *) NULL);
129 	}
130 	ap = host_aliases;
131 	host.h_aliases = host_aliases;
132 	hap = h_addr_ptrs;
133 #if BSD >= 43 || defined(h_addr)	/* new-style hostent structure */
134 	host.h_addr_list = h_addr_ptrs;
135 #endif
136 	haveanswer = 0;
137 	while (--ancount >= 0 && cp < eom && haveanswer < MAXADDRS) {
138 		if ((n = dn_expand(answer->buf, eom,
139 		    cp, (u_char *)bp, buflen)) < 0)
140 			break;
141 		cp += n;
142 		type = _getshort(cp);
143 		cp += sizeof (u_short);
144 		class = _getshort(cp);
145 		cp += sizeof (u_short) + sizeof (u_long);
146 		n = _getshort(cp);
147 		cp += sizeof (u_short);
148 		if (type == T_CNAME) {
149 			cp += n;
150 			if (ap >= &host_aliases[MAXALIASES-1])
151 				continue;
152 			*ap++ = bp;
153 			n = strlen(bp) + 1;
154 			bp += n;
155 			buflen -= n;
156 			continue;
157 		}
158 		if (iquery && type == T_PTR) {
159 			if ((n = dn_expand(answer->buf, eom,
160 			    cp, (u_char *)bp, buflen)) < 0) {
161 				cp += n;
162 				continue;
163 			}
164 			cp += n;
165 			host.h_name = bp;
166 			return (&host);
167 		}
168 		if (iquery || type != T_A) {
169 #ifdef DEBUG
170 			if (_res.options & RES_DEBUG)
171 				printf("unexpected answer type %d, size %d\n",
172 					type, n);
173 #endif
174 			cp += n;
175 			continue;
176 		}
177 		if (haveanswer) {
178 			if (n != host.h_length) {
179 				cp += n;
180 				continue;
181 			}
182 			if (class != getclass) {
183 				cp += n;
184 				continue;
185 			}
186 		} else {
187 			host.h_length = n;
188 			getclass = class;
189 			host.h_addrtype = (class == C_IN) ? AF_INET : AF_UNSPEC;
190 			if (!iquery) {
191 				host.h_name = bp;
192 				bp += strlen(bp) + 1;
193 			}
194 		}
195 
196 		bp += sizeof (align) - ((u_long)bp % sizeof (align));
197 
198 		if (bp + n >= &hostbuf[sizeof (hostbuf)]) {
199 #ifdef DEBUG
200 			if (_res.options & RES_DEBUG)
201 				printf("size (%d) too big\n", n);
202 #endif
203 			break;
204 		}
205 #ifdef SYSV
206 		memcpy((void *)(*hap++ = bp), (void *)cp, n);
207 #else
208 		bcopy(cp, *hap++ = bp, n);
209 #endif
210 		bp += n;
211 		cp += n;
212 		haveanswer++;
213 	}
214 	if (haveanswer) {
215 		*ap = NULL;
216 #if BSD >= 43 || defined(h_addr)	/* new-style hostent structure */
217 		*hap = NULL;
218 #else
219 		host.h_addr = h_addr_ptrs[0];
220 #endif
221 		return (&host);
222 	} else {
223 		h_errno = TRY_AGAIN;
224 		return ((struct hostent *) NULL);
225 	}
226 }
227 
228 static struct hostent *_gethtbyname();
229 
230 struct hostent *
res_gethostbyname(name)231 res_gethostbyname(name)
232 	char *name;
233 {
234 	querybuf buf;
235 	register char *cp;
236 	int n;
237 
238 	/*
239 	 * disallow names consisting only of digits/dots, unless
240 	 * they end in a dot.
241 	 */
242 	if (isdigit(name[0]))
243 		for (cp = name; /*EMPTY*/; ++cp) {
244 			if (!*cp) {
245 				if (*--cp == '.')
246 					break;
247 				h_errno = HOST_NOT_FOUND;
248 				return ((struct hostent *) NULL);
249 			}
250 			if (!isdigit(*cp) && *cp != '.')
251 				break;
252 		}
253 
254 	if ((n = res_search(name, C_IN, T_A, buf.buf, sizeof (buf))) < 0) {
255 #ifdef DEBUG
256 		if (_res.options & RES_DEBUG)
257 			printf("res_search failed\n");
258 #endif
259 		if (errno == ECONNREFUSED)
260 			return (_gethtbyname(name));
261 		else
262 			return ((struct hostent *) NULL);
263 	}
264 	return (getanswer(&buf, n, 0));
265 }
266 
267 static struct hostent *_gethtbyaddr();
268 
269 static struct hostent *
_getrhbyaddr(addr,len,type)270 _getrhbyaddr(addr, len, type)
271 	char *addr;
272 	int len, type;
273 {
274 	int n;
275 	querybuf buf;
276 	register struct hostent *hp;
277 	char qbuf[MAXDNAME];
278 
279 	if (type != AF_INET)
280 		return ((struct hostent *) NULL);
281 	(void) sprintf(qbuf, "%d.%d.%d.%d.in-addr.arpa",
282 		((unsigned)addr[3] & 0xff),
283 		((unsigned)addr[2] & 0xff),
284 		((unsigned)addr[1] & 0xff),
285 		((unsigned)addr[0] & 0xff));
286 	n = res_query(qbuf, C_IN, T_PTR, (u_char *)&buf, sizeof (buf));
287 	if (n < 0) {
288 #ifdef DEBUG
289 		if (_res.options & RES_DEBUG)
290 			printf("res_query failed\n");
291 #endif
292 		if (errno == ECONNREFUSED)
293 			return (_gethtbyaddr(addr, len, type));
294 		return ((struct hostent *) NULL);
295 	}
296 	hp = getanswer(&buf, n, 1);
297 	if (hp == NULL)
298 		return ((struct hostent *) NULL);
299 	hp->h_addrtype = type;
300 	hp->h_length = len;
301 	h_addr_ptrs[0] = (char *)&host_addr;
302 	h_addr_ptrs[1] = (char *)0;
303 	host_addr = *(struct in_addr *)addr;
304 	return (hp);
305 }
306 
307 /*
308  * First we get what the PTR record says, but do an extra call
309  * to gethostbyname() to make sure that someone is not trying to
310  * spoof us.  Hopefully this is not done that often, so good
311  * performance is not really an issue.
312  */
313 struct hostent *
res_gethostbyaddr(addr,len,type)314 res_gethostbyaddr(addr, len, type)
315 	char	*addr;
316 	int	len;
317 	int	type;
318 {
319 	char		**a, hbuf[MAXHOSTNAMELEN];
320 	struct hostent	*hp, *hp2;
321 
322 	if ((hp = _getrhbyaddr(addr, len, type)) == (struct hostent *)NULL)
323 		return ((struct hostent *)NULL);
324 
325 	/* hang on to what we got as an answer */
326 	(void) strcpy(hbuf, hp->h_name);
327 
328 	/* check to make sure by doing a forward query */
329 	if ((hp2 = res_gethostbyname(hbuf)) != (struct hostent *)NULL)
330 		for (a = hp2->h_addr_list; *a; a++)
331 #ifdef SYSV
332 			if (memcmp(*a, addr, hp2->h_length) == 0)
333 #else
334 			if (bcmp(*a, addr, hp2->h_length) == 0)
335 #endif
336 				return (hp2);
337 
338 	/*
339 	 * we've been spoofed, make sure to log it.
340 	 * XXX - syslog needs a security priority level.
341 	 */
342 	syslog(LOG_NOTICE, "gethostbyaddr: %s != %s", hbuf,
343 		inet_ntoa(*(struct in_addr *)addr));
344 	return ((struct hostent *)NULL);
345 }
346 
347 static void
_sethtent(int f)348 _sethtent(int f)
349 {
350 	if (__res_no_hosts_fallback()) return;
351 
352 	if (hostf == NULL)
353 		hostf = fopen(HOSTDB, "r");
354 	else
355 		rewind(hostf);
356 	stayopen |= f;
357 }
358 
359 static void
_endhtent(void)360 _endhtent(void)
361 {
362 	if (__res_no_hosts_fallback()) return;
363 
364 	if (hostf && !stayopen) {
365 		(void) fclose(hostf);
366 		hostf = NULL;
367 	}
368 }
369 
370 static struct hostent *
_gethtent()371 _gethtent()
372 {
373 	char *p;
374 	register char *cp, **q;
375 
376 	if (__res_no_hosts_fallback()) return(NULL);
377 
378 	if (hostf == NULL && (hostf = fopen(HOSTDB, "r")) == NULL)
379 		return (NULL);
380 again:
381 	if ((p = fgets(hostbuf, BUFSIZ, hostf)) == NULL)
382 		return (NULL);
383 	if (*p == '#')
384 		goto again;
385 	cp = any(p, "#\n");
386 	if (cp == NULL)
387 		goto again;
388 	*cp = '\0';
389 	cp = any(p, " \t");
390 	if (cp == NULL)
391 		goto again;
392 	*cp++ = '\0';
393 	/* THIS STUFF IS INTERNET SPECIFIC */
394 #if BSD >= 43 || defined(h_addr)	/* new-style hostent structure */
395 	host.h_addr_list = host_addrs;
396 #endif
397 	host.h_addr = hostaddr;
398 	*((u_long *)host.h_addr) = inet_addr(p);
399 	host.h_length = sizeof (u_long);
400 	host.h_addrtype = AF_INET;
401 	while (*cp == ' ' || *cp == '\t')
402 		cp++;
403 	host.h_name = cp;
404 	q = host.h_aliases = host_aliases;
405 	cp = any(cp, " \t");
406 	if (cp != NULL)
407 		*cp++ = '\0';
408 	while (cp && *cp) {
409 		if (*cp == ' ' || *cp == '\t') {
410 			cp++;
411 			continue;
412 		}
413 		if (q < &host_aliases[MAXALIASES - 1])
414 			*q++ = cp;
415 		cp = any(cp, " \t");
416 		if (cp != NULL)
417 			*cp++ = '\0';
418 	}
419 	*q = NULL;
420 	return (&host);
421 }
422 
423 static char *
any(cp,match)424 any(cp, match)
425 	register char *cp;
426 	char *match;
427 {
428 	register char *mp, c;
429 
430 	while (c = *cp) {
431 		for (mp = match; *mp; mp++)
432 			if (*mp == c)
433 				return (cp);
434 		cp++;
435 	}
436 	return ((char *)0);
437 }
438 
439 static struct hostent *
_gethtbyname(name)440 _gethtbyname(name)
441 	char *name;
442 {
443 	register struct hostent *p;
444 	register char **cp;
445 
446 	_sethtent(0);
447 	while (p = _gethtent()) {
448 		if (strcasecmp(p->h_name, name) == 0)
449 			break;
450 		for (cp = p->h_aliases; *cp != 0; cp++)
451 			if (strcasecmp(*cp, name) == 0)
452 				goto found;
453 	}
454 found:
455 	_endhtent();
456 	return (p);
457 }
458 
459 static struct hostent *
_gethtbyaddr(addr,len,type)460 _gethtbyaddr(addr, len, type)
461 	char *addr;
462 	int len, type;
463 {
464 	register struct hostent *p;
465 
466 	_sethtent(0);
467 	while (p = _gethtent())
468 #ifdef SYSV
469 		if (p->h_addrtype == type && !memcmp(p->h_addr, addr, len))
470 #else
471 		if (p->h_addrtype == type && !bcmp(p->h_addr, addr, len))
472 #endif
473 			break;
474 	_endhtent();
475 	return (p);
476 }
477