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1 | /* Copyright (C) 1993-2019 Free Software Foundation, Inc. | |
2 | This file is part of the GNU C Library. | |
3 | Contributed by David Mosberger (davidm@azstarnet.com). | |
4 | ||
5 | The GNU C Library is free software; you can redistribute it and/or | |
6 | modify it under the terms of the GNU Lesser General Public | |
7 | License as published by the Free Software Foundation; either | |
8 | version 2.1 of the License, or (at your option) any later version. | |
9 | ||
10 | The GNU C Library is distributed in the hope that it will be useful, | |
11 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
13 | Lesser General Public License for more details. | |
14 | ||
15 | You should have received a copy of the GNU Lesser General Public | |
16 | License along with the GNU C Library; if not, see | |
17 | <http://www.gnu.org/licenses/>. */ | |
18 | ||
19 | /* This file provides a Linux /etc/host.conf compatible front end to | |
20 | the various name resolvers (/etc/hosts, named, NIS server, etc.). | |
21 | Though mostly compatibly, the following differences exist compared | |
22 | to the original implementation: | |
23 | ||
24 | - line comments can appear anywhere (not just at the beginning of | |
25 | a line) | |
26 | */ | |
27 | ||
28 | #include <assert.h> | |
29 | #include <errno.h> | |
30 | #include <ctype.h> | |
31 | #include <libintl.h> | |
32 | #include <memory.h> | |
33 | #include <stdio.h> | |
34 | #include <stdio_ext.h> | |
35 | #include <stdlib.h> | |
36 | #include <string.h> | |
37 | #include <net/if.h> | |
38 | #include <sys/ioctl.h> | |
39 | #include <unistd.h> | |
40 | #include <netinet/in.h> | |
41 | #include <libc-lock.h> | |
42 | #include "ifreq.h" | |
43 | #include "res_hconf.h" | |
44 | #include <wchar.h> | |
45 | #include <atomic.h> | |
46 | ||
47 | #if IS_IN (libc) | |
48 | # define fgets_unlocked __fgets_unlocked | |
49 | #endif | |
50 | ||
51 | #define _PATH_HOSTCONF "/etc/host.conf" | |
52 | ||
53 | /* Environment vars that all user to override default behavior: */ | |
54 | #define ENV_HOSTCONF "RESOLV_HOST_CONF" | |
55 | #define ENV_TRIM_OVERR "RESOLV_OVERRIDE_TRIM_DOMAINS" | |
56 | #define ENV_TRIM_ADD "RESOLV_ADD_TRIM_DOMAINS" | |
57 | #define ENV_MULTI "RESOLV_MULTI" | |
58 | #define ENV_REORDER "RESOLV_REORDER" | |
59 | ||
60 | enum parse_cbs | |
61 | { | |
62 | CB_none, | |
63 | CB_arg_trimdomain_list, | |
64 | CB_arg_bool | |
65 | }; | |
66 | ||
67 | static const struct cmd | |
68 | { | |
69 | const char name[11]; | |
70 | uint8_t cb; | |
71 | unsigned int arg; | |
72 | } cmd[] = | |
73 | { | |
74 | {"order", CB_none, 0}, | |
75 | {"trim", CB_arg_trimdomain_list, 0}, | |
76 | {"multi", CB_arg_bool, HCONF_FLAG_MULTI}, | |
77 | {"reorder", CB_arg_bool, HCONF_FLAG_REORDER} | |
78 | }; | |
79 | ||
80 | /* Structure containing the state. */ | |
81 | struct hconf _res_hconf; | |
82 | ||
83 | /* Skip white space. */ | |
84 | static const char * | |
85 | skip_ws (const char *str) | |
86 | { | |
87 | while (isspace (*str)) ++str; | |
88 | return str; | |
89 | } | |
90 | ||
91 | ||
92 | /* Skip until whitespace, comma, end of line, or comment character. */ | |
93 | static const char * | |
94 | skip_string (const char *str) | |
95 | { | |
96 | while (*str && !isspace (*str) && *str != '#' && *str != ',') | |
97 | ++str; | |
98 | return str; | |
99 | } | |
100 | ||
101 | ||
102 | static const char * | |
103 | arg_trimdomain_list (const char *fname, int line_num, const char *args) | |
104 | { | |
105 | const char * start; | |
106 | size_t len; | |
107 | ||
108 | do | |
109 | { | |
110 | start = args; | |
111 | args = skip_string (args); | |
112 | len = args - start; | |
113 | ||
114 | if (_res_hconf.num_trimdomains >= TRIMDOMAINS_MAX) | |
115 | { | |
116 | char *buf; | |
117 | ||
118 | if (__asprintf (&buf, _("\ | |
119 | %s: line %d: cannot specify more than %d trim domains"), | |
120 | fname, line_num, TRIMDOMAINS_MAX) < 0) | |
121 | return 0; | |
122 | ||
123 | __fxprintf (NULL, "%s", buf); | |
124 | ||
125 | free (buf); | |
126 | return 0; | |
127 | } | |
128 | _res_hconf.trimdomain[_res_hconf.num_trimdomains++] = | |
129 | __strndup (start, len); | |
130 | args = skip_ws (args); | |
131 | switch (*args) | |
132 | { | |
133 | case ',': case ';': case ':': | |
134 | args = skip_ws (++args); | |
135 | if (!*args || *args == '#') | |
136 | { | |
137 | char *buf; | |
138 | ||
139 | if (__asprintf (&buf, _("\ | |
140 | %s: line %d: list delimiter not followed by domain"), | |
141 | fname, line_num) < 0) | |
142 | return 0; | |
143 | ||
144 | __fxprintf (NULL, "%s", buf); | |
145 | ||
146 | free (buf); | |
147 | return 0; | |
148 | } | |
149 | default: | |
150 | break; | |
151 | } | |
152 | } | |
153 | while (*args && *args != '#'); | |
154 | return args; | |
155 | } | |
156 | ||
157 | ||
158 | static const char * | |
159 | arg_bool (const char *fname, int line_num, const char *args, unsigned flag) | |
160 | { | |
161 | if (__strncasecmp (args, "on", 2) == 0) | |
162 | { | |
163 | args += 2; | |
164 | _res_hconf.flags |= flag; | |
165 | } | |
166 | else if (__strncasecmp (args, "off", 3) == 0) | |
167 | { | |
168 | args += 3; | |
169 | _res_hconf.flags &= ~flag; | |
170 | } | |
171 | else | |
172 | { | |
173 | char *buf; | |
174 | ||
175 | if (__asprintf (&buf, | |
176 | _("%s: line %d: expected `on' or `off', found `%s'\n"), | |
177 | fname, line_num, args) < 0) | |
178 | return 0; | |
179 | ||
180 | __fxprintf (NULL, "%s", buf); | |
181 | ||
182 | free (buf); | |
183 | return 0; | |
184 | } | |
185 | return args; | |
186 | } | |
187 | ||
188 | ||
189 | static void | |
190 | parse_line (const char *fname, int line_num, const char *str) | |
191 | { | |
192 | const char *start; | |
193 | const struct cmd *c = 0; | |
194 | size_t len; | |
195 | size_t i; | |
196 | ||
197 | str = skip_ws (str); | |
198 | ||
199 | /* skip line comment and empty lines: */ | |
200 | if (*str == '\0' || *str == '#') return; | |
201 | ||
202 | start = str; | |
203 | str = skip_string (str); | |
204 | len = str - start; | |
205 | ||
206 | for (i = 0; i < sizeof (cmd) / sizeof (cmd[0]); ++i) | |
207 | { | |
208 | if (__strncasecmp (start, cmd[i].name, len) == 0 | |
209 | && strlen (cmd[i].name) == len) | |
210 | { | |
211 | c = &cmd[i]; | |
212 | break; | |
213 | } | |
214 | } | |
215 | if (c == NULL) | |
216 | { | |
217 | char *buf; | |
218 | ||
219 | if (__asprintf (&buf, _("%s: line %d: bad command `%s'\n"), | |
220 | fname, line_num, start) < 0) | |
221 | return; | |
222 | ||
223 | __fxprintf (NULL, "%s", buf); | |
224 | ||
225 | free (buf); | |
226 | return; | |
227 | } | |
228 | ||
229 | /* process args: */ | |
230 | str = skip_ws (str); | |
231 | ||
232 | if (c->cb == CB_arg_trimdomain_list) | |
233 | str = arg_trimdomain_list (fname, line_num, str); | |
234 | else if (c->cb == CB_arg_bool) | |
235 | str = arg_bool (fname, line_num, str, c->arg); | |
236 | else | |
237 | /* Ignore the line. */ | |
238 | return; | |
239 | ||
240 | if (!str) | |
241 | return; | |
242 | ||
243 | /* rest of line must contain white space or comment only: */ | |
244 | while (*str) | |
245 | { | |
246 | if (!isspace (*str)) { | |
247 | if (*str != '#') | |
248 | { | |
249 | char *buf; | |
250 | ||
251 | if (__asprintf (&buf, | |
252 | _("%s: line %d: ignoring trailing garbage `%s'\n"), | |
253 | fname, line_num, str) < 0) | |
254 | break; | |
255 | ||
256 | __fxprintf (NULL, "%s", buf); | |
257 | ||
258 | free (buf); | |
259 | } | |
260 | break; | |
261 | } | |
262 | ++str; | |
263 | } | |
264 | } | |
265 | ||
266 | ||
267 | static void | |
268 | do_init (void) | |
269 | { | |
270 | const char *hconf_name; | |
271 | int line_num = 0; | |
272 | char buf[256], *envval; | |
273 | FILE *fp; | |
274 | ||
275 | memset (&_res_hconf, '\0', sizeof (_res_hconf)); | |
276 | ||
277 | hconf_name = getenv (ENV_HOSTCONF); | |
278 | if (hconf_name == NULL) | |
279 | hconf_name = _PATH_HOSTCONF; | |
280 | ||
281 | fp = fopen (hconf_name, "rce"); | |
282 | if (fp) | |
283 | { | |
284 | /* No threads using this stream. */ | |
285 | __fsetlocking (fp, FSETLOCKING_BYCALLER); | |
286 | ||
287 | while (fgets_unlocked (buf, sizeof (buf), fp)) | |
288 | { | |
289 | ++line_num; | |
290 | *__strchrnul (buf, '\n') = '\0'; | |
291 | parse_line (hconf_name, line_num, buf); | |
292 | } | |
293 | fclose (fp); | |
294 | } | |
295 | ||
296 | envval = getenv (ENV_MULTI); | |
297 | if (envval) | |
298 | arg_bool (ENV_MULTI, 1, envval, HCONF_FLAG_MULTI); | |
299 | ||
300 | envval = getenv (ENV_REORDER); | |
301 | if (envval) | |
302 | arg_bool (ENV_REORDER, 1, envval, HCONF_FLAG_REORDER); | |
303 | ||
304 | envval = getenv (ENV_TRIM_ADD); | |
305 | if (envval) | |
306 | arg_trimdomain_list (ENV_TRIM_ADD, 1, envval); | |
307 | ||
308 | envval = getenv (ENV_TRIM_OVERR); | |
309 | if (envval) | |
310 | { | |
311 | _res_hconf.num_trimdomains = 0; | |
312 | arg_trimdomain_list (ENV_TRIM_OVERR, 1, envval); | |
313 | } | |
314 | ||
315 | /* See comments on the declaration of _res_hconf. */ | |
316 | atomic_store_release (&_res_hconf.initialized, 1); | |
317 | } | |
318 | ||
319 | ||
320 | /* Initialize hconf datastructure by reading host.conf file and | |
321 | environment variables. */ | |
322 | void | |
323 | _res_hconf_init (void) | |
324 | { | |
325 | __libc_once_define (static, once); | |
326 | ||
327 | __libc_once (once, do_init); | |
328 | } | |
329 | ||
330 | ||
331 | #if IS_IN (libc) | |
332 | # if defined SIOCGIFCONF && defined SIOCGIFNETMASK | |
333 | /* List of known interfaces. */ | |
334 | libc_freeres_ptr ( | |
335 | static struct netaddr | |
336 | { | |
337 | int addrtype; | |
338 | union | |
339 | { | |
340 | struct | |
341 | { | |
342 | uint32_t addr; | |
343 | uint32_t mask; | |
344 | } ipv4; | |
345 | } u; | |
346 | } *ifaddrs); | |
347 | # endif | |
348 | ||
349 | /* Reorder addresses returned in a hostent such that the first address | |
350 | is an address on the local subnet, if there is such an address. | |
351 | Otherwise, nothing is changed. | |
352 | ||
353 | Note that this function currently only handles IPv4 addresses. */ | |
354 | ||
355 | void | |
356 | _res_hconf_reorder_addrs (struct hostent *hp) | |
357 | { | |
358 | #if defined SIOCGIFCONF && defined SIOCGIFNETMASK | |
359 | int i, j; | |
360 | /* Number of interfaces. Also serves as a flag for the | |
361 | double-checked locking idiom. */ | |
362 | static int num_ifs = -1; | |
363 | /* Local copy of num_ifs, for non-atomic access. */ | |
364 | int num_ifs_local; | |
365 | /* We need to protect the dynamic buffer handling. The lock is only | |
366 | acquired during initialization. Afterwards, a positive num_ifs | |
367 | value indicates completed initialization. */ | |
368 | __libc_lock_define_initialized (static, lock); | |
369 | ||
370 | /* Only reorder if we're supposed to. */ | |
371 | if ((_res_hconf.flags & HCONF_FLAG_REORDER) == 0) | |
372 | return; | |
373 | ||
374 | /* Can't deal with anything but IPv4 for now... */ | |
375 | if (hp->h_addrtype != AF_INET) | |
376 | return; | |
377 | ||
378 | /* This load synchronizes with the release MO store in the | |
379 | initialization block below. */ | |
380 | num_ifs_local = atomic_load_acquire (&num_ifs); | |
381 | if (num_ifs_local <= 0) | |
382 | { | |
383 | struct ifreq *ifr, *cur_ifr; | |
384 | int sd, num, i; | |
385 | /* Save errno. */ | |
386 | int save = errno; | |
387 | ||
388 | /* Initialize interface table. */ | |
389 | ||
390 | /* The SIOCGIFNETMASK ioctl will only work on an AF_INET socket. */ | |
391 | sd = __socket (AF_INET, SOCK_DGRAM | SOCK_CLOEXEC, 0); | |
392 | if (sd < 0) | |
393 | return; | |
394 | ||
395 | /* Get lock. */ | |
396 | __libc_lock_lock (lock); | |
397 | ||
398 | /* Recheck, somebody else might have done the work by now. No | |
399 | ordering is required for the load because we have the lock, | |
400 | and num_ifs is only updated under the lock. Also see (3) in | |
401 | the analysis below. */ | |
402 | num_ifs_local = atomic_load_relaxed (&num_ifs); | |
403 | if (num_ifs_local <= 0) | |
404 | { | |
405 | /* This is the only block which writes to num_ifs. It can | |
406 | be executed several times (sequentially) if | |
407 | initialization does not yield any interfaces, and num_ifs | |
408 | remains zero. However, once we stored a positive value | |
409 | in num_ifs below, this block cannot be entered again due | |
410 | to the condition above. */ | |
411 | int new_num_ifs = 0; | |
412 | ||
413 | /* Get a list of interfaces. */ | |
414 | __ifreq (&ifr, &num, sd); | |
415 | if (!ifr) | |
416 | goto cleanup; | |
417 | ||
418 | ifaddrs = malloc (num * sizeof (ifaddrs[0])); | |
419 | if (!ifaddrs) | |
420 | goto cleanup1; | |
421 | ||
422 | /* Copy usable interfaces in ifaddrs structure. */ | |
423 | for (cur_ifr = ifr, i = 0; i < num; | |
424 | cur_ifr = __if_nextreq (cur_ifr), ++i) | |
425 | { | |
426 | union | |
427 | { | |
428 | struct sockaddr sa; | |
429 | struct sockaddr_in sin; | |
430 | } ss; | |
431 | ||
432 | if (cur_ifr->ifr_addr.sa_family != AF_INET) | |
433 | continue; | |
434 | ||
435 | ifaddrs[new_num_ifs].addrtype = AF_INET; | |
436 | ss.sa = cur_ifr->ifr_addr; | |
437 | ifaddrs[new_num_ifs].u.ipv4.addr = ss.sin.sin_addr.s_addr; | |
438 | ||
439 | if (__ioctl (sd, SIOCGIFNETMASK, cur_ifr) < 0) | |
440 | continue; | |
441 | ||
442 | ss.sa = cur_ifr->ifr_netmask; | |
443 | ifaddrs[new_num_ifs].u.ipv4.mask = ss.sin.sin_addr.s_addr; | |
444 | ||
445 | /* Now we're committed to this entry. */ | |
446 | ++new_num_ifs; | |
447 | } | |
448 | /* Just keep enough memory to hold all the interfaces we want. */ | |
449 | ifaddrs = realloc (ifaddrs, new_num_ifs * sizeof (ifaddrs[0])); | |
450 | assert (ifaddrs != NULL); | |
451 | ||
452 | cleanup1: | |
453 | __if_freereq (ifr, num); | |
454 | ||
455 | cleanup: | |
456 | /* Release lock, preserve error value, and close socket. */ | |
457 | errno = save; | |
458 | ||
459 | /* Advertise successful initialization if new_num_ifs is | |
460 | positive (and no updates to ifaddrs are permitted after | |
461 | that). Otherwise, num_ifs remains unchanged, at zero. | |
462 | This store synchronizes with the initial acquire MO | |
463 | load. */ | |
464 | atomic_store_release (&num_ifs, new_num_ifs); | |
465 | /* Keep the local copy current, to save another load. */ | |
466 | num_ifs_local = new_num_ifs; | |
467 | } | |
468 | ||
469 | __libc_lock_unlock (lock); | |
470 | ||
471 | __close (sd); | |
472 | } | |
473 | ||
474 | /* num_ifs_local cannot be negative because the if statement above | |
475 | covered this case. It can still be zero if we just performed | |
476 | initialization, but could not find any interfaces. */ | |
477 | if (num_ifs_local == 0) | |
478 | return; | |
479 | ||
480 | /* The code below accesses ifaddrs, so we need to ensure that the | |
481 | initialization happens-before this point. | |
482 | ||
483 | The actual initialization is sequenced-before the release store | |
484 | to num_ifs, and sequenced-before the end of the critical section. | |
485 | ||
486 | This means there are three possible executions: | |
487 | ||
488 | (1) The thread that initialized the data also uses it, so | |
489 | sequenced-before is sufficient to ensure happens-before. | |
490 | ||
491 | (2) The release MO store of num_ifs synchronizes-with the acquire | |
492 | MO load, and the acquire MO load is sequenced before the use | |
493 | of the initialized data below. | |
494 | ||
495 | (3) We enter the critical section, and the relaxed MO load of | |
496 | num_ifs yields a positive value. The write to ifaddrs is | |
497 | sequenced-before leaving the critical section. Leaving the | |
498 | critical section happens-before we entered the critical | |
499 | section ourselves, which means that the write to ifaddrs | |
500 | happens-before this point. | |
501 | ||
502 | Consequently, all potential writes to ifaddrs (and the data it | |
503 | points to) happens-before this point. */ | |
504 | ||
505 | /* Find an address for which we have a direct connection. */ | |
506 | for (i = 0; hp->h_addr_list[i]; ++i) | |
507 | { | |
508 | struct in_addr *haddr = (struct in_addr *) hp->h_addr_list[i]; | |
509 | ||
510 | for (j = 0; j < num_ifs_local; ++j) | |
511 | { | |
512 | uint32_t if_addr = ifaddrs[j].u.ipv4.addr; | |
513 | uint32_t if_netmask = ifaddrs[j].u.ipv4.mask; | |
514 | ||
515 | if (((haddr->s_addr ^ if_addr) & if_netmask) == 0) | |
516 | { | |
517 | void *tmp; | |
518 | ||
519 | tmp = hp->h_addr_list[i]; | |
520 | hp->h_addr_list[i] = hp->h_addr_list[0]; | |
521 | hp->h_addr_list[0] = tmp; | |
522 | return; | |
523 | } | |
524 | } | |
525 | } | |
526 | #endif /* defined(SIOCGIFCONF) && ... */ | |
527 | } | |
528 | ||
529 | ||
530 | /* If HOSTNAME has a postfix matching any of the trimdomains, trim away | |
531 | that postfix. Notice that HOSTNAME is modified inplace. Also, the | |
532 | original code applied all trimdomains in order, meaning that the | |
533 | same domainname could be trimmed multiple times. I believe this | |
534 | was unintentional. */ | |
535 | void | |
536 | _res_hconf_trim_domain (char *hostname) | |
537 | { | |
538 | size_t hostname_len, trim_len; | |
539 | int i; | |
540 | ||
541 | hostname_len = strlen (hostname); | |
542 | ||
543 | for (i = 0; i < _res_hconf.num_trimdomains; ++i) | |
544 | { | |
545 | const char *trim = _res_hconf.trimdomain[i]; | |
546 | ||
547 | trim_len = strlen (trim); | |
548 | if (hostname_len > trim_len | |
549 | && __strcasecmp (&hostname[hostname_len - trim_len], trim) == 0) | |
550 | { | |
551 | hostname[hostname_len - trim_len] = '\0'; | |
552 | break; | |
553 | } | |
554 | } | |
555 | } | |
556 | ||
557 | ||
558 | /* Trim all hostnames/aliases in HP according to the trimdomain list. | |
559 | Notice that HP is modified inplace! */ | |
560 | void | |
561 | _res_hconf_trim_domains (struct hostent *hp) | |
562 | { | |
563 | int i; | |
564 | ||
565 | if (_res_hconf.num_trimdomains == 0) | |
566 | return; | |
567 | ||
568 | _res_hconf_trim_domain (hp->h_name); | |
569 | for (i = 0; hp->h_aliases[i]; ++i) | |
570 | _res_hconf_trim_domain (hp->h_aliases[i]); | |
571 | } | |
572 | #endif |