1 /* Cache handling for host lookup.
2 Copyright (C) 1998-2023 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4
5 This program is free software; you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published
7 by the Free Software Foundation; version 2 of the License, or
8 (at your option) any later version.
9
10 This program 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
13 GNU General Public License for more details.
14
15 You should have received a copy of the GNU General Public License
16 along with this program; if not, see <https://www.gnu.org/licenses/>. */
17
18 #include <alloca.h>
19 #include <assert.h>
20 #include <errno.h>
21 #include <error.h>
22 #include <libintl.h>
23 #include <netdb.h>
24 #include <stdbool.h>
25 #include <stddef.h>
26 #include <stdio.h>
27 #include <stdlib.h>
28 #include <string.h>
29 #include <time.h>
30 #include <unistd.h>
31 #include <stdint.h>
32 #include <arpa/inet.h>
33 #include <arpa/nameser.h>
34 #include <sys/mman.h>
35 #include <stackinfo.h>
36 #include <scratch_buffer.h>
37
38 #include "nscd.h"
39 #include "dbg_log.h"
40
41
42 /* This is the standard reply in case the service is disabled. */
43 static const hst_response_header disabled =
44 {
45 .version = NSCD_VERSION,
46 .found = -1,
47 .h_name_len = 0,
48 .h_aliases_cnt = 0,
49 .h_addrtype = -1,
50 .h_length = -1,
51 .h_addr_list_cnt = 0,
52 .error = NETDB_INTERNAL
53 };
54
55 /* This is the struct describing how to write this record. */
56 const struct iovec hst_iov_disabled =
57 {
58 .iov_base = (void *) &disabled,
59 .iov_len = sizeof (disabled)
60 };
61
62
63 /* This is the standard reply in case we haven't found the dataset. */
64 static const hst_response_header notfound =
65 {
66 .version = NSCD_VERSION,
67 .found = 0,
68 .h_name_len = 0,
69 .h_aliases_cnt = 0,
70 .h_addrtype = -1,
71 .h_length = -1,
72 .h_addr_list_cnt = 0,
73 .error = HOST_NOT_FOUND
74 };
75
76
77 /* This is the standard reply in case there are temporary problems. */
78 static const hst_response_header tryagain =
79 {
80 .version = NSCD_VERSION,
81 .found = 0,
82 .h_name_len = 0,
83 .h_aliases_cnt = 0,
84 .h_addrtype = -1,
85 .h_length = -1,
86 .h_addr_list_cnt = 0,
87 .error = TRY_AGAIN
88 };
89
90
91 static time_t
92 cache_addhst (struct database_dyn *db, int fd, request_header *req,
93 const void *key, struct hostent *hst, uid_t owner,
94 struct hashentry *const he, struct datahead *dh, int errval,
95 int32_t ttl)
96 {
97 bool all_written = true;
98 time_t t = time (NULL);
99
100 /* We allocate all data in one memory block: the iov vector,
101 the response header and the dataset itself. */
102 struct dataset
103 {
104 struct datahead head;
105 hst_response_header resp;
106 char strdata[0];
107 } *dataset;
108
109 assert (offsetof (struct dataset, resp) == offsetof (struct datahead, data));
110
111 time_t timeout = MAX_TIMEOUT_VALUE;
112 if (hst == NULL)
113 {
114 if (he != NULL && errval == EAGAIN)
115 {
116 /* If we have an old record available but cannot find one
117 now because the service is not available we keep the old
118 record and make sure it does not get removed. */
119 if (reload_count != UINT_MAX)
120 /* Do not reset the value if we never not reload the record. */
121 dh->nreloads = reload_count - 1;
122
123 /* Reload with the same time-to-live value. */
124 timeout = dh->timeout = t + dh->ttl;
125 }
126 else
127 {
128 /* We have no data. This means we send the standard reply for this
129 case. Possibly this is only temporary. */
130 ssize_t total = sizeof (notfound);
131 assert (sizeof (notfound) == sizeof (tryagain));
132
133 const hst_response_header *resp = (errval == EAGAIN
134 ? &tryagain : ¬found);
135
136 if (fd != -1
137 && TEMP_FAILURE_RETRY (send (fd, resp, total,
138 MSG_NOSIGNAL)) != total)
139 all_written = false;
140
141 /* If we have a transient error or cannot permanently store
142 the result, so be it. */
143 if (errval == EAGAIN || __builtin_expect (db->negtimeout == 0, 0))
144 {
145 /* Mark the old entry as obsolete. */
146 if (dh != NULL)
147 dh->usable = false;
148 }
149 else if ((dataset = mempool_alloc (db, (sizeof (struct dataset)
150 + req->key_len), 1)) != NULL)
151 {
152 timeout = datahead_init_neg (&dataset->head,
153 (sizeof (struct dataset)
154 + req->key_len), total,
155 (ttl == INT32_MAX
156 ? db->negtimeout : ttl));
157
158 /* This is the reply. */
159 memcpy (&dataset->resp, resp, total);
160
161 /* Copy the key data. */
162 memcpy (dataset->strdata, key, req->key_len);
163
164 /* If necessary, we also propagate the data to disk. */
165 if (db->persistent)
166 {
167 // XXX async OK?
168 uintptr_t pval = (uintptr_t) dataset & ~pagesize_m1;
169 msync ((void *) pval,
170 ((uintptr_t) dataset & pagesize_m1)
171 + sizeof (struct dataset) + req->key_len, MS_ASYNC);
172 }
173
174 (void) cache_add (req->type, &dataset->strdata, req->key_len,
175 &dataset->head, true, db, owner, he == NULL);
176
177 pthread_rwlock_unlock (&db->lock);
178
179 /* Mark the old entry as obsolete. */
180 if (dh != NULL)
181 dh->usable = false;
182 }
183 }
184 }
185 else
186 {
187 /* Determine the I/O structure. */
188 size_t h_name_len = strlen (hst->h_name) + 1;
189 size_t h_aliases_cnt;
190 uint32_t *h_aliases_len;
191 size_t h_addr_list_cnt;
192 char *addresses;
193 char *aliases;
194 char *key_copy = NULL;
195 char *cp;
196 size_t cnt;
197 ssize_t total;
198
199 /* Determine the number of aliases. */
200 h_aliases_cnt = 0;
201 for (cnt = 0; hst->h_aliases[cnt] != NULL; ++cnt)
202 ++h_aliases_cnt;
203 /* Determine the length of all aliases. */
204 h_aliases_len = (uint32_t *) alloca (h_aliases_cnt * sizeof (uint32_t));
205 total = 0;
206 for (cnt = 0; cnt < h_aliases_cnt; ++cnt)
207 {
208 h_aliases_len[cnt] = strlen (hst->h_aliases[cnt]) + 1;
209 total += h_aliases_len[cnt];
210 }
211
212 /* Determine the number of addresses. */
213 h_addr_list_cnt = 0;
214 while (hst->h_addr_list[h_addr_list_cnt] != NULL)
215 ++h_addr_list_cnt;
216
217 if (h_addr_list_cnt == 0)
218 /* Invalid entry. */
219 return MAX_TIMEOUT_VALUE;
220
221 total += (sizeof (struct dataset)
222 + h_name_len
223 + h_aliases_cnt * sizeof (uint32_t)
224 + h_addr_list_cnt * hst->h_length);
225
226 /* If we refill the cache, first assume the reconrd did not
227 change. Allocate memory on the cache since it is likely
228 discarded anyway. If it turns out to be necessary to have a
229 new record we can still allocate real memory. */
230 bool alloca_used = false;
231 dataset = NULL;
232
233 /* If the record contains more than one IP address (used for
234 load balancing etc) don't cache the entry. This is something
235 the current cache handling cannot handle and it is more than
236 questionable whether it is worthwhile complicating the cache
237 handling just for handling such a special case. */
238 if (he == NULL && h_addr_list_cnt == 1)
239 dataset = (struct dataset *) mempool_alloc (db, total + req->key_len,
240 1);
241
242 if (dataset == NULL)
243 {
244 /* We cannot permanently add the result in the moment. But
245 we can provide the result as is. Store the data in some
246 temporary memory. */
247 dataset = (struct dataset *) alloca (total + req->key_len);
248
249 /* We cannot add this record to the permanent database. */
250 alloca_used = true;
251 }
252
253 timeout = datahead_init_pos (&dataset->head, total + req->key_len,
254 total - offsetof (struct dataset, resp),
255 he == NULL ? 0 : dh->nreloads + 1,
256 ttl == INT32_MAX ? db->postimeout : ttl);
257
258 dataset->resp.version = NSCD_VERSION;
259 dataset->resp.found = 1;
260 dataset->resp.h_name_len = h_name_len;
261 dataset->resp.h_aliases_cnt = h_aliases_cnt;
262 dataset->resp.h_addrtype = hst->h_addrtype;
263 dataset->resp.h_length = hst->h_length;
264 dataset->resp.h_addr_list_cnt = h_addr_list_cnt;
265 dataset->resp.error = NETDB_SUCCESS;
266
267 /* Make sure there is no gap. */
268 assert ((char *) (&dataset->resp.error + 1) == dataset->strdata);
269
270 cp = dataset->strdata;
271
272 cp = mempcpy (cp, hst->h_name, h_name_len);
273 cp = mempcpy (cp, h_aliases_len, h_aliases_cnt * sizeof (uint32_t));
274
275 /* The normal addresses first. */
276 addresses = cp;
277 for (cnt = 0; cnt < h_addr_list_cnt; ++cnt)
278 cp = mempcpy (cp, hst->h_addr_list[cnt], hst->h_length);
279
280 /* Then the aliases. */
281 aliases = cp;
282 for (cnt = 0; cnt < h_aliases_cnt; ++cnt)
283 cp = mempcpy (cp, hst->h_aliases[cnt], h_aliases_len[cnt]);
284
285 assert (cp
286 == dataset->strdata + total - offsetof (struct dataset,
287 strdata));
288
289 /* If we are adding a GETHOSTBYNAME{,v6} entry we must be prepared
290 that the answer we get from the NSS does not contain the key
291 itself. This is the case if the resolver is used and the name
292 is extended by the domainnames from /etc/resolv.conf. Therefore
293 we explicitly add the name here. */
294 key_copy = memcpy (cp, key, req->key_len);
295
296 assert ((char *) &dataset->resp + dataset->head.recsize == cp);
297
298 /* Now we can determine whether on refill we have to create a new
299 record or not. */
300 if (he != NULL)
301 {
302 assert (fd == -1);
303
304 if (total + req->key_len == dh->allocsize
305 && total - offsetof (struct dataset, resp) == dh->recsize
306 && memcmp (&dataset->resp, dh->data,
307 dh->allocsize - offsetof (struct dataset, resp)) == 0)
308 {
309 /* The data has not changed. We will just bump the
310 timeout value. Note that the new record has been
311 allocated on the stack and need not be freed. */
312 assert (h_addr_list_cnt == 1);
313 dh->ttl = dataset->head.ttl;
314 dh->timeout = dataset->head.timeout;
315 ++dh->nreloads;
316 }
317 else
318 {
319 if (h_addr_list_cnt == 1)
320 {
321 /* We have to create a new record. Just allocate
322 appropriate memory and copy it. */
323 struct dataset *newp
324 = (struct dataset *) mempool_alloc (db,
325 total + req->key_len,
326 1);
327 if (newp != NULL)
328 {
329 /* Adjust pointers into the memory block. */
330 addresses = (char *) newp + (addresses
331 - (char *) dataset);
332 aliases = (char *) newp + (aliases - (char *) dataset);
333 assert (key_copy != NULL);
334 key_copy = (char *) newp + (key_copy - (char *) dataset);
335
336 dataset = memcpy (newp, dataset, total + req->key_len);
337 alloca_used = false;
338 }
339 }
340
341 /* Mark the old record as obsolete. */
342 dh->usable = false;
343 }
344 }
345 else
346 {
347 /* We write the dataset before inserting it to the database
348 since while inserting this thread might block and so would
349 unnecessarily keep the receiver waiting. */
350 assert (fd != -1);
351
352 if (writeall (fd, &dataset->resp, dataset->head.recsize)
353 != dataset->head.recsize)
354 all_written = false;
355 }
356
357 /* Add the record to the database. But only if it has not been
358 stored on the stack.
359
360 If the record contains more than one IP address (used for
361 load balancing etc) don't cache the entry. This is something
362 the current cache handling cannot handle and it is more than
363 questionable whether it is worthwhile complicating the cache
364 handling just for handling such a special case. */
365 if (! alloca_used)
366 {
367 /* If necessary, we also propagate the data to disk. */
368 if (db->persistent)
369 {
370 // XXX async OK?
371 uintptr_t pval = (uintptr_t) dataset & ~pagesize_m1;
372 msync ((void *) pval,
373 ((uintptr_t) dataset & pagesize_m1)
374 + total + req->key_len, MS_ASYNC);
375 }
376
377 /* NB: the following code is really complicated. It has
378 seemlingly duplicated code paths which do the same. The
379 problem is that we always must add the hash table entry
380 with the FIRST flag set first. Otherwise we get dangling
381 pointers in case memory allocation fails. */
382 assert (hst->h_addr_list[1] == NULL);
383
384 /* Avoid adding names if more than one address is available. See
385 above for more info. */
386 assert (req->type == GETHOSTBYNAME
387 || req->type == GETHOSTBYNAMEv6
388 || req->type == GETHOSTBYADDR
389 || req->type == GETHOSTBYADDRv6);
390
391 (void) cache_add (req->type, key_copy, req->key_len,
392 &dataset->head, true, db, owner, he == NULL);
393
394 pthread_rwlock_unlock (&db->lock);
395 }
396 }
397
398 if (__builtin_expect (!all_written, 0) && debug_level > 0)
399 {
400 char buf[256];
401 dbg_log (_("short write in %s: %s"), __FUNCTION__,
402 strerror_r (errno, buf, sizeof (buf)));
403 }
404
405 return timeout;
406 }
407
408
409 static int
410 lookup (int type, void *key, struct hostent *resultbufp, char *buffer,
411 size_t buflen, struct hostent **hst, int32_t *ttlp)
412 {
413 if (type == GETHOSTBYNAME)
414 return __gethostbyname3_r (key, AF_INET, resultbufp, buffer, buflen, hst,
415 &h_errno, ttlp, NULL);
416 if (type == GETHOSTBYNAMEv6)
417 return __gethostbyname3_r (key, AF_INET6, resultbufp, buffer, buflen, hst,
418 &h_errno, ttlp, NULL);
419 if (type == GETHOSTBYADDR)
420 return __gethostbyaddr2_r (key, NS_INADDRSZ, AF_INET, resultbufp, buffer,
421 buflen, hst, &h_errno, ttlp);
422 return __gethostbyaddr2_r (key, NS_IN6ADDRSZ, AF_INET6, resultbufp, buffer,
423 buflen, hst, &h_errno, ttlp);
424 }
425
426
427 static time_t
428 addhstbyX (struct database_dyn *db, int fd, request_header *req,
429 void *key, uid_t uid, struct hashentry *he, struct datahead *dh)
430 {
431 /* Search for the entry matching the key. Please note that we don't
432 look again in the table whether the dataset is now available. We
433 simply insert it. It does not matter if it is in there twice. The
434 pruning function only will look at the timestamp. */
435 struct hostent resultbuf;
436 struct hostent *hst;
437 int errval = 0;
438 int32_t ttl = INT32_MAX;
439
440 if (__glibc_unlikely (debug_level > 0))
441 {
442 const char *str;
443 char buf[INET6_ADDRSTRLEN + 1];
444 if (req->type == GETHOSTBYNAME || req->type == GETHOSTBYNAMEv6)
445 str = key;
446 else
447 str = inet_ntop (req->type == GETHOSTBYADDR ? AF_INET : AF_INET6,
448 key, buf, sizeof (buf));
449
450 if (he == NULL)
451 dbg_log (_("Haven't found \"%s\" in hosts cache!"), (char *) str);
452 else
453 dbg_log (_("Reloading \"%s\" in hosts cache!"), (char *) str);
454 }
455
456 struct scratch_buffer tmpbuf;
457 scratch_buffer_init (&tmpbuf);
458
459 while (lookup (req->type, key, &resultbuf,
460 tmpbuf.data, tmpbuf.length, &hst, &ttl) != 0
461 && h_errno == NETDB_INTERNAL
462 && (errval = errno) == ERANGE)
463 if (!scratch_buffer_grow (&tmpbuf))
464 {
465 /* We ran out of memory. We cannot do anything but sending a
466 negative response. In reality this should never
467 happen. */
468 hst = NULL;
469 /* We set the error to indicate this is (possibly) a temporary
470 error and that it does not mean the entry is not
471 available at all. */
472 h_errno = TRY_AGAIN;
473 errval = EAGAIN;
474 break;
475 }
476
477 time_t timeout = cache_addhst (db, fd, req, key, hst, uid, he, dh,
478 h_errno == TRY_AGAIN ? errval : 0, ttl);
479 scratch_buffer_free (&tmpbuf);
480 return timeout;
481 }
482
483
484 void
485 addhstbyname (struct database_dyn *db, int fd, request_header *req,
486 void *key, uid_t uid)
487 {
488 addhstbyX (db, fd, req, key, uid, NULL, NULL);
489 }
490
491
492 time_t
493 readdhstbyname (struct database_dyn *db, struct hashentry *he,
494 struct datahead *dh)
495 {
496 request_header req =
497 {
498 .type = GETHOSTBYNAME,
499 .key_len = he->len
500 };
501
502 return addhstbyX (db, -1, &req, db->data + he->key, he->owner, he, dh);
503 }
504
505
506 void
507 addhstbyaddr (struct database_dyn *db, int fd, request_header *req,
508 void *key, uid_t uid)
509 {
510 addhstbyX (db, fd, req, key, uid, NULL, NULL);
511 }
512
513
514 time_t
515 readdhstbyaddr (struct database_dyn *db, struct hashentry *he,
516 struct datahead *dh)
517 {
518 request_header req =
519 {
520 .type = GETHOSTBYADDR,
521 .key_len = he->len
522 };
523
524 return addhstbyX (db, -1, &req, db->data + he->key, he->owner, he, dh);
525 }
526
527
528 void
529 addhstbynamev6 (struct database_dyn *db, int fd, request_header *req,
530 void *key, uid_t uid)
531 {
532 addhstbyX (db, fd, req, key, uid, NULL, NULL);
533 }
534
535
536 time_t
537 readdhstbynamev6 (struct database_dyn *db, struct hashentry *he,
538 struct datahead *dh)
539 {
540 request_header req =
541 {
542 .type = GETHOSTBYNAMEv6,
543 .key_len = he->len
544 };
545
546 return addhstbyX (db, -1, &req, db->data + he->key, he->owner, he, dh);
547 }
548
549
550 void
551 addhstbyaddrv6 (struct database_dyn *db, int fd, request_header *req,
552 void *key, uid_t uid)
553 {
554 addhstbyX (db, fd, req, key, uid, NULL, NULL);
555 }
556
557
558 time_t
559 readdhstbyaddrv6 (struct database_dyn *db, struct hashentry *he,
560 struct datahead *dh)
561 {
562 request_header req =
563 {
564 .type = GETHOSTBYADDRv6,
565 .key_len = he->len
566 };
567
568 return addhstbyX (db, -1, &req, db->data + he->key, he->owner, he, dh);
569 }