1 /* cache.c - keep a cache of passphrases
2 * Copyright (C) 2002, 2010 Free Software Foundation, Inc.
4 * This file is part of GnuPG.
6 * GnuPG is free software; you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License as published by
8 * the Free Software Foundation; either version 3 of the License, or
9 * (at your option) any later version.
11 * GnuPG is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 * GNU General Public License for more details.
16 * You should have received a copy of the GNU General Public License
17 * along with this program; if not, see <http://www.gnu.org/licenses/>.
31 /* The size of the encryption key in bytes. */
32 #define ENCRYPTION_KEYSIZE (128/8)
34 /* A mutex used to protect the encryption. This is required because
35 we use one context to do all encryption and decryption. */
36 static npth_mutex_t encryption_lock;
37 /* The encryption context. This is the only place where the
38 encryption key for all cached entries is available. It would be nice
39 to keep this (or just the key) in some hardware device, for example
40 a TPM. Libgcrypt could be extended to provide such a service.
41 With the current scheme it is easy to retrieve the cached entries
42 if access to Libgcrypt's memory is available. The encryption
43 merely avoids grepping for clear texts in the memory. Nevertheless
44 the encryption provides the necessary infrastructure to make it
46 static gcry_cipher_hd_t encryption_handle;
49 struct secret_data_s {
50 int totallen; /* This includes the padding and space for AESWRAP. */
51 char data[1]; /* A string. */
54 typedef struct cache_item_s *ITEM;
59 int ttl; /* max. lifetime given in seconds, -1 one means infinite */
60 struct secret_data_s *pw;
61 cache_mode_t cache_mode;
65 /* The cache himself. */
68 /* NULL or the last cache key stored by agent_store_cache_hit. */
69 static char *last_stored_cache_key;
72 /* This function must be called once to initialize this module. It
73 has to be done before a second thread is spawned. */
75 initialize_module_cache (void)
79 err = npth_mutex_init (&encryption_lock, NULL);
82 log_fatal ("error initializing cache module: %s\n", strerror (err));
87 deinitialize_module_cache (void)
89 gcry_cipher_close (encryption_handle);
90 encryption_handle = NULL;
94 /* We do the encryption init on the fly. We can't do it in the module
95 init code because that is run before we listen for connections and
96 in case we are started on demand by gpg etc. it will only wait for
97 a few seconds to decide whether the agent may now accept
98 connections. Thus we should get into listen state as soon as
101 init_encryption (void)
107 if (encryption_handle)
108 return 0; /* Shortcut - Already initialized. */
110 res = npth_mutex_lock (&encryption_lock);
112 log_fatal ("failed to acquire cache encryption mutex: %s\n", strerror (res));
114 err = gcry_cipher_open (&encryption_handle, GCRY_CIPHER_AES128,
115 GCRY_CIPHER_MODE_AESWRAP, GCRY_CIPHER_SECURE);
118 key = gcry_random_bytes (ENCRYPTION_KEYSIZE, GCRY_STRONG_RANDOM);
120 err = gpg_error_from_syserror ();
123 err = gcry_cipher_setkey (encryption_handle, key, ENCRYPTION_KEYSIZE);
128 gcry_cipher_close (encryption_handle);
129 encryption_handle = NULL;
133 log_error ("error initializing cache encryption context: %s\n",
136 res = npth_mutex_unlock (&encryption_lock);
138 log_fatal ("failed to release cache encryption mutex: %s\n", strerror (res));
140 return err? gpg_error (GPG_ERR_NOT_INITIALIZED) : 0;
146 release_data (struct secret_data_s *data)
152 new_data (const char *string, struct secret_data_s **r_data)
155 struct secret_data_s *d, *d_enc;
162 err = init_encryption ();
166 length = strlen (string) + 1;
168 /* We pad the data to 32 bytes so that it get more complicated
169 finding something out by watching allocation patterns. This is
170 usually not possible but we better assume nothing about our secure
171 storage provider. To support the AESWRAP mode we need to add 8
172 extra bytes as well. */
173 total = (length + 8) + 32 - ((length+8) % 32);
175 d = xtrymalloc_secure (sizeof *d + total - 1);
177 return gpg_error_from_syserror ();
178 memcpy (d->data, string, length);
180 d_enc = xtrymalloc (sizeof *d_enc + total - 1);
183 err = gpg_error_from_syserror ();
188 d_enc->totallen = total;
189 res = npth_mutex_lock (&encryption_lock);
191 log_fatal ("failed to acquire cache encryption mutex: %s\n",
194 err = gcry_cipher_encrypt (encryption_handle, d_enc->data, total,
197 res = npth_mutex_unlock (&encryption_lock);
199 log_fatal ("failed to release cache encryption mutex: %s\n", strerror (res));
211 /* Check whether there are items to expire. */
216 time_t current = gnupg_get_time ();
218 /* First expire the actual data */
219 for (r=thecache; r; r = r->next)
221 if (r->pw && r->ttl >= 0 && r->accessed + r->ttl < current)
224 log_debug (" expired '%s' (%ds after last access)\n",
226 release_data (r->pw);
228 r->accessed = current;
232 /* Second, make sure that we also remove them based on the created stamp so
233 that the user has to enter it from time to time. */
234 for (r=thecache; r; r = r->next)
236 unsigned long maxttl;
238 switch (r->cache_mode)
240 case CACHE_MODE_SSH: maxttl = opt.max_cache_ttl_ssh; break;
241 default: maxttl = opt.max_cache_ttl; break;
243 if (r->pw && r->created + maxttl < current)
246 log_debug (" expired '%s' (%lus after creation)\n",
247 r->key, opt.max_cache_ttl);
248 release_data (r->pw);
250 r->accessed = current;
254 /* Third, make sure that we don't have too many items in the list.
255 Expire old and unused entries after 30 minutes */
256 for (rprev=NULL, r=thecache; r; )
258 if (!r->pw && r->ttl >= 0 && r->accessed + 60*30 < current)
262 log_debug (" removed '%s' (mode %d) (slot not used for 30m)\n",
263 r->key, r->cache_mode);
281 agent_flush_cache (void)
286 log_debug ("agent_flush_cache\n");
288 for (r=thecache; r; r = r->next)
293 log_debug (" flushing '%s'\n", r->key);
294 release_data (r->pw);
303 /* Store the string DATA in the cache under KEY and mark it with a
304 maximum lifetime of TTL seconds. If there is already data under
305 this key, it will be replaced. Using a DATA of NULL deletes the
306 entry. A TTL of 0 is replaced by the default TTL and a TTL of -1
307 set infinite timeout. CACHE_MODE is stored with the cache entry
308 and used to select different timeouts. */
310 agent_put_cache (const char *key, cache_mode_t cache_mode,
311 const char *data, int ttl)
317 log_debug ("agent_put_cache '%s' (mode %d) requested ttl=%d\n",
318 key, cache_mode, ttl);
325 case CACHE_MODE_SSH: ttl = opt.def_cache_ttl_ssh; break;
326 default: ttl = opt.def_cache_ttl; break;
329 if ((!ttl && data) || cache_mode == CACHE_MODE_IGNORE)
332 for (r=thecache; r; r = r->next)
334 if (((cache_mode != CACHE_MODE_USER
335 && cache_mode != CACHE_MODE_NONCE)
336 || r->cache_mode == cache_mode)
337 && !strcmp (r->key, key))
340 if (r) /* Replace. */
344 release_data (r->pw);
349 r->created = r->accessed = gnupg_get_time ();
351 r->cache_mode = cache_mode;
352 err = new_data (data, &r->pw);
354 log_error ("error replacing cache item: %s\n", gpg_strerror (err));
357 else if (data) /* Insert. */
359 r = xtrycalloc (1, sizeof *r + strlen (key));
361 err = gpg_error_from_syserror ();
364 strcpy (r->key, key);
365 r->created = r->accessed = gnupg_get_time ();
367 r->cache_mode = cache_mode;
368 err = new_data (data, &r->pw);
378 log_error ("error inserting cache item: %s\n", gpg_strerror (err));
384 /* Try to find an item in the cache. Note that we currently don't
385 make use of CACHE_MODE except for CACHE_MODE_NONCE and
388 agent_get_cache (const char *key, cache_mode_t cache_mode)
396 if (cache_mode == CACHE_MODE_IGNORE)
401 key = last_stored_cache_key;
409 log_debug ("agent_get_cache '%s' (mode %d)%s ...\n",
411 last_stored? " (stored cache key)":"");
414 for (r=thecache; r; r = r->next)
417 && ((cache_mode != CACHE_MODE_USER
418 && cache_mode != CACHE_MODE_NONCE)
419 || r->cache_mode == cache_mode)
420 && !strcmp (r->key, key))
422 /* Note: To avoid races KEY may not be accessed anymore below. */
423 r->accessed = gnupg_get_time ();
425 log_debug ("... hit\n");
426 if (r->pw->totallen < 32)
427 err = gpg_error (GPG_ERR_INV_LENGTH);
428 else if ((err = init_encryption ()))
430 else if (!(value = xtrymalloc_secure (r->pw->totallen - 8)))
431 err = gpg_error_from_syserror ();
434 res = npth_mutex_lock (&encryption_lock);
436 log_fatal ("failed to acquire cache encryption mutex: %s\n",
438 err = gcry_cipher_decrypt (encryption_handle,
439 value, r->pw->totallen - 8,
440 r->pw->data, r->pw->totallen);
441 res = npth_mutex_unlock (&encryption_lock);
443 log_fatal ("failed to release cache encryption mutex: %s\n",
450 log_error ("retrieving cache entry '%s' failed: %s\n",
451 key, gpg_strerror (err));
457 log_debug ("... miss\n");
463 /* Store the key for the last successful cache hit. That value is
464 used by agent_get_cache if the requested KEY is given as NULL.
465 NULL may be used to remove that key. */
467 agent_store_cache_hit (const char *key)
469 xfree (last_stored_cache_key);
470 last_stored_cache_key = key? xtrystrdup (key) : NULL;