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443 lines
12 KiB
C
443 lines
12 KiB
C
/* cache.c - keep a cache of passphrases
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* Copyright (C) 2002, 2010 Free Software Foundation, Inc.
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*
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* This file is part of GnuPG.
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*
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* GnuPG is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 3 of the License, or
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* (at your option) any later version.
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*
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* GnuPG is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, see <http://www.gnu.org/licenses/>.
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*/
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#include <config.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <time.h>
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#include <assert.h>
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#include <npth.h>
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#include "agent.h"
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/* The size of the encryption key in bytes. */
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#define ENCRYPTION_KEYSIZE (128/8)
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/* A mutex used to protect the encryption. This is required because
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we use one context to do all encryption and decryption. */
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static npth_mutex_t encryption_lock;
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/* The encryption context. This is the only place where the
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encryption key for all cached entries is available. It would be nice
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to keep this (or just the key) in some hardware device, for example
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a TPM. Libgcrypt could be extended to provide such a service.
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With the current scheme it is easy to retrieve the cached entries
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if access to Libgcrypt's memory is available. The encryption
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merely avoids grepping for clear texts in the memory. Nevertheless
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the encryption provides the necessary infrastructure to make it
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more secure. */
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static gcry_cipher_hd_t encryption_handle;
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struct secret_data_s {
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int totallen; /* This includes the padding and space for AESWRAP. */
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char data[1]; /* A string. */
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};
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typedef struct cache_item_s *ITEM;
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struct cache_item_s {
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ITEM next;
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time_t created;
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time_t accessed;
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int ttl; /* max. lifetime given in seconds, -1 one means infinite */
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struct secret_data_s *pw;
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cache_mode_t cache_mode;
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char key[1];
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};
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/* The cache himself. */
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static ITEM thecache;
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/* This function must be called once to initialize this module. It
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has to be done before a second thread is spawned. */
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void
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initialize_module_cache (void)
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{
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int err;
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err = npth_mutex_init (&encryption_lock, NULL);
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if (err)
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log_fatal ("error initializing cache module: %s\n", strerror (err));
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}
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void
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deinitialize_module_cache (void)
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{
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gcry_cipher_close (encryption_handle);
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encryption_handle = NULL;
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}
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/* We do the encryption init on the fly. We can't do it in the module
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init code because that is run before we listen for connections and
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in case we are started on demand by gpg etc. it will only wait for
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a few seconds to decide whether the agent may now accept
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connections. Thus we should get into listen state as soon as
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possible. */
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static gpg_error_t
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init_encryption (void)
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{
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gpg_error_t err;
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void *key;
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int res;
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if (encryption_handle)
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return 0; /* Shortcut - Already initialized. */
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res = npth_mutex_lock (&encryption_lock);
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if (res)
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log_fatal ("failed to acquire cache encryption mutex: %s\n", strerror (res));
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err = gcry_cipher_open (&encryption_handle, GCRY_CIPHER_AES128,
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GCRY_CIPHER_MODE_AESWRAP, GCRY_CIPHER_SECURE);
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if (!err)
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{
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key = gcry_random_bytes (ENCRYPTION_KEYSIZE, GCRY_STRONG_RANDOM);
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if (!key)
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err = gpg_error_from_syserror ();
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else
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{
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err = gcry_cipher_setkey (encryption_handle, key, ENCRYPTION_KEYSIZE);
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xfree (key);
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}
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if (err)
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{
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gcry_cipher_close (encryption_handle);
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encryption_handle = NULL;
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}
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}
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if (err)
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log_error ("error initializing cache encryption context: %s\n",
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gpg_strerror (err));
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res = npth_mutex_unlock (&encryption_lock);
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if (res)
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log_fatal ("failed to release cache encryption mutex: %s\n", strerror (res));
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return err? gpg_error (GPG_ERR_NOT_INITIALIZED) : 0;
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}
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static void
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release_data (struct secret_data_s *data)
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{
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xfree (data);
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}
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static gpg_error_t
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new_data (const char *string, struct secret_data_s **r_data)
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{
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gpg_error_t err;
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struct secret_data_s *d, *d_enc;
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size_t length;
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int total;
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int res;
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*r_data = NULL;
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err = init_encryption ();
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if (err)
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return err;
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length = strlen (string) + 1;
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/* We pad the data to 32 bytes so that it get more complicated
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finding something out by watching allocation patterns. This is
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usally not possible but we better assume nothing about our secure
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storage provider. To support the AESWRAP mode we need to add 8
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extra bytes as well. */
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total = (length + 8) + 32 - ((length+8) % 32);
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d = xtrymalloc_secure (sizeof *d + total - 1);
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if (!d)
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return gpg_error_from_syserror ();
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memcpy (d->data, string, length);
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d_enc = xtrymalloc (sizeof *d_enc + total - 1);
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if (!d_enc)
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{
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err = gpg_error_from_syserror ();
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xfree (d);
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return err;
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}
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d_enc->totallen = total;
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res = npth_mutex_lock (&encryption_lock);
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if (res)
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log_fatal ("failed to acquire cache encryption mutex: %s\n", strerror (err));
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err = gcry_cipher_encrypt (encryption_handle, d_enc->data, total,
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d->data, total - 8);
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xfree (d);
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res = npth_mutex_unlock (&encryption_lock);
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if (res)
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log_fatal ("failed to release cache encryption mutex: %s\n", strerror (res));
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if (err)
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{
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xfree (d_enc);
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return err;
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}
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*r_data = d_enc;
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return 0;
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}
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/* Check whether there are items to expire. */
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static void
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housekeeping (void)
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{
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ITEM r, rprev;
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time_t current = gnupg_get_time ();
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/* First expire the actual data */
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for (r=thecache; r; r = r->next)
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{
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if (r->pw && r->ttl >= 0 && r->accessed + r->ttl < current)
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{
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if (DBG_CACHE)
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log_debug (" expired `%s' (%ds after last access)\n",
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r->key, r->ttl);
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release_data (r->pw);
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r->pw = NULL;
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r->accessed = current;
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}
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}
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/* Second, make sure that we also remove them based on the created stamp so
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that the user has to enter it from time to time. */
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for (r=thecache; r; r = r->next)
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{
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unsigned long maxttl;
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switch (r->cache_mode)
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{
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case CACHE_MODE_SSH: maxttl = opt.max_cache_ttl_ssh; break;
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default: maxttl = opt.max_cache_ttl; break;
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}
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if (r->pw && r->created + maxttl < current)
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{
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if (DBG_CACHE)
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log_debug (" expired `%s' (%lus after creation)\n",
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r->key, opt.max_cache_ttl);
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release_data (r->pw);
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r->pw = NULL;
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r->accessed = current;
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}
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}
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/* Third, make sure that we don't have too many items in the list.
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Expire old and unused entries after 30 minutes */
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for (rprev=NULL, r=thecache; r; )
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{
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if (!r->pw && r->ttl >= 0 && r->accessed + 60*30 < current)
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{
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ITEM r2 = r->next;
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if (DBG_CACHE)
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log_debug (" removed `%s' (mode %d) (slot not used for 30m)\n",
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r->key, r->cache_mode);
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xfree (r);
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if (!rprev)
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thecache = r2;
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else
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rprev->next = r2;
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r = r2;
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}
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else
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{
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rprev = r;
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r = r->next;
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}
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}
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}
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void
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agent_flush_cache (void)
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{
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ITEM r;
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if (DBG_CACHE)
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log_debug ("agent_flush_cache\n");
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for (r=thecache; r; r = r->next)
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{
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if (r->pw)
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{
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if (DBG_CACHE)
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log_debug (" flushing `%s'\n", r->key);
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release_data (r->pw);
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r->pw = NULL;
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r->accessed = 0;
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}
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}
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}
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/* Store the string DATA in the cache under KEY and mark it with a
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maximum lifetime of TTL seconds. If there is already data under
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this key, it will be replaced. Using a DATA of NULL deletes the
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entry. A TTL of 0 is replaced by the default TTL and a TTL of -1
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set infinite timeout. CACHE_MODE is stored with the cache entry
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and used to select different timeouts. */
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int
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agent_put_cache (const char *key, cache_mode_t cache_mode,
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const char *data, int ttl)
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{
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gpg_error_t err = 0;
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ITEM r;
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if (DBG_CACHE)
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log_debug ("agent_put_cache `%s' (mode %d) requested ttl=%d\n",
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key, cache_mode, ttl);
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housekeeping ();
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if (!ttl)
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{
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switch(cache_mode)
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{
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case CACHE_MODE_SSH: ttl = opt.def_cache_ttl_ssh; break;
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default: ttl = opt.def_cache_ttl; break;
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}
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}
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if ((!ttl && data) || cache_mode == CACHE_MODE_IGNORE)
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return 0;
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for (r=thecache; r; r = r->next)
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{
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if (((cache_mode != CACHE_MODE_USER
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&& cache_mode != CACHE_MODE_NONCE)
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|| r->cache_mode == cache_mode)
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&& !strcmp (r->key, key))
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break;
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}
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if (r) /* Replace. */
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{
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if (r->pw)
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{
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release_data (r->pw);
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r->pw = NULL;
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}
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if (data)
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{
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r->created = r->accessed = gnupg_get_time ();
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r->ttl = ttl;
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r->cache_mode = cache_mode;
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err = new_data (data, &r->pw);
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if (err)
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log_error ("error replacing cache item: %s\n", gpg_strerror (err));
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}
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}
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else if (data) /* Insert. */
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{
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r = xtrycalloc (1, sizeof *r + strlen (key));
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if (!r)
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err = gpg_error_from_syserror ();
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else
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{
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strcpy (r->key, key);
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r->created = r->accessed = gnupg_get_time ();
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r->ttl = ttl;
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r->cache_mode = cache_mode;
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err = new_data (data, &r->pw);
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if (err)
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xfree (r);
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else
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{
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r->next = thecache;
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thecache = r;
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}
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}
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if (err)
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log_error ("error inserting cache item: %s\n", gpg_strerror (err));
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}
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return err;
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}
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/* Try to find an item in the cache. Note that we currently don't
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make use of CACHE_MODE except for CACHE_MODE_NONCE and
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CACHE_MODE_USER. */
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char *
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agent_get_cache (const char *key, cache_mode_t cache_mode)
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{
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gpg_error_t err;
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ITEM r;
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char *value = NULL;
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int res;
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if (cache_mode == CACHE_MODE_IGNORE)
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return NULL;
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if (DBG_CACHE)
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log_debug ("agent_get_cache `%s' (mode %d) ...\n", key, cache_mode);
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housekeeping ();
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for (r=thecache; r; r = r->next)
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{
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if (r->pw
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&& ((cache_mode != CACHE_MODE_USER
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&& cache_mode != CACHE_MODE_NONCE)
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|| r->cache_mode == cache_mode)
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&& !strcmp (r->key, key))
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{
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r->accessed = gnupg_get_time ();
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if (DBG_CACHE)
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log_debug ("... hit\n");
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if (r->pw->totallen < 32)
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err = gpg_error (GPG_ERR_INV_LENGTH);
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else if ((err = init_encryption ()))
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;
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else if (!(value = xtrymalloc_secure (r->pw->totallen - 8)))
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err = gpg_error_from_syserror ();
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else
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{
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res = npth_mutex_lock (&encryption_lock);
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if (res)
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log_fatal ("failed to acquire cache encryption mutex: %s\n",
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strerror (res));
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err = gcry_cipher_decrypt (encryption_handle,
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value, r->pw->totallen - 8,
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r->pw->data, r->pw->totallen);
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res = npth_mutex_unlock (&encryption_lock);
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if (res)
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log_fatal ("failed to release cache encryption mutex: %s\n",
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strerror (res));
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}
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if (err)
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{
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xfree (value);
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value = NULL;
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log_error ("retrieving cache entry `%s' failed: %s\n",
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key, gpg_strerror (err));
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}
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return value;
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}
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}
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if (DBG_CACHE)
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log_debug ("... miss\n");
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return NULL;
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}
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