1 files changed, 530 insertions, 0 deletions
diff --git a/agent/cache.c b/agent/cache.c
new file mode 100644
index 0000000..238b6e2
--- /dev/null
+++ b/agent/cache.c
@@ -0,0 +1,530 @@
+/* cache.c - keep a cache of passphrases
+ * Copyright (C) 2002, 2010 Free Software Foundation, Inc.
+ *
+ * This file is part of GnuPG.
+ *
+ * GnuPG is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * GnuPG is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <config.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <time.h>
+#include <assert.h>
+#include <npth.h>
+
+#include "agent.h"
+
+/* The size of the encryption key in bytes.  */
+#define ENCRYPTION_KEYSIZE (128/8)
+
+/* A mutex used to serialize access to the cache.  */
+static npth_mutex_t cache_lock;
+/* The encryption context.  This is the only place where the
+   encryption key for all cached entries is available.  It would be nice
+   to keep this (or just the key) in some hardware device, for example
+   a TPM.  Libgcrypt could be extended to provide such a service.
+   With the current scheme it is easy to retrieve the cached entries
+   if access to Libgcrypt's memory is available.  The encryption
+   merely avoids grepping for clear texts in the memory.  Nevertheless
+   the encryption provides the necessary infrastructure to make it
+   more secure.  */
+static gcry_cipher_hd_t encryption_handle;
+
+
+struct secret_data_s {
+  int  totallen; /* This includes the padding and space for AESWRAP. */
+  char data[1];  /* A string.  */
+};
+
+typedef struct cache_item_s *ITEM;
+struct cache_item_s {
+  ITEM next;
+  time_t created;
+  time_t accessed;
+  int ttl;  /* max. lifetime given in seconds, -1 one means infinite */
+  struct secret_data_s *pw;
+  cache_mode_t cache_mode;
+  int restricted;  /* The value of ctrl->restricted is part of the key.  */
+  char key[1];
+};
+
+/* The cache himself.  */
+static ITEM thecache;
+
+/* NULL or the last cache key stored by agent_store_cache_hit.  */
+static char *last_stored_cache_key;
+
+
+/* This function must be called once to initialize this module. It
+   has to be done before a second thread is spawned.  */
+void
+initialize_module_cache (void)
+{
+  int err;
+
+  err = npth_mutex_init (&cache_lock, NULL);
+
+  if (err)
+    log_fatal ("error initializing cache module: %s\n", strerror (err));
+}
+
+
+void
+deinitialize_module_cache (void)
+{
+  gcry_cipher_close (encryption_handle);
+  encryption_handle = NULL;
+}
+
+
+/* We do the encryption init on the fly.  We can't do it in the module
+   init code because that is run before we listen for connections and
+   in case we are started on demand by gpg etc. it will only wait for
+   a few seconds to decide whether the agent may now accept
+   connections.  Thus we should get into listen state as soon as
+   possible.  */
+static gpg_error_t
+init_encryption (void)
+{
+  gpg_error_t err;
+  void *key;
+
+  if (encryption_handle)
+    return 0; /* Shortcut - Already initialized.  */
+
+  err = gcry_cipher_open (&encryption_handle, GCRY_CIPHER_AES128,
+                          GCRY_CIPHER_MODE_AESWRAP, GCRY_CIPHER_SECURE);
+  if (!err)
+    {
+      key = gcry_random_bytes (ENCRYPTION_KEYSIZE, GCRY_STRONG_RANDOM);
+      if (!key)
+        err = gpg_error_from_syserror ();
+      else
+        {
+          err = gcry_cipher_setkey (encryption_handle, key, ENCRYPTION_KEYSIZE);
+          xfree (key);
+        }
+      if (err)
+        {
+          gcry_cipher_close (encryption_handle);
+          encryption_handle = NULL;
+        }
+    }
+  if (err)
+    log_error ("error initializing cache encryption context: %s\n",
+               gpg_strerror (err));
+
+  return err? gpg_error (GPG_ERR_NOT_INITIALIZED) : 0;
+}
+
+
+
+static void
+release_data (struct secret_data_s *data)
+{
+   xfree (data);
+}
+
+static gpg_error_t
+new_data (const char *string, struct secret_data_s **r_data)
+{
+  gpg_error_t err;
+  struct secret_data_s *d, *d_enc;
+  size_t length;
+  int total;
+
+  *r_data = NULL;
+
+  err = init_encryption ();
+  if (err)
+    return err;
+
+  length = strlen (string) + 1;
+
+  /* We pad the data to 32 bytes so that it get more complicated
+     finding something out by watching allocation patterns.  This is
+     usually not possible but we better assume nothing about our secure
+     storage provider.  To support the AESWRAP mode we need to add 8
+     extra bytes as well. */
+  total = (length + 8) + 32 - ((length+8) % 32);
+
+  d = xtrymalloc_secure (sizeof *d + total - 1);
+  if (!d)
+    return gpg_error_from_syserror ();
+  memcpy (d->data, string, length);
+
+  d_enc = xtrymalloc (sizeof *d_enc + total - 1);
+  if (!d_enc)
+    {
+      err = gpg_error_from_syserror ();
+      xfree (d);
+      return err;
+    }
+
+  d_enc->totallen = total;
+  err = gcry_cipher_encrypt (encryption_handle, d_enc->data, total,
+                             d->data, total - 8);
+  xfree (d);
+  if (err)
+    {
+      xfree (d_enc);
+      return err;
+    }
+  *r_data = d_enc;
+  return 0;
+}
+
+
+
+/* Check whether there are items to expire.  */
+static void
+housekeeping (void)
+{
+  ITEM r, rprev;
+  time_t current = gnupg_get_time ();
+
+  /* First expire the actual data */
+  for (r=thecache; r; r = r->next)
+    {
+      if (r->pw && r->ttl >= 0 && r->accessed + r->ttl < current)
+        {
+          if (DBG_CACHE)
+            log_debug ("  expired '%s'.%d (%ds after last access)\n",
+                       r->key, r->restricted, r->ttl);
+          release_data (r->pw);
+          r->pw = NULL;
+          r->accessed = current;
+        }
+    }
+
+  /* Second, make sure that we also remove them based on the created stamp so
+     that the user has to enter it from time to time. */
+  for (r=thecache; r; r = r->next)
+    {
+      unsigned long maxttl;
+
+      switch (r->cache_mode)
+        {
+        case CACHE_MODE_SSH: maxttl = opt.max_cache_ttl_ssh; break;
+        default: maxttl = opt.max_cache_ttl; break;
+        }
+      if (r->pw && r->created + maxttl < current)
+        {
+          if (DBG_CACHE)
+            log_debug ("  expired '%s'.%d (%lus after creation)\n",
+                       r->key, r->restricted, opt.max_cache_ttl);
+          release_data (r->pw);
+          r->pw = NULL;
+          r->accessed = current;
+        }
+    }
+
+  /* Third, make sure that we don't have too many items in the list.
+   * Expire old and unused entries after 30 minutes.  */
+  for (rprev=NULL, r=thecache; r; )
+    {
+      if (!r->pw && r->ttl >= 0 && r->accessed + 60*30 < current)
+        {
+          ITEM r2 = r->next;
+          if (DBG_CACHE)
+            log_debug ("  removed '%s'.%d (mode %d) (slot not used for 30m)\n",
+                       r->key, r->restricted, r->cache_mode);
+          xfree (r);
+          if (!rprev)
+            thecache = r2;
+          else
+            rprev->next = r2;
+          r = r2;
+        }
+      else
+        {
+          rprev = r;
+          r = r->next;
+        }
+    }
+}
+
+
+void
+agent_cache_housekeeping (void)
+{
+  int res;
+
+  if (DBG_CACHE)
+    log_debug ("agent_cache_housekeeping\n");
+
+  res = npth_mutex_lock (&cache_lock);
+  if (res)
+    log_fatal ("failed to acquire cache mutex: %s\n", strerror (res));
+
+  housekeeping ();
+
+  res = npth_mutex_unlock (&cache_lock);
+  if (res)
+    log_fatal ("failed to release cache mutex: %s\n", strerror (res));
+}
+
+
+void
+agent_flush_cache (void)
+{
+  ITEM r;
+  int res;
+
+  if (DBG_CACHE)
+    log_debug ("agent_flush_cache\n");
+
+  res = npth_mutex_lock (&cache_lock);
+  if (res)
+    log_fatal ("failed to acquire cache mutex: %s\n", strerror (res));
+
+  for (r=thecache; r; r = r->next)
+    {
+      if (r->pw)
+        {
+          if (DBG_CACHE)
+            log_debug ("  flushing '%s'.%d\n", r->key, r->restricted);
+          release_data (r->pw);
+          r->pw = NULL;
+          r->accessed = 0;
+        }
+    }
+
+  res = npth_mutex_unlock (&cache_lock);
+  if (res)
+    log_fatal ("failed to release cache mutex: %s\n", strerror (res));
+}
+
+
+/* Compare two cache modes.  */
+static int
+cache_mode_equal (cache_mode_t a, cache_mode_t b)
+{
+  /* CACHE_MODE_ANY matches any mode other than CACHE_MODE_IGNORE.  */
+  return ((a == CACHE_MODE_ANY && b != CACHE_MODE_IGNORE)
+          || (b == CACHE_MODE_ANY && a != CACHE_MODE_IGNORE) || a == b);
+}
+
+
+/* Store the string DATA in the cache under KEY and mark it with a
+   maximum lifetime of TTL seconds.  If there is already data under
+   this key, it will be replaced.  Using a DATA of NULL deletes the
+   entry.  A TTL of 0 is replaced by the default TTL and a TTL of -1
+   set infinite timeout.  CACHE_MODE is stored with the cache entry
+   and used to select different timeouts.  */
+int
+agent_put_cache (ctrl_t ctrl, const char *key, cache_mode_t cache_mode,
+                 const char *data, int ttl)
+{
+  gpg_error_t err = 0;
+  ITEM r;
+  int res;
+  int restricted = ctrl? ctrl->restricted : -1;
+
+  res = npth_mutex_lock (&cache_lock);
+  if (res)
+    log_fatal ("failed to acquire cache mutex: %s\n", strerror (res));
+
+  if (DBG_CACHE)
+    log_debug ("agent_put_cache '%s'.%d (mode %d) requested ttl=%d\n",
+               key, restricted, cache_mode, ttl);
+  housekeeping ();
+
+  if (!ttl)
+    {
+      switch(cache_mode)
+        {
+        case CACHE_MODE_SSH: ttl = opt.def_cache_ttl_ssh; break;
+        default: ttl = opt.def_cache_ttl; break;
+        }
+    }
+  if ((!ttl && data) || cache_mode == CACHE_MODE_IGNORE)
+    goto out;
+
+  for (r=thecache; r; r = r->next)
+    {
+      if (((cache_mode != CACHE_MODE_USER
+            && cache_mode != CACHE_MODE_NONCE)
+           || cache_mode_equal (r->cache_mode, cache_mode))
+          && r->restricted == restricted
+          && !strcmp (r->key, key))
+        break;
+    }
+  if (r) /* Replace.  */
+    {
+      if (r->pw)
+        {
+          release_data (r->pw);
+          r->pw = NULL;
+        }
+      if (data)
+        {
+          r->created = r->accessed = gnupg_get_time ();
+          r->ttl = ttl;
+          r->cache_mode = cache_mode;
+          err = new_data (data, &r->pw);
+          if (err)
+            log_error ("error replacing cache item: %s\n", gpg_strerror (err));
+        }
+    }
+  else if (data) /* Insert.  */
+    {
+      r = xtrycalloc (1, sizeof *r + strlen (key));
+      if (!r)
+        err = gpg_error_from_syserror ();
+      else
+        {
+          strcpy (r->key, key);
+          r->restricted = restricted;
+          r->created = r->accessed = gnupg_get_time ();
+          r->ttl = ttl;
+          r->cache_mode = cache_mode;
+          err = new_data (data, &r->pw);
+          if (err)
+            xfree (r);
+          else
+            {
+              r->next = thecache;
+              thecache = r;
+            }
+        }
+      if (err)
+        log_error ("error inserting cache item: %s\n", gpg_strerror (err));
+    }
+
+ out:
+  res = npth_mutex_unlock (&cache_lock);
+  if (res)
+    log_fatal ("failed to release cache mutex: %s\n", strerror (res));
+
+  return err;
+}
+
+
+/* Try to find an item in the cache.  Note that we currently don't
+   make use of CACHE_MODE except for CACHE_MODE_NONCE and
+   CACHE_MODE_USER.  */
+char *
+agent_get_cache (ctrl_t ctrl, const char *key, cache_mode_t cache_mode)
+{
+  gpg_error_t err;
+  ITEM r;
+  char *value = NULL;
+  int res;
+  int last_stored = 0;
+  int restricted = ctrl? ctrl->restricted : -1;
+
+  if (cache_mode == CACHE_MODE_IGNORE)
+    return NULL;
+
+  res = npth_mutex_lock (&cache_lock);
+  if (res)
+    log_fatal ("failed to acquire cache mutex: %s\n", strerror (res));
+
+  if (!key)
+    {
+      key = last_stored_cache_key;
+      if (!key)
+        goto out;
+      last_stored = 1;
+    }
+
+  if (DBG_CACHE)
+    log_debug ("agent_get_cache '%s'.%d (mode %d)%s ...\n",
+               key, ctrl->restricted, cache_mode,
+               last_stored? " (stored cache key)":"");
+  housekeeping ();
+
+  for (r=thecache; r; r = r->next)
+    {
+      if (r->pw
+          && ((cache_mode != CACHE_MODE_USER
+               && cache_mode != CACHE_MODE_NONCE)
+              || cache_mode_equal (r->cache_mode, cache_mode))
+          && r->restricted == restricted
+          && !strcmp (r->key, key))
+        {
+          /* Note: To avoid races KEY may not be accessed anymore below.  */
+          r->accessed = gnupg_get_time ();
+          if (DBG_CACHE)
+            log_debug ("... hit\n");
+          if (r->pw->totallen < 32)
+            err = gpg_error (GPG_ERR_INV_LENGTH);
+          else if ((err = init_encryption ()))
+            ;
+          else if (!(value = xtrymalloc_secure (r->pw->totallen - 8)))
+            err = gpg_error_from_syserror ();
+          else
+            {
+              err = gcry_cipher_decrypt (encryption_handle,
+                                         value, r->pw->totallen - 8,
+                                         r->pw->data, r->pw->totallen);
+            }
+          if (err)
+            {
+              xfree (value);
+              value = NULL;
+              log_error ("retrieving cache entry '%s'.%d failed: %s\n",
+                         key, restricted, gpg_strerror (err));
+            }
+          break;
+        }
+    }
+  if (DBG_CACHE && value == NULL)
+    log_debug ("... miss\n");
+
+ out:
+  res = npth_mutex_unlock (&cache_lock);
+  if (res)
+    log_fatal ("failed to release cache mutex: %s\n", strerror (res));
+
+  return value;
+}
+
+
+/* Store the key for the last successful cache hit.  That value is
+   used by agent_get_cache if the requested KEY is given as NULL.
+   NULL may be used to remove that key. */
+void
+agent_store_cache_hit (const char *key)
+{
+  char *new;
+  char *old;
+
+  /* To make sure the update is atomic under the non-preemptive thread
+   * model, we must make sure not to surrender control to a different
+   * thread.  Therefore, we avoid calling the allocator during the
+   * update.
+   *
+   * Background: xtrystrdup uses gcry_strdup which may use the secure
+   * memory allocator of Libgcrypt.  That allocator takes locks and
+   * since version 1.14 libgpg-error is nPth aware and thus taking a
+   * lock may now lead to thread switch.  Note that this only happens
+   * when secure memory is _allocated_ (the standard allocator uses
+   * malloc which is not nPth aware) but not when calling _xfree_
+   * because gcry_free needs to check whether the pointer is in secure
+   * memory and thus needs to take a lock.
+   */
+  new = key ? xtrystrdup (key) : NULL;
+
+  /* Atomic update.  */
+  old = last_stored_cache_key;
+  last_stored_cache_key = new;
+  /* Done.  */
+
+  xfree (old);
+}