[git] GnuPG - branch, master, updated. gnupg-2.1.18-17-ge175152

[by Justus Winter]

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- Log -----------------------------------------------------------------
commit e175152ef7515921635bf1e00383e812668d13fc
Author: Justus Winter <justus at g10code.com>
Date:   Wed Jan 25 13:51:57 2017 +0100

    agent: Fix double free.
    
    * agent/cache.c (agent_store_cache_hit): Make sure the update is
    atomic.
    --
    Previously, the function freed the last key, and duplicated the new
    key after doing that.  There is a chance, however, that calling the
    allocator surrenders control to a different thread, causing a double
    free if a different thread also calls this function.
    
    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.
    
    Signed-off-by: Justus Winter <justus at g10code.com>

diff --git a/agent/cache.c b/agent/cache.c
index f58eaea..2483682 100644
--- a/agent/cache.c
+++ b/agent/cache.c
@@ -475,6 +475,19 @@ agent_get_cache (const char *key, cache_mode_t cache_mode)
 void
 agent_store_cache_hit (const char *key)
 {
-  xfree (last_stored_cache_key);
-  last_stored_cache_key = key? xtrystrdup (key) : NULL;
+  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.  */
+  new = key ? xtrystrdup (key) : NULL;
+
+  /* Atomic update.  */
+  old = last_stored_cache_key;
+  last_stored_cache_key = new;
+  /* Done.  */
+
+  xfree (old);
 }

-----------------------------------------------------------------------

Summary of changes:
 agent/cache.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)


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