* 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@g10code.com>
(cherry picked from commit
e175152ef7515921635bf1e00383e812668d13fc)
Gbp-Pq: Name 0017-agent-Fix-double-free.patch
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);
}