log_event_decoder: fixed corner case that caused double free

When a single event was read and the unpacked record data was copied to
the unpacked group record structure it would cause a double free when
destroying the decoder.

To handle this we need to ensure that the zone pointers in those
instances do not match or otherwise re-initialize one to avoid
performing the spurious free.

Signed-off-by: Leonardo Alminana <[email protected]>

Author: leonardo-albertovich

src/flb_log_event_decoder.c

@@ -146,6 +146,11 @@ void flb_log_event_decoder_destroy(struct flb_log_event_decoder *context)
 
     if (context != NULL) {
         if (context->initialized) {
+            if (context->unpacked_group_record.zone ==
+                context->unpacked_event.zone) {
+                msgpack_unpacked_init(&context->unpacked_event);
+            }
+
             msgpack_unpacked_destroy(&context->unpacked_group_record);
             msgpack_unpacked_destroy(&context->unpacked_empty_map);
             msgpack_unpacked_destroy(&context->unpacked_event);
@@ -322,6 +327,11 @@ int flb_log_event_decoder_next(struct flb_log_event_decoder *context,
         return context->last_result;
     }
 
+    if (context->unpacked_group_record.zone ==
+        context->unpacked_event.zone) {
+        msgpack_unpacked_init(&context->unpacked_event);
+    }
+
     previous_offset = context->offset;
     result = msgpack_unpack_next(&context->unpacked_event,
                                  context->buffer,
@@ -377,8 +387,6 @@ int flb_log_event_decoder_next(struct flb_log_event_decoder *context,
             }
 
             if (context->read_groups != FLB_TRUE) {
-                msgpack_unpacked_init(&context->unpacked_event);
-
                 memset(event, 0, sizeof(struct flb_log_event));
 
                 return flb_log_event_decoder_next(context, event);