ldb: make ldb module programming less error prone

When a top level method in a module returns an error, it is supposed
to call ldb_module_done(). We ran across a case where this wasn't
done, and then found that in fact that are hundreds of similar cases
in our modules. It took Andrew and I a full day to work out that this
was the cause of a subtle segv in another part of the code.

To try to prevent this happening again, this patch changes
ldb_next_request() to catch the error by checking if a module
returning an error has called ldb_module_done(). If it hasn't then the
call is made on behalf of the module.

2 files changed, 17 insertions, 0 deletions

diff --git a/source4/lib/ldb/common/ldb_modules.c b/source4/lib/ldb/common/ldb_modules.c
index b792daa913..79a97cabed 100644
--- a/source4/lib/ldb/common/ldb_modules.c
+++ b/source4/lib/ldb/common/ldb_modules.c
@@ -577,6 +577,17 @@ int ldb_next_request(struct ldb_module *module, struct ldb_request *request)
 		/* Set a default error string, to place the blame somewhere */
 		ldb_asprintf_errstring(module->ldb, "error in module %s: %s (%d)", module->ops->name, ldb_strerror(ret), ret);
 	}
+
+	if (!(request->handle->flags & LDB_HANDLE_FLAG_DONE_CALLED)) {
+		/* It is _extremely_ common that a module returns a
+		 * failure without calling ldb_module_done(), but that
+		 * guarantees we will end up hanging in
+		 * ldb_wait(). This fixes it without having to rewrite
+		 * all our modules, and leaves us one less sharp
+		 * corner for module developers to cut themselves on 
+		 */
+		ldb_module_done(request, NULL, NULL, ret);
+	}
 	return ret;
 }
 
@@ -629,6 +640,7 @@ struct ldb_handle *ldb_handle_new(TALLOC_CTX *mem_ctx, struct ldb_context *ldb)
 	h->status = LDB_SUCCESS;
 	h->state = LDB_ASYNC_INIT;
 	h->ldb = ldb;
+	h->flags = 0;
 
 	return h;
 }
@@ -715,6 +727,8 @@ int ldb_module_done(struct ldb_request *req,
 	ares->response = talloc_steal(ares, response);
 	ares->error = error;
 
+	req->handle->flags |= LDB_HANDLE_FLAG_DONE_CALLED;
+
 	req->callback(req, ares);
 	return error;
 }
diff --git a/source4/lib/ldb/include/ldb_private.h b/source4/lib/ldb/include/ldb_private.h
index 3cda9a3e33..a70d9c704d 100644
--- a/source4/lib/ldb/include/ldb_private.h
+++ b/source4/lib/ldb/include/ldb_private.h
@@ -47,10 +47,13 @@ struct ldb_module_ops;
 
 struct ldb_backend_ops;
 
+#define LDB_HANDLE_FLAG_DONE_CALLED 1
+
 struct ldb_handle {
 	int status;
 	enum ldb_state state;
 	struct ldb_context *ldb;
+	unsigned flags;
 };
 
 /* basic module structure */