From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 676C4C433F5 for ; Thu, 2 Dec 2021 13:54:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1358376AbhLBN5c (ORCPT ); Thu, 2 Dec 2021 08:57:32 -0500 Received: from mail.netfilter.org ([217.70.188.207]:56558 "EHLO mail.netfilter.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1358374AbhLBN5a (ORCPT ); Thu, 2 Dec 2021 08:57:30 -0500 Received: from netfilter.org (unknown [78.30.32.163]) by mail.netfilter.org (Postfix) with ESMTPSA id 1C6A8607DF; Thu, 2 Dec 2021 14:51:49 +0100 (CET) Date: Thu, 2 Dec 2021 14:54:02 +0100 From: Pablo Neira Ayuso To: Eugene Crosser Cc: "netfilter-devel@vger.kernel.org" Subject: Re: Suboptimal error handling in libnftables Message-ID: References: <45b08de8-13d7-b30d-ca47-b44deeeff83a@average.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <45b08de8-13d7-b30d-ca47-b44deeeff83a@average.org> Precedence: bulk List-ID: X-Mailing-List: netfilter-devel@vger.kernel.org On Thu, Dec 02, 2021 at 02:16:12PM +0100, Eugene Crosser wrote: > Hello, > > there is read-from-the-socket loop in src/iface.c line 90 (function > iface_cache_update()), and it (and other places) call macro > netlink_init_error() to report error. The function behind the macro is > in src/netlink.c line 81, and it calls exit(NFT_EXIT_NONL) after writing > a message to stderr. > > I see two problems with this: > > 1. All read-from-the-socket functions should be run in a loop, repeating > if return code is -1 and errno is EINTR. I.e. EINTR should not be > treated as an error, but as a condition that requires retry. > > 2. Library functions are not supposed to call exit() (or abort() for > that matter). They are expected to return an error indication to the > caller, who may have its own strategy for handling error conditions. > > Case in point, we have a daemon (in Python) that uses bindings to > libnftables. It's a service responding to requests coming over a TCP > connection, and it takes care to intercept any error situations and > report them back. We discovered that under some conditions, it just > closes the socket and goes away. This being a daemon, stderr was not > immediately accessible; and even it it were, it is pretty hard to figure > where did the message "iface.c:98: Unable to initialize Netlink socket: > Interrupted system call" come from and why! This missing EINTR handling for iface_cache_update() is a bug, would you post a patch for this? > There is another function that calls exit(), __netlink_abi_error(). I > believe that even in such a harsh situation, exit() is not the right way > to handle it. ABI breakage between kernel and userspace should not ever happen.