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 X-Spam-Level: X-Spam-Status: No, score=-3.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_NEOMUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5A988C43219 for ; Fri, 26 Apr 2019 17:06:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2F818206E0 for ; Fri, 26 Apr 2019 17:06:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726184AbfDZRGy (ORCPT ); Fri, 26 Apr 2019 13:06:54 -0400 Received: from mail.us.es ([193.147.175.20]:33286 "EHLO mail.us.es" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726068AbfDZRGx (ORCPT ); Fri, 26 Apr 2019 13:06:53 -0400 Received: from antivirus1-rhel7.int (unknown [192.168.2.11]) by mail.us.es (Postfix) with ESMTP id 0BAAA1031E4 for ; Fri, 26 Apr 2019 19:06:52 +0200 (CEST) Received: from antivirus1-rhel7.int (localhost [127.0.0.1]) by antivirus1-rhel7.int (Postfix) with ESMTP id F1885DA707 for ; Fri, 26 Apr 2019 19:06:51 +0200 (CEST) Received: by antivirus1-rhel7.int (Postfix, from userid 99) id E75EADA706; Fri, 26 Apr 2019 19:06:51 +0200 (CEST) Received: from antivirus1-rhel7.int (localhost [127.0.0.1]) by antivirus1-rhel7.int (Postfix) with ESMTP id E05C6DA702; Fri, 26 Apr 2019 19:06:49 +0200 (CEST) Received: from 192.168.1.97 (192.168.1.97) by antivirus1-rhel7.int (F-Secure/fsigk_smtp/550/antivirus1-rhel7.int); Fri, 26 Apr 2019 19:06:49 +0200 (CEST) X-Virus-Status: clean(F-Secure/fsigk_smtp/550/antivirus1-rhel7.int) Received: from us.es (sys.soleta.eu [212.170.55.40]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) (Authenticated sender: 1984lsi) by entrada.int (Postfix) with ESMTPSA id BB83C4265A31; Fri, 26 Apr 2019 19:06:49 +0200 (CEST) Date: Fri, 26 Apr 2019 19:06:49 +0200 X-SMTPAUTHUS: auth mail.us.es From: Pablo Neira Ayuso To: Johannes Berg Cc: netdev@vger.kernel.org Subject: Re: [RFC] netlink: limit recursion depth in policy validation Message-ID: <20190426170649.5aa6b64464zmeeze@salvia> References: <20190405212414.24184-1-johannes@sipsolutions.net> <20190426165710.o4dpxzq5futnspu7@salvia> <7be848796a1f5552e611e131c8613408c128bfc8.camel@sipsolutions.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7be848796a1f5552e611e131c8613408c128bfc8.camel@sipsolutions.net> User-Agent: NeoMutt/20170113 (1.7.2) X-Virus-Scanned: ClamAV using ClamSMTP Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Fri, Apr 26, 2019 at 07:03:10PM +0200, Johannes Berg wrote: > On Fri, 2019-04-26 at 18:57 +0200, Pablo Neira Ayuso wrote: > > > > > +/* > > > + * Nested policies might refer back to the original > > > + * policy in some cases, and userspace could try to > > > + * abuse that and recurse by nesting in the right > > > + * ways. Limit recursion to avoid this problem. > > > + */ > > > +#define MAX_POLICY_RECURSION_DEPTH 10 > > > > In your policy description approach, you iterate over the policy > > structures. How do you deal with this recursions from there? > > Well, check out the code :-) > > It doesn't actually recurse. What it does is build a list of policies > that are reachable from the root policy and each policy in the list. So > basically, there we do: > > list = [root policy] > list_len = 1 > i = 0 > > walk_policy(policy) > { > for_each_policy_entry(entry, policy) { > nested = nested_policy_or_null(entry); > if (nested) { > list[i] = nested; > list_len += 1 > } > } > } > > while (i < list_len) { > walk_policy(list[i]); > i++; > } > > Then, we walk the list again: > > for (i = 0; i < list_len; i++) { > for_each_policy_entry(entry, list[i]) { > send_entry_to_userspace(i, entry); // mark it as occurring in policy i > } > } > > > This basically flattens the whole thing. > > Obviously, the walking may allocate some memory, and the last loop to > send it out isn't actually a loop like that because it's a netlink dump > with each entry being in a separate netlink message, but that's the gist > of it. I see, following this approach, I can just remove the duplicated code in my netlink description stuff by using the list of policy structures.