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 897F3C433EF for ; Fri, 17 Jun 2022 00:16:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1379091AbiFQAQS (ORCPT ); Thu, 16 Jun 2022 20:16:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34964 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229832AbiFQAQP (ORCPT ); Thu, 16 Jun 2022 20:16:15 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2D20D17A9D for ; Thu, 16 Jun 2022 17:16:15 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id BA3CA618CF for ; Fri, 17 Jun 2022 00:16:14 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id ECC61C34114; Fri, 17 Jun 2022 00:16:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1655424974; bh=xT4O+qJMPr8aTmMsGWhlP651BE5VQl8C1eHSMvCHQqk=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=n+9z7bSkEV9GR/ayOqZbHAtCKXeQ0Y3d/xxzDHylFWpERW53yZhc0higyf7Md6bpL 64DsOjzE9RNKTwR2zpzTbcd9hKZWs9AxUvzGlpl4hnr9ZpFUglj6oF+JIhEABtumYo qCAeQ3O3TBoH2HVsyuooL1cadCVlRbvbBbqEbJfrZd4S8uoKdhfliX1LmH36RVRoDx MPzPj4vdRDz605pBHnPzX3URh2FLumHFcoFcL56vJs6rOBRANxAKWt+SoSgY+jYy42 gtlfCCFBRnrKYAU0J+nr1gkgWuAEFmnYQtzLeoW5xDpjcCsg7UbTeKKoJiSeFHePw2 CBfbG5lqRnr/w== Date: Thu, 16 Jun 2022 17:16:12 -0700 From: Jakub Kicinski To: Ismael Luceno Cc: "David S. Miller" , Paolo Abeni , David Ahern , "netdev@vger.kernel.org" Subject: Re: Netlink NLM_F_DUMP_INTR flag lost Message-ID: <20220616171612.66638e54@kernel.org> In-Reply-To: <20220616171016.56d4ec9c@pirotess> References: <20220615171113.7d93af3e@pirotess> <20220615090044.54229e73@kernel.org> <20220616171016.56d4ec9c@pirotess> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Thu, 16 Jun 2022 17:10:16 +0200 Ismael Luceno wrote: > On Wed, 15 Jun 2022 09:00:44 -0700 > Jakub Kicinski wrote: > > On Wed, 15 Jun 2022 17:11:13 +0200 Ismael Luceno wrote: > > > It seems a RTM_GETADDR request with AF_UNSPEC has a corner case > > > where the NLM_F_DUMP_INTR flag is lost. > > > > > > After a change in an address table, if a packet has been fully > > > filled just previous, and if the end of the table is found at the > > > same time, then the next packet should be flagged, which works fine > > > when it's NLMSG_DONE, but gets clobbered when another table is to > > > be dumped next. > > > > Could you describe how it gets clobbered? You mean that prev_seq gets > > updated somewhere without setting the flag or something overwrites > > nlmsg_flags? Or we set _INTR on an empty skb which never ends up > > getting sent? Or.. > > It seems to me that in most functions, but specifically in the case of > net/ipv4/devinet.c:in_dev_dump_addr or inet_netconf_dump_devconf, > nl_dump_check_consistent is called after each address/attribute is > dumped, meaning a hash table generation change happening just after it > adds an entry, if it also causes it to find the end of the table, > wouldn't be flagged. > > Adding an extra call at the end of all these functions should fix that, > and spill the flag into the next packet, but would that be correct? The whole _DUMP_INTR scheme does indeed seem to lack robustness. The update side changes the atomic after the update, and the read side validates it before. So there's plenty time for a race to happen. But I'm not sure if that's what you mean or you see more issues. > It seems this condition is flagged correctly when NLM_DONE is produced, > I couldn't see why, but I'm guessing another call to > nl_dump_check_consistent... > > Also, I noticed that in net/core/rtnetlink.c:rtnl_dump_all: > > if (idx > s_idx) { > memset(&cb->args[0], 0, sizeof(cb->args)); > cb->prev_seq = 0; > cb->seq = 0; > } > ret = dumpit(skb, cb); > > This also prevents it to be detect the condition when dumping the next > table, but that seems desirable... That's iterating over protocols, AFAICT, we don't guarantee consistency across protocols. > Am I grasping it correctly? > > Some functions like net/core/rtnetlink.c:rtnl_dump_ifinfo do call > nl_dump_check_consistent when finishing, but I'm seeing most others > don't do that, instead doing it only when adding an entry to the packet > (another example is: rtnl_stats_dump). > > Again, while adding the check at the end of each function would solve > these inconsistencies, it isn't so clear to me that spilling this flag > into the next packet when it's going to be from another table is a good > idea. > > It might make more sense to emit a new packet type just for the flag, > that way, in the sequence of packets, the client can reliably tell the > dump of which tables was interrupted, and make some decision based on > that, vs having to deem all tables affected... >