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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 DCDEEC3A5A8 for ; Sun, 1 Sep 2019 00:07:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AE14A22D37 for ; Sun, 1 Sep 2019 00:07:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1567296469; bh=P5RbwRHQDN4mj8PbOE7mNbYp6W1+Z0WX/Kbt1x30H3U=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=0noth+J1gkG1mcgDX0ECcHfcusIJycIcyyb/v8hC44qlO63oO7vp/8TlETEG6FTi1 8FneOXWrc5OGT1ylB5CSHhUSCEq09G9E+yQlxOWDzkCEOuDXJIizm2kA+mccjBa0sI E2R77Gh6QtGx3xLMzI5jCQotCrqpKLKJTDXNCyzM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728587AbfIAAHt (ORCPT ); Sat, 31 Aug 2019 20:07:49 -0400 Received: from mail.kernel.org ([198.145.29.99]:58552 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726150AbfIAAHs (ORCPT ); Sat, 31 Aug 2019 20:07:48 -0400 Received: from localhost (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 99E1821874; Sun, 1 Sep 2019 00:07:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1567296467; bh=P5RbwRHQDN4mj8PbOE7mNbYp6W1+Z0WX/Kbt1x30H3U=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=nIodCGlvlGmztTC9dA21Btd7algx1Eqt2oPUvJmufwJ64JYkfGVoK8AE/MFX3Q88e fhLiqeERD09ylTAMrwLQklegzsoL2x326rRqeYwHMOU1/6zGfnHbGwp1oOVG9Ap7wp EvcGfXg0YPf/bR+tw0zt2cQ1JtLxpxHkTWAIp0OM= Date: Sat, 31 Aug 2019 20:07:46 -0400 From: Sasha Levin To: Matthieu Baerts Cc: Tim Froidcoeur , aprout@ll.mit.edu, cpaasch@apple.com, davem@davemloft.net, edumazet@google.com, gregkh@linuxfoundation.org, jonathan.lemon@gmail.com, jtl@netflix.com, linux-kernel@vger.kernel.org, mkubecek@suse.cz, ncardwell@google.com, stable@vger.kernel.org, ycheng@google.com, netdev@vger.kernel.org Subject: Re: [PATCH 4.14] tcp: fix tcp_rtx_queue_tail in case of empty retransmit queue Message-ID: <20190901000746.GA5281@sasha-vm> References: <529376a4-cf63-f225-ce7c-4747e9966938@tessares.net> <20190824060351.3776-1-tim.froidcoeur@tessares.net> <20190831122036.GY5281@sasha-vm> <35cd974b-2b31-4f86-d53d-8e9516d4077e@tessares.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <35cd974b-2b31-4f86-d53d-8e9516d4077e@tessares.net> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Aug 31, 2019 at 03:14:35PM +0200, Matthieu Baerts wrote: >Hi Sasha, > >Thank you for your reply! > >On 31/08/2019 14:20, Sasha Levin wrote: >> On Sat, Aug 24, 2019 at 08:03:51AM +0200, Tim Froidcoeur wrote: >>> Commit 8c3088f895a0 ("tcp: be more careful in tcp_fragment()") >>> triggers following stack trace: >>> >>> [25244.848046] kernel BUG at ./include/linux/skbuff.h:1406! >>> [25244.859335] RIP: 0010:skb_queue_prev+0x9/0xc >>> [25244.888167] Call Trace: >>> [25244.889182]  >>> [25244.890001]  tcp_fragment+0x9c/0x2cf >>> [25244.891295]  tcp_write_xmit+0x68f/0x988 >>> [25244.892732]  __tcp_push_pending_frames+0x3b/0xa0 >>> [25244.894347]  tcp_data_snd_check+0x2a/0xc8 >>> [25244.895775]  tcp_rcv_established+0x2a8/0x30d >>> [25244.897282]  tcp_v4_do_rcv+0xb2/0x158 >>> [25244.898666]  tcp_v4_rcv+0x692/0x956 >>> [25244.899959]  ip_local_deliver_finish+0xeb/0x169 >>> [25244.901547]  __netif_receive_skb_core+0x51c/0x582 >>> [25244.903193]  ? inet_gro_receive+0x239/0x247 >>> [25244.904756]  netif_receive_skb_internal+0xab/0xc6 >>> [25244.906395]  napi_gro_receive+0x8a/0xc0 >>> [25244.907760]  receive_buf+0x9a1/0x9cd >>> [25244.909160]  ? load_balance+0x17a/0x7b7 >>> [25244.910536]  ? vring_unmap_one+0x18/0x61 >>> [25244.911932]  ? detach_buf+0x60/0xfa >>> [25244.913234]  virtnet_poll+0x128/0x1e1 >>> [25244.914607]  net_rx_action+0x12a/0x2b1 >>> [25244.915953]  __do_softirq+0x11c/0x26b >>> [25244.917269]  ? handle_irq_event+0x44/0x56 >>> [25244.918695]  irq_exit+0x61/0xa0 >>> [25244.919947]  do_IRQ+0x9d/0xbb >>> [25244.921065]  common_interrupt+0x85/0x85 >>> [25244.922479]  >>> >>> tcp_rtx_queue_tail() (called by tcp_fragment()) can call >>> tcp_write_queue_prev() on the first packet in the queue, which will >>> trigger >>> the BUG in tcp_write_queue_prev(), because there is no previous packet. >>> >>> This happens when the retransmit queue is empty, for example in case of a >>> zero window. >>> >>> Patch is needed for 4.4, 4.9 and 4.14 stable branches. >> >> There needs to be a better explanation of why it's not needed >> upstream... > >Commit 8c3088f895a0 ("tcp: be more careful in tcp_fragment()") was not a >simple cherry-pick of the original one from master (b617158dc096) >because there is a specific TCP rtx queue only since v4.15. For more >details, please see the commit message of b617158dc096 ("tcp: be more >careful in tcp_fragment()"). > >The BUG() is hit due to the specific code added to versions older than >v4.15. The comment in skb_queue_prev() (include/linux/skbuff.h:1406), >just before the BUG_ON() somehow suggests to add a check before using >it, what Tim did. > >In master, this code path causing the issue will not be taken because >the implementation of tcp_rtx_queue_tail() is different: > > tcp_fragment() → tcp_rtx_queue_tail() → tcp_write_queue_prev() → >skb_queue_prev() → BUG_ON() > >Because this patch is specific to versions older than the two last >stable ones but still linked to the network architecture, who can review >and approve it? :) Thanks for the explanation. I've changed the commit message to include this explanation and queued it for 4.4, 4.9 and 4.14. -- Thanks, Sasha