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=-3.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 16F9BC352A2 for ; Thu, 6 Feb 2020 12:59:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E2693217F4 for ; Thu, 6 Feb 2020 12:59:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727556AbgBFM72 (ORCPT ); Thu, 6 Feb 2020 07:59:28 -0500 Received: from shards.monkeyblade.net ([23.128.96.9]:59182 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726765AbgBFM71 (ORCPT ); Thu, 6 Feb 2020 07:59:27 -0500 Received: from localhost (unknown [IPv6:2001:982:756:1:57a7:3bfd:5e85:defb]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (Client did not present a certificate) (Authenticated sender: davem-davemloft) by shards.monkeyblade.net (Postfix) with ESMTPSA id 30A2914C6027B; Thu, 6 Feb 2020 04:59:26 -0800 (PST) Date: Thu, 06 Feb 2020 13:59:24 +0100 (CET) Message-Id: <20200206.135924.1302030268583776261.davem@davemloft.net> To: cai@lca.pw Cc: kuba@kernel.org, elver@google.com, eric.dumazet@gmail.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3] skbuff: fix a data race in skb_queue_len() From: David Miller In-Reply-To: <1580841629-7102-1-git-send-email-cai@lca.pw> References: <1580841629-7102-1-git-send-email-cai@lca.pw> X-Mailer: Mew version 6.8 on Emacs 26.3 Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.5.12 (shards.monkeyblade.net [149.20.54.216]); Thu, 06 Feb 2020 04:59:27 -0800 (PST) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Qian Cai Date: Tue, 4 Feb 2020 13:40:29 -0500 > sk_buff.qlen can be accessed concurrently as noticed by KCSAN, > > BUG: KCSAN: data-race in __skb_try_recv_from_queue / unix_dgram_sendmsg > > read to 0xffff8a1b1d8a81c0 of 4 bytes by task 5371 on cpu 96: > unix_dgram_sendmsg+0x9a9/0xb70 include/linux/skbuff.h:1821 > net/unix/af_unix.c:1761 > ____sys_sendmsg+0x33e/0x370 > ___sys_sendmsg+0xa6/0xf0 > __sys_sendmsg+0x69/0xf0 > __x64_sys_sendmsg+0x51/0x70 > do_syscall_64+0x91/0xb47 > entry_SYSCALL_64_after_hwframe+0x49/0xbe > > write to 0xffff8a1b1d8a81c0 of 4 bytes by task 1 on cpu 99: > __skb_try_recv_from_queue+0x327/0x410 include/linux/skbuff.h:2029 > __skb_try_recv_datagram+0xbe/0x220 > unix_dgram_recvmsg+0xee/0x850 > ____sys_recvmsg+0x1fb/0x210 > ___sys_recvmsg+0xa2/0xf0 > __sys_recvmsg+0x66/0xf0 > __x64_sys_recvmsg+0x51/0x70 > do_syscall_64+0x91/0xb47 > entry_SYSCALL_64_after_hwframe+0x49/0xbe > > Since only the read is operating as lockless, it could introduce a logic > bug in unix_recvq_full() due to the load tearing. Fix it by adding > a lockless variant of skb_queue_len() and unix_recvq_full() where > READ_ONCE() is on the read while WRITE_ONCE() is on the write similar to > the commit d7d16a89350a ("net: add skb_queue_empty_lockless()"). > > Signed-off-by: Qian Cai Applied, thank you.