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=-5.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 CF707C432C0 for ; Tue, 19 Nov 2019 16:53:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A39A8223AB for ; Tue, 19 Nov 2019 16:53:39 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="QeA77eS6" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728483AbfKSQxg (ORCPT ); Tue, 19 Nov 2019 11:53:36 -0500 Received: from mail-pl1-f194.google.com ([209.85.214.194]:42741 "EHLO mail-pl1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727560AbfKSQxg (ORCPT ); Tue, 19 Nov 2019 11:53:36 -0500 Received: by mail-pl1-f194.google.com with SMTP id j12so12046233plt.9; Tue, 19 Nov 2019 08:53:36 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=subject:to:references:from:message-id:date:user-agent:mime-version :in-reply-to:content-language:content-transfer-encoding; bh=0ikEmW1Uo4O0wTwEpbsw1vK5uaPUtxj8nWEOCJAitRY=; b=QeA77eS6veKPZIsveG+jfcWwHV5debSGbGZJ1W14Wq82ggxzASoK28i/diQ7gbK4kl h9Jc04PxNHmr527ewTCO94EU/wosCb3x9UXFXudKwnLMTp/v1o3tQ+0PfIbw+EXVwdbp 33QVUIdZPTVrDePLgB8KvLgIonuH19FhjXA31t4ZxhXtiTr7BNPCN04oelDG5pgKObTM M5Toh7Q9ymkkgT6UvMoLgfC9sitLbTkDw0h78F7XvanRQtQs1Uml2zX29tQGqGA/e05d WLTNWVxl8T7tHEntbz/iYGVRKDGLGhtQqYMuU4JTTYiNMmzFBniAlZIN+sbwDtpDSsbq WsGg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=0ikEmW1Uo4O0wTwEpbsw1vK5uaPUtxj8nWEOCJAitRY=; b=dBoLqCv3zXUM2clTvqnSYaQNIVNOzMD9CPBTj7pxR4LU2mBEVWyFxFzi3BqLGbyxTm uJsoocevINa3RzHuquiLQPGLPpXO1/0LHCwXUzTQWhui7F8Tnv/E3WN5xaJC2zmez9NS WRoapJt96ewKY8LHRLONvaW0DnIztlt1CyEfCdlNMu2zIizapWBzb0CkLhpmvr0eppYA XaP7wfA6qRxKDK8U+aN33dBYO7OJdw89W16B0ksXIWQtljydPaVcF4XMe3+nZ3Vr1E5e lQKlo+C5d1WkBLiWc5W3f4TNFlEHdWXXaIBZl7VrKiQQ7ALSevzpBA9zlBg8Nf8COC+9 hKbQ== X-Gm-Message-State: APjAAAVx33wjz5hxrVILoWsBJhy3ArMv3pUx38ITINItCA6q0Od6TXse WdXVYeLGA+MkjYqPmq6fA8Y= X-Google-Smtp-Source: APXvYqygJkmb3ADs33SkUCsYqyMgEU1MYC1EWxOPKO8Eu1XEONdfouHXmzYzmNtpFSyFYX23ceHM1g== X-Received: by 2002:a17:90a:8401:: with SMTP id j1mr7728686pjn.39.1574182415755; Tue, 19 Nov 2019 08:53:35 -0800 (PST) Received: from ?IPv6:2620:15c:2c1:200:55c7:81e6:c7d8:94b? ([2620:15c:2c1:200:55c7:81e6:c7d8:94b]) by smtp.gmail.com with ESMTPSA id u65sm25969583pfb.35.2019.11.19.08.53.34 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 19 Nov 2019 08:53:34 -0800 (PST) Subject: Re: KMSAN: uninit-value in can_receive To: Oliver Hartkopp , Marc Kleine-Budde , syzbot , davem@davemloft.net, glider@google.com, linux-can@vger.kernel.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, syzkaller-bugs@googlegroups.com References: <0000000000005c08d10597a3a05d@google.com> <7934bc2b-597f-0bb3-be2d-32f3b07b4de9@hartkopp.net> <7f5c4546-0c1a-86ae-581e-0203b5fca446@pengutronix.de> <1f7d6ea7-152e-ff18-549c-b196d8b5e3a7@hartkopp.net> From: Eric Dumazet Message-ID: <9e06266a-67f3-7352-7b87-2b9144c7c9a9@gmail.com> Date: Tue, 19 Nov 2019 08:53:33 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: <1f7d6ea7-152e-ff18-549c-b196d8b5e3a7@hartkopp.net> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 11/18/19 11:35 PM, Oliver Hartkopp wrote: > > > See ioctl$ifreq https://syzkaller.appspot.com/x/log.txt?x=14563416e00000 > > 23:11:34 executing program 2: > r0 = socket(0x200000000000011, 0x3, 0x0) > ioctl$ifreq_SIOCGIFINDEX_vcan(r0, 0x8933, &(0x7f0000000040)={'vxcan1\x00', 0x0}) > bind$packet(r0, &(0x7f0000000300)={0x11, 0xc, r1}, 0x14) > sendmmsg(r0, &(0x7f0000000d00), 0x400004e, 0x0) > > We only can receive skbs from (v(x))can devices. > No matter if someone wrote to them via PF_CAN or PF_PACKET. > We check for ETH_P_CAN(FD) type and ARPHRD_CAN dev type at rx time. And what entity sets the can_skb_prv(skb)->skbcnt to zero exactly ? > >>> We additionally might think about introducing a check whether we have a >>> can_skb_reserve() created skbuff. >>> >>> But even if someone forged a skbuff without this reserved space the >>> access to can_skb_prv(skb)->skbcnt would point into some CAN frame >>> content - which is still no access to uninitialized content, right? > > So this question remains still valid whether we have a false positive from KMSAN here. I do not believe it is a false positive. It seems CAN relies on some properties of low level drivers using alloc_can_skb() or similar function. Why not simply fix this like that ? diff --git a/net/can/af_can.c b/net/can/af_can.c index 128d37a4c2e0ba5d8db69fcceec8cbd6a79380df..3e71a78d82af84caaacd0ef512b5e894efbf4852 100644 --- a/net/can/af_can.c +++ b/net/can/af_can.c @@ -647,8 +647,9 @@ static void can_receive(struct sk_buff *skb, struct net_device *dev) pkg_stats->rx_frames_delta++; /* create non-zero unique skb identifier together with *skb */ - while (!(can_skb_prv(skb)->skbcnt)) + do { can_skb_prv(skb)->skbcnt = atomic_inc_return(&skbcounter); + } while (!(can_skb_prv(skb)->skbcnt)); rcu_read_lock();