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=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 B8E7CC47254 for ; Fri, 1 May 2020 14:01:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8FE5C2051A for ; Fri, 1 May 2020 14:01:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588341717; bh=MPS1oniKcLpHTYJf5xEFeeb2N3GF+OU8Rj9Q5VoItQs=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=l6gmdt+/bQSlKOv6BgPSQ1KDCiPPI0uLN2Fo0vR73cBD/V4j9VxyKReKS9w9+v1R7 uBSvykkMM1K7rXEpCLXdt73KJx5qNgee8r4cCIGjLKHCpza+BFOXZpjwH/V9RJ0LLn 7K1DLcBuasItLIC2QsQWVXzoCXoS9Z8dHjuj1MpA= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728907AbgEANY7 (ORCPT ); Fri, 1 May 2020 09:24:59 -0400 Received: from mail.kernel.org ([198.145.29.99]:45566 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728919AbgEANY5 (ORCPT ); Fri, 1 May 2020 09:24:57 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (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 109AF216FD; Fri, 1 May 2020 13:24:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588339497; bh=MPS1oniKcLpHTYJf5xEFeeb2N3GF+OU8Rj9Q5VoItQs=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=VyXJPc81rVXSBvHjpCI0D+BNxjdavELG7YrC+G0Iedl51HRgqQZRdfT2bfTzfnJk9 AX60wBoip3m50JGmDPkyRHKdqI10bvXemvR/oX9Zx+9ZA0d7creT3PxBLoA57DCLGY 8TjAnsGE4azQ99q627o0iUCcFks9TUDjzasdCloQ= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Nicolai Stange , Stefano Brivio , "David S. Miller" , Guenter Roeck Subject: [PATCH 4.4 03/70] net: ipv4: emulate READ_ONCE() on ->hdrincl bit-field in raw_sendmsg() Date: Fri, 1 May 2020 15:20:51 +0200 Message-Id: <20200501131514.209892874@linuxfoundation.org> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20200501131513.302599262@linuxfoundation.org> References: <20200501131513.302599262@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Nicolai Stange commit 20b50d79974ea3192e8c3ab7faf4e536e5f14d8f upstream. Commit 8f659a03a0ba ("net: ipv4: fix for a race condition in raw_sendmsg") fixed the issue of possibly inconsistent ->hdrincl handling due to concurrent updates by reading this bit-field member into a local variable and using the thus stabilized value in subsequent tests. However, aforementioned commit also adds the (correct) comment that /* hdrincl should be READ_ONCE(inet->hdrincl) * but READ_ONCE() doesn't work with bit fields */ because as it stands, the compiler is free to shortcut or even eliminate the local variable at its will. Note that I have not seen anything like this happening in reality and thus, the concern is a theoretical one. However, in order to be on the safe side, emulate a READ_ONCE() on the bit-field by doing it on the local 'hdrincl' variable itself: int hdrincl = inet->hdrincl; hdrincl = READ_ONCE(hdrincl); This breaks the chain in the sense that the compiler is not allowed to replace subsequent reads from hdrincl with reloads from inet->hdrincl. Fixes: 8f659a03a0ba ("net: ipv4: fix for a race condition in raw_sendmsg") Signed-off-by: Nicolai Stange Reviewed-by: Stefano Brivio Signed-off-by: David S. Miller Cc: Guenter Roeck Signed-off-by: Greg Kroah-Hartman --- net/ipv4/raw.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) --- a/net/ipv4/raw.c +++ b/net/ipv4/raw.c @@ -507,9 +507,11 @@ static int raw_sendmsg(struct sock *sk, goto out; /* hdrincl should be READ_ONCE(inet->hdrincl) - * but READ_ONCE() doesn't work with bit fields + * but READ_ONCE() doesn't work with bit fields. + * Doing this indirectly yields the same result. */ hdrincl = inet->hdrincl; + hdrincl = READ_ONCE(hdrincl); /* * Check the flags. */