From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Cyrus-Session-Id: sloti22d1t05-667456-1519839259-2-12742711268732907679 X-Sieve: CMU Sieve 3.0 X-Spam-known-sender: no X-Spam-score: 0.0 X-Spam-hits: BAYES_00 -1.9, HEADER_FROM_DIFFERENT_DOMAINS 0.249, ME_NOAUTH 0.01, RCVD_IN_DNSWL_HI -5, T_RP_MATCHES_RCVD -0.01, LANGUAGES en, BAYES_USED global, SA_VERSION 3.4.0 X-Spam-source: IP='209.132.180.67', Host='vger.kernel.org', Country='CN', FromHeader='uk', MailFrom='org' X-Spam-charsets: plain='UTF-8' X-Resolved-to: greg@kroah.com X-Delivered-to: greg@kroah.com X-Mail-from: stable-owner@vger.kernel.org ARC-Seal: i=1; a=rsa-sha256; cv=none; d=messagingengine.com; s=arctest; t=1519839258; b=AEUXwP+cJkbFoAfnq0Ujps60DKLAEaYR6Oyj2lIzgYW+N8g BDf5i0lRRQJeVAqB64AzON76x327tnfVIdiuIE016BjaCvzaKs2/Xv7Rjyl7ShKI ymWm32S5mLnY3xUdh/dFAQxsBBgdE+rm5lNx1VVFWSiupOrYvGAmhVSie/LmyWqy ZBXmDhwrgkx5tm56jWWTwytz1yC9tphAcIv2uHIEZkU+3u/D3kFr+YXfYRqBOcTz RKgCdYVX91QO/A3QfN6l7JhIMTKRIiztaFLJQEHv17rjJACP1O5ZW1we2BjcwzOW C6YEdyedyv5SsGPhnpsaRU/6/FgbsOZewmaR2og== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=content-type:content-transfer-encoding :mime-version:from:to:cc:date:message-id:subject:in-reply-to :sender:list-id; s=arctest; t=1519839258; bh=IxIYp6iE4qNuH6tllKt oegrw3T4CPKae51cVvZlRzbc=; b=roEukWQon0I7G2IJCh3/eRQj69rAML/pjSt 2rWUuVh2XYmZ/W6HFytxjIdOowYNlGThTDmWUoCwPGFUbX8RObTXNOqoNUCpHlEC pWXe+u2i6EjkIbty3HK9lzP1HsvC5jATZlVu+9wts18IqYvZa869aXx1aGv7JS7+ IqafKAIJAJD2WUuF9od/CJcPjIs5pWJzKzsPLTwmbL8u7dltbYHU9tDaKG42akVP 2sogI3mBtlUpbLtK35feIvW0HX1Ok50juATEtG+TJqGHzY7XSLMWPKV0Pyn0E2xj Ey2JbpW9DVMeH0JWUX05karWvAmdhuAy7cIkVJ2d7yHfEx96iIA== ARC-Authentication-Results: i=1; mx3.messagingengine.com; arc=none (no signatures found); dkim=none (no signatures found); dmarc=none (p=none,has-list-id=yes,d=none) header.from=decadent.org.uk; iprev=pass policy.iprev=209.132.180.67 (vger.kernel.org); spf=none smtp.mailfrom=stable-owner@vger.kernel.org smtp.helo=vger.kernel.org; x-aligned-from=fail; x-ptr=pass x-ptr-helo=vger.kernel.org x-ptr-lookup=vger.kernel.org; x-return-mx=pass smtp.domain=vger.kernel.org smtp.result=pass smtp_org.domain=kernel.org smtp_org.result=pass smtp_is_org_domain=no header.domain=decadent.org.uk header.result=pass header_is_org_domain=yes Authentication-Results: mx3.messagingengine.com; arc=none (no signatures found); dkim=none (no signatures found); dmarc=none (p=none,has-list-id=yes,d=none) header.from=decadent.org.uk; iprev=pass policy.iprev=209.132.180.67 (vger.kernel.org); spf=none smtp.mailfrom=stable-owner@vger.kernel.org smtp.helo=vger.kernel.org; x-aligned-from=fail; x-ptr=pass x-ptr-helo=vger.kernel.org x-ptr-lookup=vger.kernel.org; x-return-mx=pass smtp.domain=vger.kernel.org smtp.result=pass smtp_org.domain=kernel.org smtp_org.result=pass smtp_is_org_domain=no header.domain=decadent.org.uk header.result=pass header_is_org_domain=yes Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933412AbeB1Rb1 (ORCPT ); Wed, 28 Feb 2018 12:31:27 -0500 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:33222 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932575AbeB1PWP (ORCPT ); Wed, 28 Feb 2018 10:22:15 -0500 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Stefano Brivio" , "Nicolai Stange" , "David S. Miller" Date: Wed, 28 Feb 2018 15:20:22 +0000 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.2 092/140] net: ipv4: emulate READ_ONCE() on ->hdrincl bit-field in raw_sendmsg() In-Reply-To: X-SA-Exim-Connect-IP: 2a02:8011:400e:2:6f00:88c8:c921:d332 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: stable-owner@vger.kernel.org X-Mailing-List: stable@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: 3.2.100-rc1 review patch. If anyone has any objections, please let me know. ------------------ 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 [bwh: Backported to 3.2: use ACCESS_ONCE()] Signed-off-by: Ben Hutchings --- net/ipv4/raw.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) --- a/net/ipv4/raw.c +++ b/net/ipv4/raw.c @@ -491,9 +491,11 @@ static int raw_sendmsg(struct kiocb *ioc 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 = ACCESS_ONCE(hdrincl); /* * Check the flags. */