Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932916AbeAHNB1 (ORCPT + 1 other); Mon, 8 Jan 2018 08:01:27 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:43716 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932900AbeAHNBY (ORCPT ); Mon, 8 Jan 2018 08:01:24 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, TSUKADA Koutaro , Oleg Nesterov , Al Viro , Andrew Morton , Linus Torvalds Subject: [PATCH 4.14 08/38] kernel/acct.c: fix the acct->needcheck check in check_free_space() Date: Mon, 8 Jan 2018 13:59:01 +0100 Message-Id: <20180108125916.481848139@linuxfoundation.org> X-Mailer: git-send-email 2.15.1 In-Reply-To: <20180108125915.951963528@linuxfoundation.org> References: <20180108125915.951963528@linuxfoundation.org> User-Agent: quilt/0.65 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: 4.14-stable review patch. If anyone has any objections, please let me know. ------------------ From: Oleg Nesterov commit 4d9570158b6260f449e317a5f9ed030c2504a615 upstream. As Tsukada explains, the time_is_before_jiffies(acct->needcheck) check is very wrong, we need time_is_after_jiffies() to make sys_acct() work. Ignoring the overflows, the code should "goto out" if needcheck > jiffies, while currently it checks "needcheck < jiffies" and thus in the likely case check_free_space() does nothing until jiffies overflow. In particular this means that sys_acct() is simply broken, acct_on() sets acct->needcheck = jiffies and expects that check_free_space() should set acct->active = 1 after the free-space check, but this won't happen if jiffies increments in between. This was broken by commit 32dc73086015 ("get rid of timer in kern/acct.c") in 2011, then another (correct) commit 795a2f22a8ea ("acct() should honour the limits from the very beginning") made the problem more visible. Link: http://lkml.kernel.org/r/20171213133940.GA6554@redhat.com Fixes: 32dc73086015 ("get rid of timer in kern/acct.c") Reported-by: TSUKADA Koutaro Suggested-by: TSUKADA Koutaro Signed-off-by: Oleg Nesterov Cc: Al Viro Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- kernel/acct.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/kernel/acct.c +++ b/kernel/acct.c @@ -102,7 +102,7 @@ static int check_free_space(struct bsd_a { struct kstatfs sbuf; - if (time_is_before_jiffies(acct->needcheck)) + if (time_is_after_jiffies(acct->needcheck)) goto out; /* May block */