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=ham 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 86115C4332B for ; Thu, 19 Mar 2020 13:17:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4D3652098B for ; Thu, 19 Mar 2020 13:17:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1584623824; bh=QxtaDxcfQEQ1UKz0PJyRYKh2BCVbPnsBm3vuLhOG/lI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=Y0GNUXQgVp9dWhqQ9FmeeyroPWR1okmuBbcqOc2w7ktBRz9QlAskl373MqqaY2ZuS 91WJutVNaVjp5vzXuJoJzGW5Au0jYt/amlwlDuklpFOWCjGwkoYE1Wo1EeE5xTGnAZ AI+bdpA0xtfaEQc1l1gpWTi85f9THqPJ1sfh4dx0= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729381AbgCSNRD (ORCPT ); Thu, 19 Mar 2020 09:17:03 -0400 Received: from mail.kernel.org ([198.145.29.99]:37886 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728587AbgCSNQ7 (ORCPT ); Thu, 19 Mar 2020 09:16:59 -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 04C952098B; Thu, 19 Mar 2020 13:16:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1584623819; bh=QxtaDxcfQEQ1UKz0PJyRYKh2BCVbPnsBm3vuLhOG/lI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=AL0twPKEWbf454bozPApl9kC4TKPTJlI03qfrZSRCvrKvGJ+rz8OoB4wKoVT5+bWP a6lEa/iNrKDX6shrxnhE2vqcLg3p1PY3IODCOSsTV1ezgOuMqrLZegdz0Q4IGSEf9u ToXW1VAF1EXAAtw9g3T0mRA9k1X9v7J5acu+zUu8= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Vasily Averin , Tejun Heo Subject: [PATCH 4.14 37/99] cgroup: cgroup_procs_next should increase position index Date: Thu, 19 Mar 2020 14:03:15 +0100 Message-Id: <20200319123953.062335196@linuxfoundation.org> X-Mailer: git-send-email 2.25.2 In-Reply-To: <20200319123941.630731708@linuxfoundation.org> References: <20200319123941.630731708@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Vasily Averin commit 2d4ecb030dcc90fb725ecbfc82ce5d6c37906e0e upstream. If seq_file .next fuction does not change position index, read after some lseek can generate unexpected output: 1) dd bs=1 skip output of each 2nd elements $ dd if=/sys/fs/cgroup/cgroup.procs bs=8 count=1 2 3 4 5 1+0 records in 1+0 records out 8 bytes copied, 0,000267297 s, 29,9 kB/s [test@localhost ~]$ dd if=/sys/fs/cgroup/cgroup.procs bs=1 count=8 2 4 <<< NB! 3 was skipped 6 <<< ... and 5 too 8 <<< ... and 7 8+0 records in 8+0 records out 8 bytes copied, 5,2123e-05 s, 153 kB/s This happen because __cgroup_procs_start() makes an extra extra cgroup_procs_next() call 2) read after lseek beyond end of file generates whole last line. 3) read after lseek into middle of last line generates expected rest of last line and unexpected whole line once again. Additionally patch removes an extra position index changes in __cgroup_procs_start() Cc: stable@vger.kernel.org https://bugzilla.kernel.org/show_bug.cgi?id=206283 Signed-off-by: Vasily Averin Signed-off-by: Tejun Heo Signed-off-by: Greg Kroah-Hartman --- kernel/cgroup/cgroup.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -4249,6 +4249,9 @@ static void *cgroup_procs_next(struct se struct kernfs_open_file *of = s->private; struct css_task_iter *it = of->priv; + if (pos) + (*pos)++; + return css_task_iter_next(it); } @@ -4264,7 +4267,7 @@ static void *__cgroup_procs_start(struct * from position 0, so we can simply keep iterating on !0 *pos. */ if (!it) { - if (WARN_ON_ONCE((*pos)++)) + if (WARN_ON_ONCE((*pos))) return ERR_PTR(-EINVAL); it = kzalloc(sizeof(*it), GFP_KERNEL); @@ -4272,10 +4275,11 @@ static void *__cgroup_procs_start(struct return ERR_PTR(-ENOMEM); of->priv = it; css_task_iter_start(&cgrp->self, iter_flags, it); - } else if (!(*pos)++) { + } else if (!(*pos)) { css_task_iter_end(it); css_task_iter_start(&cgrp->self, iter_flags, it); - } + } else + return it->cur_task; return cgroup_procs_next(s, NULL, NULL); }