From patchwork Tue Mar 17 10:54:55 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg KH X-Patchwork-Id: 229355 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,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 133B3C3F2CE for ; Tue, 17 Mar 2020 10:58:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DA90820735 for ; Tue, 17 Mar 2020 10:58:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1584442687; bh=1gX4O/L3WbZgkcCLkjDlA5gGibw+XJYIraZw8YLJn8U=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=q4p4C4ajANWl7pQc7fBmqJ0JDwfaPFMkWp7X6lpz/EmVWEWOatP/J3n5qFJX8N0ZX KKm6vylIOtxttFipL3AtGNOEd650YA65UL3eek5CR2CYs2QBTWO5ZfGGfmEQz+cP6/ C03SdkpGIvm/qvY7AYFd5XvXJJCYXuEl81JQPCxQ= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727141AbgCQK6D (ORCPT ); Tue, 17 Mar 2020 06:58:03 -0400 Received: from mail.kernel.org ([198.145.29.99]:36022 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726683AbgCQK6A (ORCPT ); Tue, 17 Mar 2020 06:58:00 -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 6F63120714; Tue, 17 Mar 2020 10:57:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1584442679; bh=1gX4O/L3WbZgkcCLkjDlA5gGibw+XJYIraZw8YLJn8U=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=VEhGLTCE3LRCpBSd/eE0VET3C1+/++NJUD9/EH0LWhRGBiCEgP0BCUO0DGTLGy5Bj hSGxuZ5R6HM/wiJ1+sRtEprftNFhKMckaZe/R2doQgAw5ApMUToaBIJAymG/GspXkZ 2jtjjQqmAVVISRqmOcz5265bGOFqz4GHqYhcGojQ= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Vasily Averin , Tejun Heo Subject: [PATCH 4.19 46/89] cgroup: cgroup_procs_next should increase position index Date: Tue, 17 Mar 2020 11:54:55 +0100 Message-Id: <20200317103305.250175275@linuxfoundation.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20200317103259.744774526@linuxfoundation.org> References: <20200317103259.744774526@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@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 @@ -4355,6 +4355,9 @@ 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); } @@ -4370,7 +4373,7 @@ 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); @@ -4378,10 +4381,11 @@ 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); }