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=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED 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 CD537C04EBD for ; Tue, 16 Oct 2018 15:34:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 980ED208E4 for ; Tue, 16 Oct 2018 15:34:14 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 980ED208E4 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727208AbeJPXZL (ORCPT ); Tue, 16 Oct 2018 19:25:11 -0400 Received: from mx1.redhat.com ([209.132.183.28]:40854 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727075AbeJPXZL (ORCPT ); Tue, 16 Oct 2018 19:25:11 -0400 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 6CF0A88E4F; Tue, 16 Oct 2018 15:34:11 +0000 (UTC) Received: from llong.remote.csb (dhcp-17-8.bos.redhat.com [10.18.17.8]) by smtp.corp.redhat.com (Postfix) with ESMTP id 2DACB7A7B2; Tue, 16 Oct 2018 15:34:08 +0000 (UTC) Subject: Re: [PATCH v1 2/2] sysctl: handle overflow for file-max To: Christian Brauner Cc: keescook@chromium.org, linux-kernel@vger.kernel.org, ebiederm@xmission.com, mcgrof@kernel.org, akpm@linux-foundation.org, joe.lawrence@redhat.com, linux@dominikbrodowski.net, viro@zeniv.linux.org.uk References: <20181015105544.4395-1-christian@brauner.io> <20181015105544.4395-3-christian@brauner.io> <22319ca1-6dab-fe36-40d5-9c88f7a175ee@redhat.com> <20181016152100.zg2pmyk6puc5qsr5@brauner.io> <11e172de-0953-2c46-c0f0-72c42ae9a910@redhat.com> <20181016152955.vcjtzcx5rzlxeovh@brauner.io> From: Waiman Long Organization: Red Hat Message-ID: <4aa6ff1a-28c7-db85-1fea-fa0e4fc1ef2e@redhat.com> Date: Tue, 16 Oct 2018 11:34:07 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.0 MIME-Version: 1.0 In-Reply-To: <20181016152955.vcjtzcx5rzlxeovh@brauner.io> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.25]); Tue, 16 Oct 2018 15:34:11 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/16/2018 11:29 AM, Christian Brauner wrote: > On Tue, Oct 16, 2018 at 11:25:42AM -0400, Waiman Long wrote: >> On 10/16/2018 11:21 AM, Christian Brauner wrote: >>> On Tue, Oct 16, 2018 at 11:13:28AM -0400, Waiman Long wrote: >>>> On 10/15/2018 06:55 AM, Christian Brauner wrote: >>>>> Currently, when writing >>>>> >>>>> echo 18446744073709551616 > /proc/sys/fs/file-max >>>>> >>>>> /proc/sys/fs/file-max will overflow and be set to 0. That quickly >>>>> crashes the system. >>>>> This commit explicitly caps the value for file-max to ULONG_MAX. >>>>> >>>>> Note, this isn't technically necessary since proc_get_long() will already >>>>> return ULONG_MAX. However, two reason why we still should do this: >>>>> 1. it makes it explicit what the upper bound of file-max is instead of >>>>> making readers of the code infer it from proc_get_long() themselves >>>>> 2. other tunebles than file-max may want to set a lower max value than >>>>> ULONG_MAX and we need to enable __do_proc_doulongvec_minmax() to handle >>>>> such cases too >>>>> >>>>> Cc: Kees Cook >>>>> Signed-off-by: Christian Brauner >>>>> --- >>>>> v0->v1: >>>>> - if max value is < than ULONG_MAX use max as upper bound >>>>> - (Dominik) remove double "the" from commit message >>>>> --- >>>>> kernel/sysctl.c | 4 ++++ >>>>> 1 file changed, 4 insertions(+) >>>>> >>>>> diff --git a/kernel/sysctl.c b/kernel/sysctl.c >>>>> index 97551eb42946..226d4eaf4b0e 100644 >>>>> --- a/kernel/sysctl.c >>>>> +++ b/kernel/sysctl.c >>>>> @@ -127,6 +127,7 @@ static int __maybe_unused one = 1; >>>>> static int __maybe_unused two = 2; >>>>> static int __maybe_unused four = 4; >>>>> static unsigned long one_ul = 1; >>>>> +static unsigned long ulong_max = ULONG_MAX; >>>>> static int one_hundred = 100; >>>>> static int one_thousand = 1000; >>>>> #ifdef CONFIG_PRINTK >>>>> @@ -1696,6 +1697,7 @@ static struct ctl_table fs_table[] = { >>>>> .maxlen = sizeof(files_stat.max_files), >>>>> .mode = 0644, >>>>> .proc_handler = proc_doulongvec_minmax, >>>>> + .extra2 = &ulong_max, >>>> What is the point of having a maximum value of ULONG_MAX anyway? No >>>> value you can put into a ulong type can be bigger than that. >>> This is changed in the new code to LONG_MAX. See the full thread for >>> context. There's also an additional explantion in the commit message. >>> >>>>> }, >>>>> { >>>>> .procname = "nr_open", >>>>> @@ -2795,6 +2797,8 @@ static int __do_proc_doulongvec_minmax(void *data, struct ctl_table *table, int >>>>> break; >>>>> if (neg) >>>>> continue; >>>>> + if (max && val > *max) >>>>> + val = *max; >>>>> val = convmul * val / convdiv; >>>>> if ((min && val < *min) || (max && val > *max)) >>>>> continue; >>>> This does introduce a change in behavior. Previously the out-of-bound >>>> value is ignored, now it is capped at its maximum. This is a >>>> user-visible change. >>> Not completely true though. Try >>> >>> echo 18446744073709551616 > /proc/sys/fs/file-max >>> >>> on a system you find acceptable loosing. >>> So this is an acceptable user-visible change I'd say. But I'm open to >>> other suggestions. >> I am not saying this is unacceptable. I just say this is a user-visible >> change and so should be documented somehow. BTW, you cap the max value, > Sure, I'll update linux manpages and I can CC stable on the next round. > >> but not the min value. So there is inconsistency. I would say you either >> do both, or none of them. > The min value is 0. I don't think it needs to be set explicitly. I just > kept the max value because it is != ULONG_MAX but LONG_MAX for file-max. I think you are making the change with just one use case in mind. This is a generic function that can be used by many different callers. So any change you make has to be applicable to all use cases. You just can't assume min is always 0 in all the other use cases. Cheers, Longman