linux-kernel - Re: [PATCH v3 0/2] sysctl: handle overflow for file-max

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Message-ID: <CAGXu5jJwSRQ3dOgNW_X0Fk+8gT+ACiBZPJ79g-aCfqiWsm=ewg@mail.gmail.com>
Date:   Mon, 29 Oct 2018 14:44:29 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Christian Brauner <christian@...uner.io>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Waiman Long <longman@...hat.com>,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        Al Viro <viro@...iv.linux.org.uk>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH v3 0/2] sysctl: handle overflow for file-max

On Mon, Oct 29, 2018 at 7:58 AM, Christian Brauner <christian@...uner.io> wrote:
> On Wed, Oct 17, 2018 at 12:33:20AM +0200, Christian Brauner wrote:
>> Hey,
>>
>> Here is v3 of this patchset. Changelogs are in the individual commits.
>>
>> 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.
>>
>> The first version of this patch intended to detect the overflow and cap
>> at ULONG_MAX. However, we should not do this and rather return EINVAL on
>> overflow. The reasons are:
>> - this aligns with other sysctl handlers that simply reject overflows
>>   (cf. [1], [2], and a bunch of others)
>> - we already do a partial fail on overflow right now
>>   Namely, when the TMPBUFLEN is exceeded. So we already reject values
>>   such as 184467440737095516160 (21 chars) but accept values such as
>>   18446744073709551616 (20 chars) but both are overflows. So we should
>>   just always reject 64bit overflows and not special-case this based on
>>   the number of chars.
>>
>> (This patchset is in reference to https://lkml.org/lkml/2018/10/11/585.)
>
> Just so that we don't forget, can we make sure that this gets picked
> into linux-next? :)

I was hoping akpm would take this? Andrew, does the v3 look okay to you?

-Kees

-- 
Kees Cook