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

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Date:   Sun, 9 Dec 2018 17:40:09 +0100
From:   Christian Brauner <christian.brauner@...onical.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Christian Brauner <christian@...uner.io>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>, mcgrof@...nel.org,
        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 10:44 PM Kees Cook <keescook@...omium.org> wrote:
>
> 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?

gentle ping again :)

Christian