linux-kernel - Re: [RFC v2 1/2] kernel/sysctl: support setting sysctl parameters from kernel command line

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Message-ID: <202003260018.81648AA67@keescook>
Date:   Thu, 26 Mar 2020 00:21:30 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Iurii Zaikin <yzaikin@...gle.com>,
        linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        linux-mm@...ck.org, Ivan Teterevkov <ivan.teterevkov@...anix.com>,
        David Rientjes <rientjes@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        "Guilherme G . Piccoli" <gpiccoli@...onical.com>
Subject: Re: [RFC v2 1/2] kernel/sysctl: support setting sysctl parameters
 from kernel command line

On Thu, Mar 26, 2020 at 07:58:29AM +0100, Michal Hocko wrote:
> On Wed 25-03-20 17:20:40, Eric W. Biederman wrote:
> > Vlastimil Babka <vbabka@...e.cz> writes:
> [...]
> > > +	if (strncmp(param, "sysctl.", sizeof("sysctl.") - 1))
> > > +		return 0;
> > 
> > Is there any way we can use a slash separated path.  I know
> > in practice there are not any sysctl names that don't have
> > a '.' in them but why should we artifically limit ourselves?
> 
> Because this is the normal userspace interface? Why should it be any
> different from calling sysctl?

Right. The common method from userspace is dot-separated (which I agree
is weird, but it's been like this for ages: see manpages sysctl(8) and
sysctl.conf(5) for the details and examples). While "/" is accepted by
sysctl, the files shipped in /etc/sysctl.d/ are all using "."  separators.

-- 
Kees Cook