linux-kernel - Re: [PATCH 1/3] kernel/sysctl: support setting sysctl parameters from kernel command line

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Message-ID: <20200406140836.GA11244@42.do-not-panic.com>
Date:   Mon, 6 Apr 2020 14:08:36 +0000
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Vlastimil Babka <vbabka@...e.cz>,
        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>,
        Michal Hocko <mhocko@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        "Guilherme G . Piccoli" <gpiccoli@...onical.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Christian Brauner <christian.brauner@...ntu.com>
Subject: Re: [PATCH 1/3] kernel/sysctl: support setting sysctl parameters
 from kernel command line

On Fri, Apr 03, 2020 at 04:57:51PM -0700, Kees Cook wrote:
> On Thu, Apr 02, 2020 at 08:59:32PM +0000, Luis Chamberlain wrote:
> > We modify the copied bootparams to allow new sysctls to map to old boot params?
> 
> This strdup is so that the
> command line can have '\0's injected while it steps through the args
> (and for doing the . and / replacement).

Please ignore the const feedback then.

> > This is the least cumbersome solution I could think of. Other things
> > would require things like using qemu, etc. That seems much more messsy.
> 
> Yes. Doing an internal extension isn't testing the actual code.

But it would.

> > > This is an external interface (boot params), so
> > > I'd rather an external driver handle that testing. We don't have a
> > > common method to do that with the kernel, though.
> > 
> > Right... which begs the question now -- how do we test this sort of
> > stuff? The above would at least get us coverage while we iron something
> > more generic out for boot params.
> > 
> > > > That would test both cases with one kernel.
> > > > 
> > > > You could then also add a bogus new sysctl which also expands to a silly
> > > > raw boot param to test the wrapper you are providing. That would be the
> > > > only new test syctl you would need to add.
> > > 
> > > Sure, that seems reasonable. Supporting externally driven testing makes
> > > sense for this.
> > 
> > But again, what exactly?
> 
> I don't think anything is needed for this series. It can be boot tested
> manually.

Why test it manually when it could be tested automatically with a new kconfig?

  Luis