linux-kernel - Re: [PATCH v3] proc/sysctl: add shared variables for range check

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Date:   Tue, 30 Apr 2019 00:21:47 +0200
From:   Matteo Croce <mcroce@...hat.com>
To:     Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, linux-fsdevel@...r.kernel.org,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH v3] proc/sysctl: add shared variables for range check

On Tue, Apr 23, 2019 at 5:28 AM Matteo Croce <mcroce@...hat.com> wrote:
>
> On April 19, 2019 10:07:14 AM GMT+09:00, Matthew Wilcox <willy@...radead.org> wrote:
> > On Fri, Apr 19, 2019 at 09:17:17AM +0900, Matteo Croce wrote:
> > > > extern const int sysctl_zero;
> > > > /* comment goes here */
> > > > #define SYSCTL_ZERO ((void *)&sysctl_zero)
> > > >
> > > > and then use SYSCTL_ZERO everywhere.  That centralizes the
> > ugliness
> > > > and
> > > > makes it easier to switch over if/when extra1&2 are constified.
> > > >
> > > > But it's all a bit sad and lame :(
> > >
> > > No, we didn't decide yet. I need to check for all extra1,2
> > assignment. Not an impossible task, anyway.
> > >
> > > I agree that the casts are ugly. Your suggested macro moves the
> > ugliness in a single point, which is good. Or maybe we can do a single
> > macro like:
> > >
> > > #define SYSCTL_VAL(x) ((void *)&sysctl_##x)
> > >
> > > to avoid defining one for every value. And when we decide that
> > everything can be const, we just update the macro.
> >
> > If we're going to do that, we can save two EXPORTs and do:
> >
> > const int sysctl_vals[] = { 0, 1, -1 };
> > EXPORT_SYMBOL(sysctl_vals);
> >
> > #define SYSCTL_ZERO   ((void *)&sysctl_vals[0])
>
> Hi Matthew,
>
> I like this approach, regardless of the const or not const extra1.
>
> I'll be AFK for a few days, then I will investigate if extra1,2 can be made const and then prepare a v4 with the single export.

Hi all,

I turned extra{1,2) to const and I see no issues.
I'm sending a v4 with extra{1,2} const, a single export for all vars
as suggested by Matthew, and the define suggested by Andrew.
Comments are welcome as usual.

Regards,
--
Matteo Croce
per aspera ad upstream