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

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Date:   Tue, 23 Apr 2019 12:28:16 +0900
From:   Matteo Croce <mcroce@...hat.com>
To:     Matthew Wilcox <willy@...radead.org>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        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 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.

Thanks,
-- 
Matteo Croce
per aspera ad upstream