linux-kernel - Re: [PATCH 2/2] kernel: use sysctl shared variables for range check

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Date:   Wed, 10 Apr 2019 21:23:54 +0200
From:   Matteo Croce <mcroce@...hat.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Alexey Dobriyan <adobriyan@...il.com>
Subject: Re: [PATCH 2/2] kernel: use sysctl shared variables for range check

On Wed, Apr 10, 2019 at 8:46 PM Kees Cook <keescook@...omium.org> wrote:
>
> On Mon, Apr 8, 2019 at 3:09 PM Matteo Croce <mcroce@...hat.com> wrote:
> >
> > Use the shared variables for range check, instead of declaring a local one
> > in every source file.
>
> I was expecting this to be a tree-wide change for all the cases found
> by patch 1's "git grep".
>

Hi Kees,

I have already the whole patch ready, but I was frightened by the
output of get_maintainer.pl, so I decided to split the patch into
small pieces and send the first one.
Patches for /proc/sys/net and drivers/ are pretty big, and can be
merged after the 1/2 inclusion.

> Slight change to the grep for higher accuracy:
>
> $ git grep -E '\.extra[12].*&(zero|one|int_max)\b' |wc -l
> 245
>

Right, my regexp wrongly matches also one_hundred, one_jiffy, etc.
Anywqay, I did the changes by hand, so apart the commit message, the
content should be safe.

> Only 31 sources:
> $ git grep -E '\.extra[12].*&(zero|one|int_max)\b' | cut -d: -f1 |
> sort -u > /tmp/list.txt
> $ wc -l /tmp/list.txt
> 31
>
> One thing I wonder about is if any of these cases depend on the extra
> variable being non-const (many of these are just "static int").
>
> $ egrep -H '\b(zero|one|int_max)\b.*=' $(cat /tmp/list.txt) | grep -v static
>
> Looks like none, so it'd be safe. How about doing this tree-wide for
> all 31 cases? (Coccinelle might be able to help.)
>

It could be true for other sysctl values like
xpc_disengage_max_timelimit or fscache_op_wq, but it's very unlikely
that someone writes, for example, 5 into a variable named "zero". If
it does, it most likely a bug, so const is our friend.

Regards,
-- 
Matteo Croce
per aspera ad upstream