linux-kernel - Re: [PATCH v5] proc/sysctl: add shared variables for range check

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Message-ID: <CAGXu5jJG1D6YvTaSY3hpB8_APmwe=rGn8FkyAfCGuQZ3O2j1Yg@mail.gmail.com>
Date:   Tue, 30 Apr 2019 11:14:20 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Matteo Croce <mcroce@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH v5] proc/sysctl: add shared variables for range check

On Tue, Apr 30, 2019 at 11:01 AM Matteo Croce <mcroce@...hat.com> wrote:
>
> In the sysctl code the proc_dointvec_minmax() function is often used to
> validate the user supplied value between an allowed range. This function
> uses the extra1 and extra2 members from struct ctl_table as minimum and
> maximum allowed value.
>
> On sysctl handler declaration, in every source file there are some readonly
> variables containing just an integer which address is assigned to the
> extra1 and extra2 members, so the sysctl range is enforced.
>
> The special values 0, 1 and INT_MAX are very often used as range boundary,
> leading duplication of variables like zero=0, one=1, int_max=INT_MAX in
> different source files:
>
>     $ git grep -E '\.extra[12].*&(zero|one|int_max)\b' |wc -l
>     248
>
> Add a const int array containing the most commonly used values,
> some macros to refer more easily to the correct array member,
> and use them instead of creating a local one for every object file.
>
> This is the bloat-o-meter output comparing the old and new binary
> compiled with the default Fedora config:
>
>     # scripts/bloat-o-meter -d vmlinux.o.old vmlinux.o
>     add/remove: 2/2 grow/shrink: 0/2 up/down: 24/-188 (-164)
>     Data                                         old     new   delta
>     sysctl_vals                                    -      12     +12
>     __kstrtab_sysctl_vals                          -      12     +12
>     max                                           14      10      -4
>     int_max                                       16       -     -16
>     one                                           68       -     -68
>     zero                                         128      28    -100
>     Total: Before=20583249, After=20583085, chg -0.00%
>
> Signed-off-by: Matteo Croce <mcroce@...hat.com>

Acked-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook