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

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Date:   Tue, 16 Apr 2019 22:21:16 -0500
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>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Alexey Dobriyan <adobriyan@...il.com>
Subject: Re: [PATCH 2/2] kernel: use sysctl shared variables for range check

On Mon, Apr 8, 2019 at 5:09 PM Matteo Croce <mcroce@...hat.com> wrote:
>
> Use the shared variables for range check, instead of declaring a local one
> in every source file.
>
> Signed-off-by: Matteo Croce <mcroce@...hat.com>
> ---
>  kernel/pid_namespace.c |   3 +-
>  kernel/sysctl.c        | 193 ++++++++++++++++++++---------------------
>  kernel/ucount.c        |   6 +-
>  3 files changed, 98 insertions(+), 104 deletions(-)
>
> diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
> index aa6e72fb7c08..ddbb51bc4968 100644
> --- a/kernel/pid_namespace.c
> +++ b/kernel/pid_namespace.c
> @@ -290,14 +290,13 @@ static int pid_ns_ctl_handler(struct ctl_table *table, int write,
>  }
>
>  extern int pid_max;
> -static int zero = 0;
>  static struct ctl_table pid_ns_ctl_table[] = {
>         {
>                 .procname = "ns_last_pid",
>                 .maxlen = sizeof(int),
>                 .mode = 0666, /* permissions are checked in the handler */
>                 .proc_handler = pid_ns_ctl_handler,
> -               .extra1 = &zero,
> +               .extra1 = (void *)&sysctl_zero,

BTW, I don't think these (void *) casts are actually needed. I thought
extra1/2 were already void * so assignments don't need the casting.

-- 
Kees Cook