linux-kernel - Re: [PATCH] sysctl: Check name array length in deprecated_sysctl

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Date:   Wed, 24 May 2017 10:07:31 -0700
From:   Kees Cook <keescook@...gle.com>
To:     Mateusz Jurczyk <mjurczyk@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Matthew Whitehead <tedheadster@...il.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sysctl: Check name array length in deprecated_sysctl_warning()

On Wed, May 24, 2017 at 5:21 AM, Mateusz Jurczyk <mjurczyk@...gle.com> wrote:
> Prevent use of uninitialized memory (originating from the stack frame of
> do_sysctl()) by verifying that the name array is filled with sufficient
> input data before comparing its specific entries with integer constants.
>
> Through timing measurement or analyzing the kernel debug logs, a user-mode
> program could potentially infer the results of comparisons against the
> uninitialized memory, and acquire some (very limited) information about the
> state of the kernel stack. The change also eliminates possible future
> warnings by tools such as KMSAN and other code checkers /
> instrumentations.
>
> Signed-off-by: Mateusz Jurczyk <mjurczyk@...gle.com>

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

-Kees

> ---
>  kernel/sysctl_binary.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/sysctl_binary.c b/kernel/sysctl_binary.c
> index ece4b177052b..38d6ba22a209 100644
> --- a/kernel/sysctl_binary.c
> +++ b/kernel/sysctl_binary.c
> @@ -1346,7 +1346,7 @@ static void deprecated_sysctl_warning(const int *name, int nlen)
>          * CTL_KERN/KERN_VERSION is used by older glibc and cannot
>          * ever go away.
>          */
> -       if (name[0] == CTL_KERN && name[1] == KERN_VERSION)
> +       if (nlen >= 2 && name[0] == CTL_KERN && name[1] == KERN_VERSION)
>                 return;
>
>         if (printk_ratelimit()) {
> --
> 2.13.0.219.gdb65acc882-goog
>



-- 
Kees Cook
Pixel Security