linux-kernel - Re: [PATCH] doc: update 'unique identifiers'

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Message-ID: <CAGXu5jKKojS4SjHwwxKKeU=5HCBuv_iFROHC+r3jb9D4BY4U0w@mail.gmail.com>
Date:   Mon, 4 Dec 2017 13:28:45 -0800
From:   Kees Cook <keescook@...omium.org>
To:     "Tobin C. Harding" <me@...in.cc>
Cc:     Jonathan Corbet <corbet@....net>,
        Laura Abbott <labbott@...hat.com>,
        Jessica Yu <jeyu@...hat.com>, linux-doc@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] doc: update 'unique identifiers'

On Mon, Dec 4, 2017 at 1:22 PM, Tobin C. Harding <me@...in.cc> wrote:
> Advice about what to use as a unique identifier is no longer valid since
> patch series was merged to hash pointers printed with %p. We can use
> this as a unique identifier now.
>
> Signed-off-by: Tobin C. Harding <me@...in.cc>

I don't agree: %p should still not be encouraged. Exposing an
identifier to userspace needs careful consideration, and atomics,
idrs, etc, continue to be a good recommendation here, as far as I'm
concerned.

-Kees

> ---
>  Documentation/security/self-protection.rst | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/security/self-protection.rst b/Documentation/security/self-protection.rst
> index 60c8bd8b77bf..f10f47cad825 100644
> --- a/Documentation/security/self-protection.rst
> +++ b/Documentation/security/self-protection.rst
> @@ -274,8 +274,8 @@ Unique identifiers
>  ------------------
>
>  Kernel memory addresses must never be used as identifiers exposed to
> -userspace. Instead, use an atomic counter, an idr, or similar unique
> -identifier.
> +userspace. Printk specifier %p hashes addresses by default now and can be
> +used as a unique identifier.
>
>  Memory initialization
>  ---------------------
> --
> 2.7.4
>



-- 
Kees Cook
Pixel Security