linux-kernel - Re: [PATCH] docs: deprecated.rst: Add %p to the list

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Message-ID: <87mu8vtj6g.fsf@canonical.com>
Date:   Thu, 05 Mar 2020 07:22:31 +0100
From:   James Troup <james.troup@...onical.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Jonathan Corbet <corbet@....net>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] docs: deprecated.rst: Add %p to the list

Kees Cook <keescook@...omium.org> writes:

> diff --git a/Documentation/process/deprecated.rst b/Documentation/process/deprecated.rst
> index f9f196d3a69b..a4db119f4e09 100644
> --- a/Documentation/process/deprecated.rst
> +++ b/Documentation/process/deprecated.rst
> @@ -109,6 +109,23 @@ the given limit of bytes to copy. This is inefficient and can lead to
>  linear read overflows if a source string is not NUL-terminated. The
>  safe replacement is :c:func:`strscpy`.
>  
> +%p format specifier
> +-------------------
> +Using %p in format strings leads to a huge number of address exposures.

Perhaps this sentence should be in the past tense, since %p currently
prints a hashed value?

> +Instead of leaving these to be exploitable, "%p" should not be used in
> +the kernel.

On its face, this seems to contradict the guidance below?

> If used currently, it is a hashed value, rendering it

Perhaps: s/it is/it prints/ ?

> +unusable for addressing. Paraphrasing Linus's current `guideance
> <https://lore.kernel.org/lkml/CA+55aFwQEd_d40g4mUCSsVRZzrFPUJt74vc6PPpb675hYNXcKw@mail.gmail.com/>`_:

Typo: guidance

> +- Just use %p and get the hashed value.

-- 
James