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

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Date:   Wed, 4 Mar 2020 22:47:18 -0800
From:   Kees Cook <keescook@...omium.org>
To:     James Troup <james.troup@...onical.com>
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

Ah! A wild Troup appears! :)

On Thu, Mar 05, 2020 at 07:22:31AM +0100, James Troup wrote:
> 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?

Yeah, good point; that should be more clear.

> 
> > +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/ ?

I'll rewrite this whole area...

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

Thanks for the review! I wonder why ":set spell" missed that...

-Kees

-- 
Kees Cook