linux-kernel - Re: [PATCH 3/3] vsprintf: ignore %n again

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Date:	Tue, 8 Oct 2013 13:28:45 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Kees Cook <keescook@...omium.org>
Cc:	linux-kernel@...r.kernel.org,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	joe@...ches.com
Subject: Re: [PATCH 3/3] vsprintf: ignore %n again

On Mon,  7 Oct 2013 19:56:51 -0700 Kees Cook <keescook@...omium.org> wrote:

> This ignores %n in printf again, as was originally documented. Implementing
> %n poses a greater security risk than utility, so it should stay ignored.
> To help anyone attempting to use %n, a warning will be emitted if it is
> encountered.
> 
> Based on earlier patch by Joe Perches.

Well this sucks.  Nowhere in this patchset are we told what is the
alleged security risk with %n.  There's even a runtime warning telling
people not to use it, but we've provided no way for them to find out
*why*.

Please send along suitable changelog text so I can fix this up.

A new checkpatch rule might be appropriate?

Two of these patches were acked-by:you.  But you sent the patches, so I
changed these to Signed-off-by:, as per
Documentation/SubmittingPatches, section 12.

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