linux-kernel - Re: [GIT PULL] more printk for 6.15

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Message-ID: <202504030913.B50F046CB7@keescook>
Date: Thu, 3 Apr 2025 09:14:54 -0700
From: Kees Cook <kees@...nel.org>
To: Andy Shevchenko <andy.shevchenko@...il.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
	Nathan Chancellor <nathan@...nel.org>,
	Petr Mladek <pmladek@...e.com>,
	Sergey Senozhatsky <senozhatsky@...omium.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	John Ogness <john.ogness@...utronix.de>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Peter Zijlstra <peterz@...radead.org>, linux-kernel@...r.kernel.org
Subject: Re: [GIT PULL] more printk for 6.15

On Wed, Apr 02, 2025 at 10:25:46PM +0300, Andy Shevchenko wrote:
> I actually don't know what the benefit of __printf() attribute from
> security (?) point of view is. I may speculate that this helps to
> validate the format string and arguments (when provided as ...) and
> helps with potential wrong argument sizes, etc. Kees, what do you
> think about Linus' proposal?

It's a bit low on the severity list since we long ago removed %n, but
it's effectively a form of type-checking for arguments to printf. I look
at it more as a robustness/correctness checker. If we can make it work,
it's good to have. And it looks like Nathan's suggestion will make it
feasible.

-Kees

-- 
Kees Cook