linux-kernel - Re: [RFC][PATCH] printf: Harden accessing pointer dereference in vsprintf()

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Message-ID: <202501061632.76CF72FC@keescook>
Date: Mon, 6 Jan 2025 16:33:00 -0800
From: Kees Cook <kees@...nel.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Petr Mladek <pmladek@...e.com>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: Re: [RFC][PATCH] printf: Harden accessing pointer dereference in
 vsprintf()

On Mon, Jan 06, 2025 at 05:27:22PM -0500, Steven Rostedt wrote:
> From: Steven Rostedt <rostedt@...dmis.org>
> 
> For extra safety from crashing the kernel, add a
> copy_from_kernel_nofault() in check_pointer_msg(). If it fails to read the
> memory, then return "(efault)".
> 
> This isn't full proof, as the length of the pointer being read could
> possibly go into bad memory, but this should catch the majority of errors.
> 
> Linus had suggested adding this kind of check[1]. This is a bit different
> than Linus's solution as it utilizes copy_from_kernel_nofault() and doesn't
> require calls to pagefault_disable() and extra labels.
> 
> [1] https://lore.kernel.org/all/CAHk-=wh3cUC2a=yJv42HTjDLCp6VM+GTky+q65vV_Q33BeoxAg@mail.gmail.com/
> 
> Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>

Seems reasonable to me.

Reviewed-by: Kees Cook <kees@...nel.org>

-Kees

-- 
Kees Cook