linux-kernel - Re: [PATCH] clk_register_clkdev: remove format string interface

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Message-ID: <20150904085912.GB21084@n2100.arm.linux.org.uk>
Date:	Fri, 4 Sep 2015 09:59:13 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Kees Cook <keescook@...omium.org>
Cc:	Tomeu Vizoso <tomeu@...euvizoso.net>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Michael Turquette <mturquette@...libre.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nicolas Iooss <nicolas.iooss_linux@....org>,
	linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] clk_register_clkdev: remove format string interface

On Thu, Sep 03, 2015 at 01:54:07PM -0700, Kees Cook wrote:
> Many callers either use NULL or const strings for the third argument of
> clk_register_clkdev. For those that do not and use a non-const string,
> this is a risk for format strings being accidentally processed (for
> example in device names). As this interface is already used as if it
> weren't a format string (prints nothing when NULL), and there are zero
> users of the format strings, remove the format string interface to make
> sure format strings will not leak into the clkdev.
> 
> $ git grep '\bclk_register_clkdev\b' | grep % | wc -l
> 0
> 
> Unfortunately, all the internals expect a va_list even though they treat
> a NULL format string as special. To deal with this, we must pass either
> (..., "%s", string) or (..., NULL, NULL) so that a the va_list will be
> created correctly (passing the name as an argument, not a format string).

A more clearer way to write that would be:

	if (dev_id)
		cl = clkdev_create(hw, con_id, "%s", dev_id);
	else
		cl = clkdev_create(hw, con_id, NULL);

then it's obvious what's going on.

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