linux-kernel - Re: [PATCH] clk_register_clkdev: handle callers needing format string

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Date:	Fri, 31 Jul 2015 12:03:18 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Tomeu Vizoso <tomeu@...euvizoso.net>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-clk@...r.kernel.org
Subject: Re: [PATCH] clk_register_clkdev: handle callers needing format string

On Fri, Jul 31, 2015 at 2:13 AM, Tomeu Vizoso <tomeu@...euvizoso.net> wrote:
> On 25 July 2015 at 01:20, Kees Cook <keescook@...omium.org> wrote:
>> Many callers either use NULL or const strings for the third argument of
>> clk_register_clkdev. For those that do not, this is a risk for format
>> strings being accidentally processed (for example in device names). This
>> adds the missing "%s" arguments to make sure format strings will not leak
>> into the clkdev.
>>
>> Signed-off-by: Kees Cook <keescook@...omium.org>
>> ---
>
> [...]
>
>> diff --git a/drivers/clk/tegra/clk.c b/drivers/clk/tegra/clk.c
>> index 41cd87c67be6..97d9fb7e89ad 100644
>> --- a/drivers/clk/tegra/clk.c
>> +++ b/drivers/clk/tegra/clk.c
>> @@ -296,7 +296,7 @@ void __init tegra_register_devclks(struct tegra_devclk *dev_clks, int num)
>>
>>         for (i = 0; i < num; i++, dev_clks++)
>>                 clk_register_clkdev(clks[dev_clks->dt_id], dev_clks->con_id,
>> -                               dev_clks->dev_id);
>> +                               "%s", dev_clks->dev_id);
>
> This causes clocks to be registered with a dev_id string of "(null)",
> which is causing lookups that used to succeed before to fail.

Oh yuck. Yeah, clk_register_clkdev handles a NULL argument differently
than other format-string style functions. Using
clk_register_clkdev(..., dev_clks->dev_id ? "%s" : NULL,
dev_clks->dev_id) seems really ugly to work around this, though.
Perhaps the format string capability should be removed?

-Kees

-- 
Kees Cook
Chrome OS Security
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