Re: [PATCH] clk_register_clkdev: handle callers needing format string

[Tomeu Vizoso]

On 31 July 2015 at 21:03, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> On Fri, Jul 31, 2015 at 2:13 AM, Tomeu Vizoso <tomeu@xxxxxxxxxxxxxxx> wrote:
>> On 25 July 2015 at 01:20, Kees Cook <keescook@xxxxxxxxxxxx> 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@xxxxxxxxxxxx>
>>> ---
>>
>> [...]
>>
>>> 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?

Yeah, that sounds good to me. At least, I don't see as that good of an
idea to save a few lines of code by making the API so prone to
mistakes.

Could this patch be removed from linux-next in the meantime?

Thanks,

Tomeu

> -Kees
>
> --
> Kees Cook
> Chrome OS Security
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