linux-kernel - Re: [RFC] avoid (theoretical) conflicts of input device file names

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Message-ID: <20141008213000.GC15198@dtor-ws>
Date:	Wed, 8 Oct 2014 14:30:00 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Richard Leitner <me@...l1n.net>
Cc:	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
	richard.leitner@...data.com
Subject: Re: [RFC] avoid (theoretical) conflicts of input device file names

Hi Richard,

On Wed, Oct 08, 2014 at 10:49:29PM +0200, Richard Leitner wrote:
> Hi,
> currently I discovered the possibility that device file numbers of the input
> subsystem could go negative when the signed int "border" is passed. To fix
> this behaviour I sent a patch a few minutes ago.
> 
> But as the subject says there is currently the (theoretical) possibility that
> the same input device file name is given out twice. This can happen if the
> "input_no" variable had an overflow (due to the fact this is at least at 2^32
> I call the issue theoretical). If such a case occurs a -EEXISTS is returned at
> the creation of the file.
> 
> IMHO it would be a good idea to check if the chosen input device file name
> is valid at the point it is created (which is currently input_allocate_device).
> So you can just increment and check it again until there's a valid number/name
> found for it.
> 
> I'm pretty new to the input subsystem, so what do you think about it?
> Any comments/ideas? Would there be a better place to do such checking?

I do not think it is worth checking. Yes, theoretically you can wrap
around, but practically instantiating at least 2^32 devices will take
too long. If ever it becomes a concern my very distant future relatives
will move the counter to 64 or 128 bit and call it a day.

Thanks.

-- 
Dmitry
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