linux-kernel - Re: [Security] Should open TTY device files pin minor numbers?

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Message-ID: <alpine.DEB.1.10.0907291434520.28013@asgard.lang.hm>
Date:	Wed, 29 Jul 2009 14:35:57 -0700 (PDT)
From:	david@...g.hm
To:	"H. Peter Anvin" <hpa@...or.com>
cc:	Greg KH <greg@...ah.com>, Alan Stern <stern@...land.harvard.edu>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	alan@...rguk.ukuu.org.uk
Subject: Re: [Security] Should open TTY device files pin minor numbers?

On Wed, 29 Jul 2009, H. Peter Anvin wrote:

> On 07/24/2009 10:14 PM, Greg KH wrote:
>> On Thu, Jul 23, 2009 at 02:38:01PM -0400, Alan Stern wrote:
>>> Recent work in the TTY core and in usb-serial has caused a change
>>> in behavior between 2.6.30 and 2.6.31-rc.  Namely, if a USB serial
>>> device is unplugged while a process holds the device file open, the
>>> minor number won't get reused until the process closes the file.
>>
>> That's how the usb-serial code always worked, this is nothing new at
>> all.
>>
>>> For example, if you run minicom over /dev/ttyUSB0, unplug the USB
>>> device while minicom is running, and then plug it in again before
>>> exiting minicom, it will reappear as /dev/ttyUSB1 instead of
>>> /dev/ttyUSB0 (which will be gone).
>>
>> Exactly.  People are used to this by now, it shouldn't be a supprise :)
>>
>
> It is, however, a *very* nasty surprise when the USB bus glitches.

however since the serial adapters will be re-detected in a random order 
it's less nasty than cross-connecting devices and applications silently.

David Lang
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