linux-kernel - Re: Race condition between driver_probe_device and device

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Fri, 7 Dec 2012 21:04:19 +0800
From:	Ming Lei <ming.lei@...onical.com>
To:	Wedson Almeida Filho <wedsonaf@...il.com>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Greg KH <gregkh@...uxfoundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Linux PM List <linux-pm@...r.kernel.org>
Subject: Re: Race condition between driver_probe_device and device_shutdown

On Fri, Dec 7, 2012 at 8:16 PM, Wedson Almeida Filho <wedsonaf@...il.com> wrote:
>> Because device_del() will put reference count of the parent, and the patch
>> only focuses on race between probe/release and shutdown.
>
> Right. device_del() puts the reference count of the parent -- is it
> guaranteed that device_del() won't ever reassign dev->parent though
> (e.g., to NULL)? I don't think it is, so I think that patch should
> also save the pointer to the parent and use it (instead of what
> happens to be in than dev->parent) to release the lock and put the
> ref.
>
>> As far as device_move() concerned, looks it might be a problem.
>> The problem even exits on driver attach vs. device open/release,
>> if device_move is called in open() and open() happens before driver
>> attach completes.
>
> Yeah, the pattern of locking the parent followed by the device occurs
> in a few places. It looks like they were added by Alan with commit
> bf74ad5bc41727d5f2f1c6bedb2c1fac394de731. (And as Greg mentioned,
> might be occurring often enough to merit being moved into a common
> function.)

In fact, there is no shutdown callback defined for usb driver, so holding
the parent lock in device_shutdown() might be removed.

>
> I guess the question is whether the callee is allowed to call
> device_move(), if not, we're good.

Not only the callee, and other contexts can change device->parent
too. Looks rfcomm_tty_open() which calls device_move() is called
in open() context, so the parent might be changed before unlock(dev->parent)
in __driver_attach().

>
>> Your concern on device_remove() might be correct. Also, I am wondering
>> if we can walk the 'dpm_list' backwards for device shutdown, which should
>> be simpler and more reasonable.
>
> How would that help?

device_pm_lock() can prevent device_move() from being running.

Thanks,
--
Ming Lei
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/