From: Oliver Neukum <oliver@neukum.org>
To: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Subject: Re: [PATCH] USB: USBHID: Fix race between disconnect and hiddev_ioctl
Date: Sat, 4 Dec 2010 21:22:23 +0100
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Cc: Valentine Barshak <vbarshak@mvista.com>, Jiri Kosina <jkosina@suse.cz>,
        linux-usb@vger.kernel.org, linux-input@vger.kernel.org,
        linux-kernel@vger.kernel.org
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Am Samstag, 4. Dezember 2010, 00:16:12 schrieb Dmitry Torokhov:
> > Since disconnect can happen at any time, we can't initialize
> > struct hid_device *hid = hiddev->hid at the beginning of ioctl
> > and then use it.
> > 
> > This change checks hiddev->exist flag while holding
> > the existancelock and uses hid_device only if it exists.
> 
> Why didn't you take the lock and check hiddev->exist at the beginning of
> ioctl handler instead of pushing it down into individual command
> handlers? I guess it would slow down HIDIOCGVERSION but I think we could
> pay this price for code that is more clear ;)

Strictly speaking you'd change the semantics. Right now you can execute
the ioctl even if you know you are holding an fd to a disconnected device
open.

	Regards
		Oliver
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