linux-kernel - Re: [PATCH] USB: USBHID: Fix race between disconnect and hiddev

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Message-Id: <201012042122.23852.oliver@neukum.org>
Date:	Sat, 4 Dec 2010 21:22:23 +0100
From:	Oliver Neukum <oliver@...kum.org>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Valentine Barshak <vbarshak@...sta.com>,
	Jiri Kosina <jkosina@...e.cz>, linux-usb@...r.kernel.org,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] USB: USBHID: Fix race between disconnect and hiddev_ioctl

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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