linux-kernel - Re: [PATCH 1/2] USB: HID: Fix race between disconnect and hiddev

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Date:	Tue, 7 Dec 2010 15:47:13 +0100 (CET)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Valentine Barshak <vbarshak@...sta.com>
Cc:	linux-usb@...r.kernel.org, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] USB: HID: Fix race between disconnect and
 hiddev_ioctl

On Mon, 6 Dec 2010, Valentine Barshak wrote:

> A USB HID device can be disconnected at any time.
> If this happens right before or while hiddev_ioctl is in progress,
> the hiddev_ioctl tries to access invalid hiddev->hid pointer.
> When the hid device is disconnected, the hiddev_disconnect()
> ends up with a call to hid_device_release() which frees
> hid_device, but doesn't set the hiddev->hid pointer to NULL.
> If the deallocated memory region has been re-used by the kernel,
> this can cause a crash or memory corruption.
> 
> 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.

The code duplication isn't really particularly nice, but I don't see any 
way around it that wouldn't complicate things even more.

I will be applying the patches, thanks.

(BTW your patches didn't reach mail mailbox, I had to dig them out from 
mailinglist -- did you receive bounces by any chance?).

Thanks,

-- 
Jiri Kosina
SUSE Labs, Novell Inc.
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