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

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Message-ID: <4CFE4C96.4000702@mvista.com>
Date:	Tue, 07 Dec 2010 18:02:46 +0300
From:	Valentine Barshak <vbarshak@...sta.com>
To:	Jiri Kosina <jkosina@...e.cz>
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

Jiri Kosina wrote:
> 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.
>   
Thanks!
> (BTW your patches didn't reach mail mailbox, I had to dig them out from 
> mailinglist -- did you receive bounces by any chance?).
>   
Yes, they did bounce.
Thanks,
Val.
> Thanks,
>
>   

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