From mboxrd@z Thu Jan 1 00:00:00 1970 From: Valentine Barshak Subject: Re: [PATCH] USB: USBHID: Fix race between disconnect and hiddev_ioctl Date: Sat, 04 Dec 2010 02:31:59 +0300 Message-ID: <4CF97DEF.7020403@mvista.com> References: <20101203172746.GA31045@mvista.com> <20101203231611.GB22969@core.coreip.homeip.net> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20101203231611.GB22969-WlK9ik9hQGAhIp7JRqBPierSzoNAToWh@public.gmane.org> Sender: linux-usb-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Dmitry Torokhov Cc: Jiri Kosina , linux-usb-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-input-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-input@vger.kernel.org Dmitry Torokhov wrote: > On Fri, Dec 03, 2010 at 08:27:46PM +0300, 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. >> > > 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 ;) > > Well, some of the commands were already using the lock, while a couple of them doesn't seem to need it. I've just added locking to the other commands that needed it. I guess I didn't want to rework the whole stuff in order not to forget to unlock and return. But I agree, the code would look a bit cleaner though if did as you say. Thanks, Val. -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html