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.
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