Messages in this thread | | | Date | Tue, 6 Aug 2019 10:19:37 -0400 (EDT) | From | Alan Stern <> | Subject | Re: KASAN: use-after-free Read in device_release_driver_internal |
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On Tue, 6 Aug 2019, Oliver Neukum wrote:
> Am Donnerstag, den 01.08.2019, 14:47 -0400 schrieb Alan Stern: > > > > I think this must be caused by an unbalanced refcount. That is, > > something must drop one more reference to the device than it takes. > > That would explain why the invalid access occurs inside a single > > bus_remove_device() call, between the klist_del() and > > device_release_driver(). > > > > The kernel log indicates that the device was probed by rndis_wlan, > > rndis_host, and cdc_acm, all of which got errors because of the > > device's bogus descriptors. Probably one of them is messing up the > > refcount. > > Hi, > > you made me look at cdc-acm. I suspect > > cae2bc768d176bfbdad7035bbcc3cdc973eb7984 ("usb: cdc-acm: Decrement tty port's refcount if probe() fail") > > is buggy decrementing the refcount on the interface in destroy() > even before the refcount is increased. > > Unfortunately I cannot tell from the bug report how many and which > interfaces the emulated test device has. Hence it is unclear to me, > when exactly probe() would fail cdc-acm.
Only one interface (numbered 234!).
> If you agree. I am attaching a putative fix.
Your patch adds a line saying:
> + usb_get_intf(acm->control); /* undone in destroy() */
but I don't see any destroy() function in that source file. Did you mean acm_port_destruct()?
In any case, I don't know if this missing "get" would cause the problem, but it might well.
Alan Stern
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