Commit 46408ea5 authored Feb 08, 2018 by AMAN DEEP Committed by Greg Kroah-Hartman Feb 15, 2018

usb: ohci: Proper handling of ed_rm_list to handle race condition between...


usb: ohci: Proper handling of ed_rm_list to handle race condition between usb_kill_urb() and finish_unlinks()

There is a race condition between finish_unlinks->finish_urb() function
and usb_kill_urb() in ohci controller case. The finish_urb calls
spin_unlock(&ohci->lock) before usb_hcd_giveback_urb() function call,
then if during this time, usb_kill_urb is called for another endpoint,
then new ed will be added to ed_rm_list at beginning for unlink, and
ed_rm_list will point to newly added.

When finish_urb() is completed in finish_unlinks() and ed->td_list
becomes empty as in below code (in finish_unlinks() function):

        if (list_empty(&ed->td_list)) {
                *last = ed->ed_next;
                ed->ed_next = NULL;
        } else if (ohci->rh_state == OHCI_RH_RUNNING) {
                *last = ed->ed_next;
                ed->ed_next = NULL;
                ed_schedule(ohci, ed);
        }

The *last = ed->ed_next will make ed_rm_list to point to ed->ed_next
and previously added ed by usb_kill_urb will be left unreferenced by
ed_rm_list. This causes usb_kill_urb() hang forever waiting for
finish_unlink to remove added ed from ed_rm_list.

The main reason for hang in this race condtion is addition and removal
of ed from ed_rm_list in the beginning during usb_kill_urb and later
last* is modified in finish_unlinks().

As suggested by Alan Stern, the solution for proper handling of
ohci->ed_rm_list is to remove ed from the ed_rm_list before finishing
any URBs. Then at the end, we can add ed back to the list if necessary.

This properly handle the updated ohci->ed_rm_list in usb_kill_urb().

Fixes: 977dcfdc ("USB: OHCI: don't lose track of EDs when a controller dies")
Acked-by: Alan Stern <stern@rowland.harvard.edu>
CC: <stable@vger.kernel.org>
Signed-off-by: Aman Deep <aman.deep@samsung.com>
Signed-off-by: Jeffy Chen <jeffy.chen@rock-chips.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 91b11935

drivers/usb/host/ohci-q.c

+10 −7

Original line number	Original line	Diff line number	Diff line
	@@ -1019,6 +1019,8 @@ static void finish_unlinks(struct ohci_hcd *ohci)
	* have modified this list. normally it's just prepending		* have modified this list. normally it's just prepending
	* entries (which we'd ignore), but paranoia won't hurt.		* entries (which we'd ignore), but paranoia won't hurt.
	*/		*/
			*last = ed->ed_next;
			ed->ed_next = NULL;
	modified = 0;		modified = 0;

	/* unlink urbs as requested, but rescan the list after		/* unlink urbs as requested, but rescan the list after
	@@ -1077,20 +1079,21 @@ static void finish_unlinks(struct ohci_hcd *ohci)
	goto rescan_this;		goto rescan_this;

	/*		/*
	* If no TDs are queued, take ED off the ed_rm_list.		* If no TDs are queued, ED is now idle.
	* Otherwise, if the HC is running, reschedule.		* Otherwise, if the HC is running, reschedule.
	* If not, leave it on the list for further dequeues.		* If the HC isn't running, add ED back to the
			* start of the list for later processing.
	*/		*/
	if (list_empty(&ed->td_list)) {		if (list_empty(&ed->td_list)) {
	*last = ed->ed_next;
	ed->ed_next = NULL;
	ed->state = ED_IDLE;		ed->state = ED_IDLE;
	list_del(&ed->in_use_list);		list_del(&ed->in_use_list);
	} else if (ohci->rh_state == OHCI_RH_RUNNING) {		} else if (ohci->rh_state == OHCI_RH_RUNNING) {
	*last = ed->ed_next;
	ed->ed_next = NULL;
	ed_schedule(ohci, ed);		ed_schedule(ohci, ed);
	} else {		} else {
			ed->ed_next = ohci->ed_rm_list;
			ohci->ed_rm_list = ed;
			/* Don't loop on the same ED */
			if (last == &ohci->ed_rm_list)
	last = &ed->ed_next;		last = &ed->ed_next;
	}		}