• AMAN DEEP's avatar
    usb: ohci: Proper handling of ed_rm_list to handle race condition between... · 04dcdd0e
    AMAN DEEP authored
    usb: ohci: Proper handling of ed_rm_list to handle race condition between usb_kill_urb() and finish_unlinks()
    
    commit 46408ea5 upstream.
    
    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: default avatarAlan Stern <stern@rowland.harvard.edu>
    CC: <stable@vger.kernel.org>
    Signed-off-by: default avatarAman Deep <aman.deep@samsung.com>
    Signed-off-by: default avatarJeffy Chen <jeffy.chen@rock-chips.com>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    
    04dcdd0e
ohci-q.c 33.5 KB