Jann Horn reports a use-after-free on disconnect of a USB Ethernet (ax88179_178a.c). Oleksij Rempel has witnessed the same issue with a different driver (ax88172a.c). Jann's report (linked below) explains the root cause in great detail. Briefly, USB Ethernet drivers schedule work (usbnet_deferred_kevent()) which in turn schedules another work (linkwatch_event()). The problem is that usbnet_disconnect() first synchronizes with linkwatch_event() and only then with usbnet_deferred_kevent(). That allows usbnet_deferred_kevent() to schedule another linkwatch_event() after synchronization with the latter. In other words, scheduling happens in AB order and synchronization on disconnect happens in BA order. The correct order is to first synchronize with usbnet_deferred_kevent() (and prevent any future execution), then with linkwatch_event(), i.e. in AB order. Reported-by: Jann Horn <jannh@xxxxxxxxxx> Link: https://lore.kernel.org/netdev/CAG48ez0MHBbENX5gCdHAUXZ7h7s20LnepBF-pa5M=7Bi-jZrEA@xxxxxxxxxxxxxx/ Reported-by: Oleksij Rempel <o.rempel@xxxxxxxxxxxxxx> Link: https://lore.kernel.org/netdev/20220315113841.GA22337@xxxxxxxxxxxxxx/ Signed-off-by: Lukas Wunner <lukas@xxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx Cc: Oliver Neukum <oneukum@xxxxxxxx> Cc: Andrew Lunn <andrew@xxxxxxx> --- drivers/net/usb/usbnet.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c index 9a6450f796dc..6c67ae48afeb 100644 --- a/drivers/net/usb/usbnet.c +++ b/drivers/net/usb/usbnet.c @@ -469,6 +469,9 @@ static enum skb_state defer_bh(struct usbnet *dev, struct sk_buff *skb, */ void usbnet_defer_kevent (struct usbnet *dev, int work) { + if (dev->intf->condition == USB_INTERFACE_UNBINDING) + return; + set_bit (work, &dev->flags); if (!schedule_work (&dev->kevent)) netdev_dbg(dev->net, "kevent %s may have been dropped\n", usbnet_event_names[work]); @@ -1619,11 +1622,11 @@ void usbnet_disconnect (struct usb_interface *intf) if (dev->driver_info->unbind) dev->driver_info->unbind(dev, intf); + cancel_work_sync(&dev->kevent); + net = dev->net; unregister_netdev (net); - cancel_work_sync(&dev->kevent); - usb_scuttle_anchored_urbs(&dev->deferred); usb_kill_urb(dev->interrupt); -- 2.35.2
