ice: Fix use after free during unload with ports in bridge

Unloading the ice driver while switchdev port representors are added to
a bridge can lead to kernel panic. Reproducer:

  modprobe ice

  devlink dev eswitch set $PF1_PCI mode switchdev

  ip link add $BR type bridge
  ip link set $BR up

  echo 2 > /sys/class/net/$PF1/device/sriov_numvfs
  sleep 2

  ip link set $PF1 master $BR
  ip link set $VF1_PR master $BR
  ip link set $VF2_PR master $BR
  ip link set $PF1 up
  ip link set $VF1_PR up
  ip link set $VF2_PR up
  ip link set $VF1 up

  rmmod irdma ice

When unloading the driver, ice_eswitch_detach() is eventually called as
part of VF freeing. First, it removes a port representor from xarray,
then unregister_netdev() is called (via repr->ops.rem()), finally
representor is deallocated. The problem comes from the bridge doing its
own deinit at the same time. unregister_netdev() triggers a notifier
chain, resulting in ice_eswitch_br_port_deinit() being called. It should
set repr->br_port = NULL, but this does not happen since repr has
already been removed from xarray and is not found. Regardless, it
finishes up deallocating br_port. At this point, repr is still not freed
and an fdb event can happen, in which ice_eswitch_br_fdb_event_work()
takes repr->br_port and tries to use it, which causes a panic (use after
free).

Note that this only happens with 2 or more port representors added to
the bridge, since with only one representor port, the bridge deinit is
slightly different (ice_eswitch_br_port_deinit() is called via
ice_eswitch_br_ports_flush(), not ice_eswitch_br_port_unlink()).

Trace:
  Oops: general protection fault, probably for non-canonical address 0xf129010fd1a93284: 0000 [#1] PREEMPT SMP KASAN NOPTI
  KASAN: maybe wild-memory-access in range [0x8948287e8d499420-0x8948287e8d499427]
  (...)
  Workqueue: ice_bridge_wq ice_eswitch_br_fdb_event_work [ice]
  RIP: 0010:__rht_bucket_nested+0xb4/0x180
  (...)
  Call Trace:
   (...)
   ice_eswitch_br_fdb_find+0x3fa/0x550 [ice]
   ? __pfx_ice_eswitch_br_fdb_find+0x10/0x10 [ice]
   ice_eswitch_br_fdb_event_work+0x2de/0x1e60 [ice]
   ? __schedule+0xf60/0x5210
   ? mutex_lock+0x91/0xe0
   ? __pfx_ice_eswitch_br_fdb_event_work+0x10/0x10 [ice]
   ? ice_eswitch_br_update_work+0x1f4/0x310 [ice]
   (...)

A workaround is available: brctl setageing $BR 0, which stops the bridge
from adding fdb entries altogether.

Change the order of operations in ice_eswitch_detach(): move the call to
unregister_netdev() before removing repr from xarray. This way
repr->br_port will be correctly set to NULL in
ice_eswitch_br_port_deinit(), preventing a panic.

Fixes: fff292b ("ice: add VF representors one by one")
Reviewed-by: Michal Swiatkowski <michal.swiatkowski@linux.intel.com>
Reviewed-by: Paul Menzel <pmenzel@molgen.mpg.de>
Signed-off-by: Marcin Szycik <marcin.szycik@linux.intel.com>
Tested-by: Sujai Buvaneswaran <sujai.buvaneswaran@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

drivers/net/ethernet/intel/ice/ice_eswitch.c

@@ -552,13 +552,14 @@ int ice_eswitch_attach_sf(struct ice_pf *pf, struct ice_dynamic_port *sf)
 static void ice_eswitch_detach(struct ice_pf *pf, struct ice_repr *repr)
 {
 	ice_eswitch_stop_reprs(pf);
+	repr->ops.rem(repr);
+
 	xa_erase(&pf->eswitch.reprs, repr->id);
 
 	if (xa_empty(&pf->eswitch.reprs))
 		ice_eswitch_disable_switchdev(pf);
 
 	ice_eswitch_release_repr(pf, repr);
-	repr->ops.rem(repr);
 	ice_repr_destroy(repr);
 
 	if (xa_empty(&pf->eswitch.reprs)) {