[PATCH net v1] mac802154: drain mac_wq before unregistering interfaces

From: Xuanqiang Luo <redacted>

ieee802154_unregister_hw() unregisters the wpan netdevs before
destroying mac_wq. The RX path stores the receiving sub-interface
(sdata) in the queued MAC command descriptor without taking a
reference to the netdev.

If mac802154_rx_mac_cmd_worker() runs after the netdev has been freed,
it dereferences the stale pointer and triggers a KASAN
slab-use-after-free:

  BUG: KASAN: slab-use-after-free in mac802154_rx_mac_cmd_worker+0xc0/0x498 [mac802154]
  Read of size 8 at addr ffff0000c6db0ba8 by task kworker/u16:3/61
  ...
  Call trace:
   show_stack+0x20/0x38 (C)
   dump_stack_lvl+0x78/0x90
   print_address_description.constprop.0+0x88/0x398
   print_report+0xa8/0x278
   kasan_report+0xa8/0xf8
   __asan_load8+0x9c/0xc0
   mac802154_rx_mac_cmd_worker+0xc0/0x498 [mac802154]
   process_one_work+0x334/0x8b8
  ...
  Allocated by task 630:
   kasan_save_stack+0x2c/0x58
   kasan_save_track+0x20/0x40
   kasan_save_alloc_info+0x40/0x58
   __kasan_kmalloc+0xa0/0xb8
   __kvmalloc_node_noprof+0x1e8/0x588
   alloc_netdev_mqs+0x74/0x7f0
   ieee802154_if_add+0xac/0x630 [mac802154]
   ieee802154_register_hw+0x31c/0x3d0 [mac802154]
   fakelb_add_one+0x250/0x318 [fakelb]
  ...
  Freed by task 652:
   kasan_save_stack+0x2c/0x58
   kasan_save_track+0x20/0x40
   kasan_save_free_info+0x4c/0x78
   __kasan_slab_free+0x60/0x90
   kfree+0x194/0x478
   kvfree+0x44/0x60
   netdev_release+0x4c/0x68
   device_release+0xac/0x130
   kobject_cleanup+0x84/0x248
   kobject_put+0x98/0xf8
   netdev_run_todo+0x3a0/0x5e0
   rtnl_unlock+0x18/0x30
   ieee802154_unregister_hw+0x48/0x90 [mac802154]
   fakelb_remove+0xe8/0x148 [fakelb]

After killing local->tasklet, drain mac_wq before calling
ieee802154_remove_interfaces() so pending work completes before the
interfaces are unregistered. Do this without holding rtnl because scan
and beacon workers acquire it themselves.

Fixes: d021d218f6d9 ("mac802154: Handle received BEACON_REQ")
Signed-off-by: Xuanqiang Luo <redacted>
---
 net/mac802154/main.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/net/mac802154/main.c b/net/mac802154/main.c
index ea1efef3572ae..dc80184d7d091 100644
--- a/net/mac802154/main.c
+++ b/net/mac802154/main.c

@@ -276,6 +276,11 @@ void ieee802154_unregister_hw(struct ieee802154_hw *hw)
 
 	tasklet_kill(&local->tasklet);
 	flush_workqueue(local->workqueue);
+	/*
+	 * Drain mac_wq before unregistering interfaces; some workers access
+	 * sub-interface data and acquire rtnl themselves.
+	 */
+	drain_workqueue(local->mac_wq);
 
 	rtnl_lock();
 

-- 
2.43.0