mac802154: hold an interface reference across the scan worker

mac802154: hold an interface reference across the scan worker

mac802154_scan_worker() captures the scanning sub-interface under RCU
and then keeps dereferencing sdata->dev after rcu_read_unlock() and
outside the rtnl -- in the failure traces, in
mac802154_transmit_beacon_req() (skb->dev = sdata->dev), and in the
end_scan cleanup. Nothing keeps that netdev alive across the worker
iteration.

A concurrent DEL_INTERFACE or PHY removal can unregister the interface
once the worker drops the rtnl between its two drv_set_channel()
sections. unregister_netdevice() frees the netdev asynchronously from
netdev_run_todo() with the rtnl already dropped, so neither holding the
rtnl nor the per-PHY IEEE802154_IS_SCANNING flag prevents a stale worker
iteration from dereferencing the freed netdev -- a KASAN
slab-use-after-free, reachable by racing TRIGGER_SCAN against
DEL_INTERFACE (both CAP_NET_ADMIN).

Pin the netdev with netdev_hold() while the RCU read lock is still held,
and release it at every worker exit.

Fixes: 57588c71177f ("mac802154: Handle passive scanning")
Cc: stable@vger.kernel.org
Signed-off-by: Ibrahim Hashimov <security@auditcode.ai>
Link: https://patch.msgid.link/20260721211228.34578-1-security@auditcode.ai
Signed-off-by: Jakub Kicinski <kuba@kernel.org>