CVE-2025-21781

In the Linux kernel, the following vulnerability has been resolved:

batman-adv: fix panic during interface removal

Reference counting is used to ensure that
batadv_hardif_neigh_node and batadv_hard_iface
are not freed before/during
batadv_v_elp_throughput_metric_update work is
finished.

But there isn't a guarantee that the hard if will
remain associated with a soft interface up until
the work is finished.

This fixes a crash triggered by reboot that looks
like this:

Call trace:
 batadv_v_mesh_free+0xd0/0x4dc [batman_adv]
 batadv_v_elp_throughput_metric_update+0x1c/0xa4
 process_one_work+0x178/0x398
 worker_thread+0x2e8/0x4d0
 kthread+0xd8/0xdc
 ret_from_fork+0x10/0x20

(the batadv_v_mesh_free call is misleading,
and does not actually happen)

I was able to make the issue happen more reliably
by changing hardif_neigh->bat_v.metric_work work
to be delayed work. This allowed me to track down
and confirm the fix.

[sven@narfation.org: prevent entering batadv_v_elp_get_throughput without
 soft_iface]