Re: [PATCH v2 1/2] netfilter: ip_tables: guard ipt_unregister_table_pre_exit against NULL ops

Tristan Madani
2026-05-01T20:41:08Z

On Thu, 1 May 2026 Florian Westphal wrote:
> If we have races between a thread calling ipt_register_table
> and the netns cleanup path there is nothing we could ever do to
> fix it: we are tearing down a live network namespace.
> Something else must be going on.

I agree, this one is unusual. I tried multiple PoC approaches
without success -- all I have is the syzkaller crash I shared,
no reliable reproducer. Syzkaller itself could not minimize it
either.

That said, the crash is real -- KASAN shows ops=NULL in
pre_exit during cleanup_net -- so something is reaching that
path. The V2 guard handles it regardless of the root cause:
if ops is NULL in pre_exit, we should not pass it to
nf_unregister_net_hooks.

I will share any PoC/repro if I get one.

Thanks,
Tristan