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Date: Thu, 30 Apr 2026 15:27:07 +0200
From: Florian Westphal <fw@strlen.de>
To: Tristan Madani <tristmd@gmail.com>
Cc: Pablo Neira Ayuso <pablo@netfilter.org>, Phil Sutter <phil@nwl.cc>,
	netfilter-devel@vger.kernel.org, netdev@vger.kernel.org,
	stable@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 1/2] netfilter: ip_tables: guard
 ipt_unregister_table_pre_exit against NULL ops
Message-ID: <afNYqx41pBCyDnjR@strlen.de>
References: <20260429175613.1459342-1-tristmd@gmail.com>
 <177750472539.3004201.15967003942391945312@talencesecurity.com>
 <177750474339.3016150.13196470704394042910@talencesecurity.com>
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Tristan Madani <tristmd@gmail.com> wrote:
> ipt_register_table() adds the table to the per-netns list via
> xt_register_table() before assigning the per-net ops copy to
> new_table->ops.  If cleanup_net runs during this window,
> ipt_unregister_table_pre_exit() finds the table via xt_find_table()
> and passes the NULL ops pointer to nf_unregister_net_hooks(), causing
> a general protection fault.
> 
> Guard against this by checking table->ops before calling
> nf_unregister_net_hooks().  If ops is NULL the table is still being
> set up; the register path will either complete and register the hooks
> normally, or fail and clean up via __ipt_unregister_table().

Is there a reproducer for this bug?

This explanation makes little sense to me.
If netns is being destroyed, then there should be no more requests
to set/getsockopt.

Is this perhaps about aggressive rmmod + parallel set/getsockopt calls?
That would make more sense, but this needs a different fix.

I'm working on a new unreg scheme to avoid rmmod racing with concurrent
calls into iptables set/getsockopts.