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Date: Tue, 10 Mar 2026 13:33:25 +0100
From: Florian Westphal <fw@strlen.de>
To: Pablo Neira Ayuso <pablo@netfilter.org>
Cc: netdev@vger.kernel.org, Paolo Abeni <pabeni@redhat.com>,
	"David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, netfilter-devel@vger.kernel.org
Subject: Re: [PATCH net 00/10] netfilter: updates for net
Message-ID: <abAPlfmkO7gr142k@strlen.de>
References: <20260309210845.15657-1-fw@strlen.de>
 <aa_4w9gXCkzQ06Nk@chamomile>
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Pablo Neira Ayuso <pablo@netfilter.org> wrote:
> On Mon, Mar 09, 2026 at 10:08:35PM +0100, Florian Westphal wrote:
> > 7-9) fix access bugs in the ctnetlink expectation handling.
> >      Problem is that while RCU prevents the referenced nf_conn entry
> >      from going way, nf_conn entries have an extension area that can
> >      only be safely accessed if the cpu holds a reference to the
> >      conntrack.  Else the extension area can be free'd at any time.
> >      Fix is to grab references before the accesses happen.
> >      These bugs are old, v3.10 resp. even pre-git days.
> >      All fixes from Hyunwoo Kim.
> 
> I am not sure 7-9 are correct.
> 
> nfct_help() is accessed via exp->master in other existing paths,
> I think these fixes are papering an underlying problem since the
> typesafe rcu infrastructure was introduced in nf_conntrack.

AFAICS these patchers are correct and other areas need to be fixed too.
I am currently auditing other conntrack helper usage for this bug
type.  I'm working as fast as I can given the volume of bugs coming
in.  I don't think that not taking these patches now is better in any
way.

Its possible these changes do miss a check for confirmed bit, to
avoid handling new, unconfirmed conntracks during object reuse.

Expect further patches in this area.

But I'm not sure this is related to rcu infra usage.

I would not be surprised if this bug has always been there:
20+ years ago, without KASAN/UBSAN it would likely have never
been found.