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Date: Wed, 28 May 2025 14:14:19 +0200
From: Florian Westphal <fw@strlen.de>
To: Yafang Shao <laoar.shao@gmail.com>
Cc: pablo@netfilter.org, kadlec@netfilter.org,
	David Miller <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	Simon Horman <horms@kernel.org>, netfilter-devel@vger.kernel.org,
	coreteam@netfilter.org
Subject: Re: [BUG REPORT] netfilter: DNS/SNAT Issue in Kubernetes Environment
Message-ID: <aDb-G3_W6Ep19Zjp@strlen.de>
References: <CALOAHbBj9_TBOQUEX-4CFK_AHp0v6mRETfCw6uWQ0zYB1sBczQ@mail.gmail.com>
 <aDbyDiOBa3_MwsE4@strlen.de>
 <CALOAHbAeVhLAe3o3UL8UOJrCRbRP8mqYZy37CYNHYFa3zss6Zg@mail.gmail.com>
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Yafang Shao <laoar.shao@gmail.com> wrote:
> > And I don't see how you can encounter a DNS reply before at least one
> > request has been committed to the table -- i.e., the conntrack being
> > confirmed here should not exist -- the packet should have been picked up
> > as a reply packet.
> 
> We've been able to consistently reproduce this behavior. Would you
> have any recommended debugging approaches we could try?

Can you figure out why nf_ct_resolve_clash_harder() doesn't handle the
clash?

AFAIU reply tuple is identical while original isn't.  It would be good
to confirm.  If they were the same, I'd have expected
nf_ct_resolve_clash_harder() to merge the conntracks (nf_ct_can_merge()
branch in __nf_ct_resolve_clash).

Could you also dump/show the origin and reply tuples for the existing
entry and the clashing (new) entry?