linux-kernel - Re: [PATCH net] netfilter: br_netfilter: reread nf

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Message-ID: <aKbDZWHNf4_Nktsm@strlen.de>
Date: Thu, 21 Aug 2025 08:57:41 +0200
From: Florian Westphal <fw@...len.de>
To: Wang Liang <wangliang74@...wei.com>
Cc: pablo@...filter.org, kadlec@...filter.org, razor@...ckwall.org,
	idosch@...dia.com, davem@...emloft.net, edumazet@...gle.com,
	kuba@...nel.org, pabeni@...hat.com, horms@...nel.org,
	yuehaibing@...wei.com, zhangchangzhong@...wei.com,
	netfilter-devel@...r.kernel.org, coreteam@...filter.org,
	bridge@...ts.linux.dev, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] netfilter: br_netfilter: reread nf_conn from skb
 after confirm()

Wang Liang <wangliang74@...wei.com> wrote:
> 
> 在 2025/8/20 19:31, Florian Westphal 写道:
> > Wang Liang <wangliang74@...wei.com> wrote:
> > > Previous commit 2d72afb34065 ("netfilter: nf_conntrack: fix crash due to
> > > removal of uninitialised entry") move the IPS_CONFIRMED assignment after
> > > the hash table insertion.
> > How is that related to this change?
> > As you write below, the bug came in with 62e7151ae3eb.
> 
> Before the commit 2d72afb34065, __nf_conntrack_confirm() set
> 'ct->status |= IPS_CONFIRMED;' before check hash, the warning will not
> happen, so I put it here.

Oh, right, the problem was concealed before this.

> > There is a second bug here, confirm can return NF_DROP and
> > nfct will be NULL.
> 
> Thanks for your suggestion!
> 
> Do you mean that ct may be deleted in confirm and return NF_DROP, so we can
> not visit it in br_nf_local_in() and need to add 'case NF_DROP:' here?
>
> I cannot find somewhere set skb->_nfct to NULL and return NF_DROP. Can you
> give some hints?

You are right, skb->_nfct isn't set to NULL in case NF_DROP is returned.
However, the warning will trigger as we did not insert the conntrack
entry in that case.

I suggest to remove the warning, I don't think it buys anything.

Thanks.