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Message-ID: <d8262b12-3ac9-8608-fc6f-d48c33a4225e@linux.alibaba.com>
Date:   Wed, 29 Nov 2023 23:02:01 +0800
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Subject: Re: [PATCH net] net/netfilter: bpf: avoid leakage of skb
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To:     Florian Westphal <fw@strlen.de>
Cc:     pablo@netfilter.org, kadlec@netfilter.org, bpf@vger.kernel.org,
        linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
        coreteam@netfilter.org, netfilter-devel@vger.kernel.org,
        davem@davemloft.net, edumazet@google.com, kuba@kernel.org,
        pabeni@redhat.com, ast@kernel.org
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 <aa83bf32-789f-fec2-ea42-74b0ae05426e@linux.alibaba.com>
 <20231129144736.GB24754@breakpoint.cc>
From:   "D. Wythe" <alibuda@linux.alibaba.com>
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On 11/29/23 10:47 PM, Florian Westphal wrote:
> D. Wythe <alibuda@linux.alibaba.com> wrote:
>> And my origin intention was to allow ebpf progs to return NF_STOLEN, we are
>> trying to modify some netfilter modules via ebpf,
>> and some scenarios require the use of NF_STOLEN, but from your description,
> NF_STOLEN can only be supported via a trusted helper, as least as far as
> I understand.
>
> Otherwise verifier would have to guarantee that any branch that returns
> NF_STOLEN has released the skb, or passed it to a function that will
> release the skb in the near future.

Thank you very much for your help. I now understand the difficulty here.
The verifier cannot determine whether the consume_skb() was executed or not,
when the return value  goes to NF_STOLEN.

We may use NF_DROP at first, it won't be make much difference for us now.

Also, do you have any plans to support this helper?

Best wishes,
D. Wythe