From mboxrd@z Thu Jan  1 00:00:00 1970
From: Pablo Neira Ayuso <pablo@netfilter.org>
Subject: Re: [PATCH nf 1/5] netfilter: nfnl_cthelper: don't report error if
 NFCTH_PRIV_DATA_LEN is empty
Date: Tue, 21 Mar 2017 11:18:28 +0100
Message-ID: <20170321101828.GA1940@salvia>
References: <1489934162-7415-1-git-send-email-zlpnobody@163.com>
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Cc: netfilter-devel@vger.kernel.org, Liping Zhang <zlpnobody@gmail.com>
To: Liping Zhang <zlpnobody@163.com>
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On Sun, Mar 19, 2017 at 10:35:58PM +0800, Liping Zhang wrote:
> From: Liping Zhang <zlpnobody@gmail.com>
> 
> Currently, when we create cthelper via nfnetlink, -EINVAL will be
> returned if the NFCTH_PRIV_DATA_LEN attribute is empty.
> 
> But enforcing the user to specify the NFCTH_PRIV_DATA_LEN attr seems
> unnecessary, so it's better to set the helper->data_len to zero if
> the NFCTH_PRIV_DATA_LEN attribute is empty.
> 
> Found by running example program from libnetfilter_cthelper:
>   # ./libnetfilter_cthelper/examples/nfct-helper-add test 1
>   error: Invalid argument

I suggest you fix this userspace example instead, we should always
send NFCTH_PRIV_DATA_LEN. This is integral part of the helper
description.

NFCTH_ATTR_PRIV_DATA_LEN has been always set from the conntrack-tools,
so most likely this example just got outdated at some point of the
development and nobody noticed so far.

Thanks.