netdev - Re: [PATCH] netfilter/nflog: nflog-range does not truncate packets

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Date:	Tue, 7 Jun 2016 19:06:15 -0400
From:	Vishwanath Pai <vpai@...mai.com>
To:	Pablo Neira Ayuso <pablo@...filter.org>
Cc:	kaber@...sh.net, kadlec@...ckhole.kfki.hu,
	netfilter-devel@...r.kernel.org, coreteam@...filter.org,
	johunt@...mai.com, netdev@...r.kernel.org, pai.vishwain@...il.com
Subject: Re: [PATCH] netfilter/nflog: nflog-range does not truncate packets

On 06/06/2016 06:31 PM, Pablo Neira Ayuso wrote:
> On Wed, Jun 01, 2016 at 08:23:54PM -0400, Vishwanath Pai wrote:
>> netfilter/nflog: nflog-range does not truncate packets
>>
>> The --nflog-range parameter from userspace is ignored in the kernel and
>> the entire packet is sent to the userspace. The per-instance parameter
>> copy_range still works, with this change --nflog-range will have
>> preference over copy_range.
> 
> I think it's reasonable to assume that --nflog-range from the rule
> applies globally to any instance.
> 
> However, per-instance copy_range has prevailed over --nflog-range
> since the beginning, so I would follow a more conservative approach,
> ie. remain copy_range in preference over --nflog-range.
> 
> So I'd suggest you invert this logic.
> 
> Let me know, thanks.
> 

Thanks for reviewing this. I think my comment on the patch was
misleading, we do give preference to copy_range and that is what we
default to. --nflog-range will not override the per-instance default,
the only time it would get preference is when its value is lesser than
the per-instance value. If copy_range is lesser than --nflog-range then
we retain copy_range.

So basically what we are doing is min(copy_range, nflog-range). Just
wanted to clarify this, if this is not how it's meant to be please let
me know.

Also, there is a bug in my patch, li->u.ulog.copy_len can be set to "0"
from userspace (if --nflog-range is not specified), so we have to check
for this condition before using the value. I will send a V2 of the patch
based on your reply.

Thanks,
Vishwanath