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From: "Serguei Bezverkhi (sbezverk)" <sbezverk@cisco.com>
To: "netfilter-devel@vger.kernel.org" <netfilter-devel@vger.kernel.org>
Cc: Pablo Neira Ayuso <pablo@netfilter.org>,
	Michael Stapelberg <michael@stapelberg.ch>
Subject: Rearranging expressions in the rule
Date: Wed, 30 Oct 2019 14:26:34 +0000	[thread overview]
Message-ID: <FCE200C6-A84D-4689-B1E4-3174C52999F6@contoso.com> (raw)

Hello,

I came across an anomaly (at least I think it is anomaly), but wanted to confirm my observation.  

The following sequence of expressions:
[
{"DestRegister":1,"Base":"expr.PayloadBaseNetworkHeader","Len":1,"Offset":9}, 
{"Op":"expr.CmpOpEq","Register":1,"Data":["0x1"]},
{"DestRegister":1,"Base":"expr.PayloadBaseNetworkHeader","Len":4,"Offset":16},
{"SourceRegister":1,"DestRegister":1,"Len":4,"Mask":["0xff","0xff","0x0","0x0"],"Xor":["0x0","0x0","0x0","0x0"]},
{"Op":"expr.CmpOpEq","Register":1,"Data":["0x1","0x1","0x0","0x0"]},
{"Kind":"0x0"}
]

correctly generates nft like rule:

ip protocol icmp ip daddr 1.1.0.0/16 drop

Then I request netlink to get me the same rule back (I am testing functionality to read and absorb already existing nft rules), I get different set of expressions for the same rule. Here is what I get:
[
{"DestRegister":1,"Base":"expr.PayloadBaseNetworkHeader","Len":1,"Offset":9},
{"Op":"expr.CmpOpEq","Register":1,"Data":["0x1"]},
{"DestRegister":1,"Base":"expr.PayloadBaseNetworkHeader","Len":4,"Offset":16},
{"Op":"expr.CmpOpEq","Register":1,"Data":["0x1","0x1","0x0","0x0"]},
{"Kind":"0x0"}
]

It does not look correct because it loses subnet length information.  I would appreciate if somebody could confirm if it is not expected behavior and if anybody observed something similar.

Thank you
Serguei


                 reply	other threads:[~2019-10-30 14:33 UTC|newest]

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