Re: delete matching rule like it can be done in case of iptables

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Amish

Le 07/12/2021 à 06:29, Amish a écrit :

On 06/12/21 19:17, Daniel wrote:
Hi Amish

Le 06/12/2021 à 14:30, Amish a écrit :
On 06/12/21 18:41, Pablo Neira Ayuso wrote:
On Sun, Dec 05, 2021 at 05:25:29PM +0530, Amish wrote:
Hello,

nftables wiki [1] mentions this:

Note: There are plans to support rule deletion by passing:
% nft delete rule filter output ip saddr 192.168.1.1 counter
Any idea when will this happen? Because I thought it was very important
feature. (unless I missed an alternate way to do it)

I want to migrate from iptables to nftables (from many years) but deleting a
rule via script is not as easy as in case of iptables.

Obtaining the handle first and then deleting it is difficult
programmatically.
You can use --echo and --handle options to fetch the rule handle.

  # nft -e -a  add rule x y counter
  add rule ip x y counter packets 0 bytes 0 # handle 3
  # new generation 5 by process 91190 (nft)

Well then I need to keep recording each rule addition somewhere so that I can delete by handle in future.

Some rules are added manually, some added by scripts. Scripts may want to remove manually added rule.

So its not as easy like in iptables.

In a script you can use eg

myhandle=$(echo `$nft -sa list chain ip mangle prerouting |grep -F "ct state new counter jump MAIN"|grep -oP '(# handle ).*'`|cut -d " " -f 3)
$fwtables delete rule ip mangle prerouting handle $myhandle

and you're done. ip, mangle prerouting and rule to delete could be sended as parameters in a bash function for instance.

[...]

Hi Daniel

Thank you for your reply.

This actually is my basic problem. Rules are complex. They are not as simple as above example.

Hence the parsing (grepping) is not straight forward like in above example.

state may not always be "new". (can be established or related or both)

There may not always be counter in rule.

Some rules may have anonymous sets.

Some rules may have TCP port redirection.

So on ...

I can not write a script for each and every combination to detect the handle.

In case of iptables I can delete the rule by giving exact same expression except instead of giving -A, I just have to give -D.

You don't understand the purpose of the abvoe exemple. More clear:

#!/bin/bash

MyFct {

myhandle=$(echo `$nft -sa list chain $1 $2 $3 |grep -F $4|grep -oP '(# handle ).*'`|cut -d " " -f 3)
$fwtables delete rule $1 $2 $3 handle $myhandle

}

MyFct ip mangle prerouting "ct state new counter jump MAIN"

or

MyFct ip6 filter input "iif \"lan\" ct state invalid drop"

or whatever rule you want to delete

--
Daniel



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