linux-kernel - Re: [PATCH ghak124 v3] audit: log nftables configuration change events

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Message-ID: <20210218125248.GB22944@breakpoint.cc>
Date:   Thu, 18 Feb 2021 13:52:48 +0100
From:   Florian Westphal <fw@...len.de>
To:     Richard Guy Briggs <rgb@...hat.com>
Cc:     Florian Westphal <fw@...len.de>, Phil Sutter <phil@....cc>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-Audit Mailing List <linux-audit@...hat.com>,
        netfilter-devel@...r.kernel.org, twoerner@...hat.com,
        Eric Paris <eparis@...isplace.org>, tgraf@...radead.org
Subject: Re: [PATCH ghak124 v3] audit: log nftables configuration change
 events

Richard Guy Briggs <rgb@...hat.com> wrote:
> On 2021-02-18 09:22, Florian Westphal wrote:
> > No.  There is a hierarchy, e.g. you can't add a chain without first
> > adding a table, BUT in case the table was already created by an earlier
> > transaction it can also be stand-alone.
> 
> Ok, so there could be a stand-alone chain mod with one table, then a
> table add of a different one with a "higher ranking" op...

Yes, that can happen.

> > > It seems I'd need to filter out the NFT_MSG_GET_* ops.
> > 
> > No need, the GET ops do not cause changes and will not trigger a
> > generation id change.
> 
> Ah, so it could trigger on generation change.  Would GET ops be included
> in any other change

No, GET ops are standalone, they cannot be part of a transaction.
If you look at

static const struct nfnl_callback nf_tables_cb[NFT_MSG_MAX] = {

array in nf_tables_api.c, then those ops with a '.call_batch' can
appear in transaction (i.e., can cause modification).

The other ones (.call_rcu) are read-only.

If they appear in a batch tehy will be ignored, if the batch consists of
such non-modifying ops only then nf_tables_commit() returns early
because the transaction list is empty (nothing to do/change).

> such that it would be desirable to filter them out
> to reduce noise in that single log line if it is attempted to list all
> the change ops?  It almost sounds like it would be better to do one
> audit log line for each table for each family, and possibly for each op
> to avoid the need to change userspace.  This would already be a
> significant improvement picking the highest ranking op.

I think i understand what you'd like to do.  Yes, that would reduce
the log output a lot.