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

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Date:   Thu, 18 Feb 2021 16:20:01 -0500
From:   Richard Guy Briggs <rgb@...hat.com>
To:     Florian Westphal <fw@...len.de>
Cc:     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

On 2021-02-18 13:52, Florian Westphal wrote:
> Richard Guy Briggs <rgb@...hat.com> wrote:
> > On 2021-02-18 09:22, Florian Westphal wrote:
> > > > 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).

Ok, one little inconvenient question: what about GETOBJ_RESET?  That
looks like a hybrid that modifies kernel table counters and reports
synchronously.  That could be a special case call in
nf_tables_dump_obj() and nf_tables_getobj().  Will that cause a storm
per commit?

> > 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.

Coded, testing...

- RGB

--
Richard Guy Briggs <rgb@...hat.com>
Sr. S/W Engineer, Kernel Security, Base Operating Systems
Remote, Ottawa, Red Hat Canada
IRC: rgb, SunRaycer
Voice: +1.647.777.2635, Internal: (81) 32635