Re: [nf-next PATCH v2] netfilter: nf_tables: Introduce NFTA_RULE_ACTUAL_EXPR

[Pablo Neira Ayuso <pablo@netfilter.org>]

On Mon, Feb 06, 2023 at 10:52:29AM +0100, Pablo Neira Ayuso wrote:
> On Sat, Feb 04, 2023 at 10:00:25PM +0100, Phil Sutter wrote:
> > On Sat, Feb 04, 2023 at 10:41:37AM +0100, Pablo Neira Ayuso wrote:
> > > On Fri, Feb 03, 2023 at 05:21:29PM +0100, Phil Sutter wrote:
> > > [...]
> > > > On Fri, Feb 03, 2023 at 04:32:01PM +0100, Pablo Neira Ayuso wrote:
> > > [...]
> > > > > I also wonder if this might cause problems with nftables and implicit
> > > > > sets, they are bound to one single lookup expression that, when gone,
> > > > > the set is released. Now you will have two expressions pointing to an
> > > > > implicit set. Same thing with implicit chains. This might get tricky
> > > > > with the transaction interface.
> > > > 
> > > > While indeed two lookup expressions will refer to the same anonymous
> > > > set, only one of those expressions will ever be in use. There's no way
> > > > the kernel would switch between rule variants (or use both at the same
> > > > time).
> > > 
> > > OK, but control plane will reject two lookup expressions that refer to
> > > the same anonymous set.
> > 
> > Only if it sees the second expression: If NFTA_RULE_ACTUAL_EXPR is
> > present, the kernel will copy the content of NFTA_RULE_EXPRESSIONS into
> > a buffer pointed to by nft_rule::dump_expr. It does not inspect the
> > content apart from nla_policy checking which merely ensures it's a
> > nested array of elements conforming to nft_expr_policy (i.e., have a
> > NAME and DATA attribute).
> > 
> > The copied data is touched only by nf_tables_fill_rule_info() which
> > copies it as-is into the skb. Later, nf_tables_rule_destroy() just frees
> > the whole blob.
> > 
> > So effectively the kernel doesn't know or care what expressions are
> > contained in NFTA_RULE_EXPRESSIONS.
> 
> Copy should work, sorry I thought you were parsing the expression again.

If you are happy with this, then let's place it in nf-next?