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. > > > iptables is rather simple representation (no sets), but nftables is > > > more expressive. > > > > That's not true, at least ebtables' among match is implemented using > > sets. :) > > Then better have a look at this implicit set scenario I describe above > because I cannot see how this can work. Sure, I'll give it a try. Cheers, Phil
