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.
