netfilter: nf_tables: do not allow RULE_ID to refer to another chain

When doing lookups for rules on the same batch by using its ID, a rule from
a different chain can be used. If a rule is added to a chain but tries to
be positioned next to a rule from a different chain, it will be linked to
chain2, but the use counter on chain1 would be the one to be incremented.

When looking for rules by ID, use the chain that was used for the lookup by
name. The chain used in the context copied to the transaction needs to
match that same chain. That way, struct nft_rule does not need to get
enlarged with another member.

Fixes: 1a94e38d254b ("netfilter: nf_tables: add NFTA_RULE_ID attribute")
Fixes: 75dd48e2e420 ("netfilter: nf_tables: Support RULE_ID reference in new rule")
Signed-off-by: Thadeu Lima de Souza Cascardo <[e-mail]>
Cc: <[e-mail]>
Signed-off-by: Pablo Neira Ayuso <[e-mail]>

net/netfilter/nf_tables_api.c

···
 }
 
 static struct nft_rule *nft_rule_lookup_byid(const struct net *net,
+					     const struct nft_chain *chain,
 					     const struct nlattr *nla);
 
 #define NFT_RULE_MAXEXPRS	128
···
 				return PTR_ERR(old_rule);
 			}
 		} else if (nla[NFTA_RULE_POSITION_ID]) {
-			old_rule = nft_rule_lookup_byid(net, nla[NFTA_RULE_POSITION_ID]);
+			old_rule = nft_rule_lookup_byid(net, chain, nla[NFTA_RULE_POSITION_ID]);
 			if (IS_ERR(old_rule)) {
 				NL_SET_BAD_ATTR(extack, nla[NFTA_RULE_POSITION_ID]);
 				return PTR_ERR(old_rule);
···
 }
 
 static struct nft_rule *nft_rule_lookup_byid(const struct net *net,
+					     const struct nft_chain *chain,
 					     const struct nlattr *nla)
 {
 	struct nftables_pernet *nft_net = nft_pernet(net);
···
 		struct nft_rule *rule = nft_trans_rule(trans);
 
 		if (trans->msg_type == NFT_MSG_NEWRULE &&
+		    trans->ctx.chain == chain &&
 		    id == nft_trans_rule_id(trans))
 			return rule;
 	}
···
 
 			err = nft_delrule(&ctx, rule);
 		} else if (nla[NFTA_RULE_ID]) {
-			rule = nft_rule_lookup_byid(net, nla[NFTA_RULE_ID]);
+			rule = nft_rule_lookup_byid(net, chain, nla[NFTA_RULE_ID]);
 			if (IS_ERR(rule)) {
 				NL_SET_BAD_ATTR(extack, nla[NFTA_RULE_ID]);
 				return PTR_ERR(rule);