netfilter: nf_tables: missing error reporting for not selected expres…

…sions

Sometimes users forget to turn on nftables extensions from Kconfig that
they need. In such case, the error reporting from userspace is
misleading:

 $ sudo nft add rule x y counter
 Error: Could not process rule: No such file or directory
 add rule x y counter
 ^^^^^^^^^^^^^^^^^^^^

Add missing NL_SET_BAD_ATTR() to provide a hint:

 $ nft add rule x y counter
 Error: Could not process rule: No such file or directory
 add rule x y counter
              ^^^^^^^

Fixes: 83d9dcb ("netfilter: nf_tables: extended netlink error reporting for expressions")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_tables_api.c

@@ -3328,8 +3328,10 @@ static int nf_tables_newrule(struct sk_buff *skb, const struct nfnl_info *info,
 			if (n == NFT_RULE_MAXEXPRS)
 				goto err1;
 			err = nf_tables_expr_parse(&ctx, tmp, &expr_info[n]);
-			if (err < 0)
+			if (err < 0) {
+				NL_SET_BAD_ATTR(extack, tmp);
 				goto err1;
+			}
 			size += expr_info[n].ops->size;
 			n++;
 		}