netfilter: nf_tables: Fix entries val in rule reset audit log

The value in idx and the number of rules handled in that particular
__nf_tables_dump_rules() call is not identical. The former is a cursor
to pick up from if multiple netlink messages are needed, so its value is
ever increasing. Fixing this is not just a matter of subtracting s_idx
from it, though: When resetting rules in multiple chains,
__nf_tables_dump_rules() is called for each and cb->args[0] is not
adjusted in between. Introduce a dedicated counter to record the number
of rules reset in this call in a less confusing way.

While being at it, prevent the direct return upon buffer exhaustion: Any
rules previously dumped into that skb would evade audit logging
otherwise.

Fixes: 9b5ba5c9c5109 ("netfilter: nf_tables: Unbreak audit log reset")
Signed-off-by: Phil Sutter <[e-mail]>
Reviewed-by: Florian Westphal <[e-mail]>
Signed-off-by: Pablo Neira Ayuso <[e-mail]>

net/netfilter/nf_tables_api.c

···
 	struct net *net = sock_net(skb->sk);
 	const struct nft_rule *rule, *prule;
 	unsigned int s_idx = cb->args[0];
+	unsigned int entries = 0;
+	int ret = 0;
 	u64 handle;
 
 	prule = NULL;
···
 					NFT_MSG_NEWRULE,
 					NLM_F_MULTI | NLM_F_APPEND,
 					table->family,
-					table, chain, rule, handle, reset) < 0)
-			return 1;
-
+					table, chain, rule, handle, reset) < 0) {
+			ret = 1;
+			break;
+		}
+		entries++;
 		nl_dump_check_consistent(cb, nlmsg_hdr(skb));
 cont:
 		prule = rule;
···
 		(*idx)++;
 	}
 
-	if (reset && *idx)
-		audit_log_rule_reset(table, cb->seq, *idx);
+	if (reset && entries)
+		audit_log_rule_reset(table, cb->seq, entries);
 
-	return 0;
+	return ret;
 }
 
 static int nf_tables_dump_rules(struct sk_buff *skb,