netfilter: load nf_log_syslog on enabling nf_conntrack_log_invalid

When no logger is registered, nf_conntrack_log_invalid fails to log invalid
packets, leaving users unaware of actual invalid traffic. Improve this by
loading nf_log_syslog, similar to how 'iptables -I FORWARD 1 -m conntrack
--ctstate INVALID -j LOG' triggers it.

Suggested-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Zi Li <zi.li@linux.dev>
Signed-off-by: Lance Yang <lance.yang@linux.dev>
Acked-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 26 insertions, 0 deletions

diff --git a/net/netfilter/nf_log.c b/net/netfilter/nf_log.c
index 6dd0de33eebd..74cef8bf554c 100644
--- a/net/netfilter/nf_log.c
+++ b/net/netfilter/nf_log.c
@@ -125,6 +125,32 @@ void nf_log_unregister(struct nf_logger *logger)
 }
 EXPORT_SYMBOL(nf_log_unregister);
 
+/**
+ * nf_log_is_registered - Check if any logger is registered for a given
+ * protocol family.
+ *
+ * @pf: Protocol family
+ *
+ * Returns: true if at least one logger is active for @pf, false otherwise.
+ */
+bool nf_log_is_registered(u_int8_t pf)
+{
+	int i;
+
+	if (pf >= NFPROTO_NUMPROTO) {
+		WARN_ON_ONCE(1);
+		return false;
+	}
+
+	for (i = 0; i < NF_LOG_TYPE_MAX; i++) {
+		if (rcu_access_pointer(loggers[pf][i]))
+			return true;
+	}
+
+	return false;
+}
+EXPORT_SYMBOL(nf_log_is_registered);
+
 int nf_log_bind_pf(struct net *net, u_int8_t pf,
 		   const struct nf_logger *logger)
 {