netfilter: nf_conntrack: log packets dropped by helpers

Log packets dropped by helpers using the netfilter logging API. This
is useful in combination with nfnetlink_log to analyze those packets
in userspace for debugging.

Signed-off-by: Patrick McHardy <kaber@trash.net>

1 files changed, 5 insertions, 1 deletions

diff --git a/net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c b/net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c
index 9ac2fdc36ecc..aa95bb82ee6c 100644
--- a/net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c
+++ b/net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c
@@ -26,6 +26,7 @@
 #include <net/netfilter/ipv4/nf_conntrack_ipv4.h>
 #include <net/netfilter/nf_nat_helper.h>
 #include <net/netfilter/ipv4/nf_defrag_ipv4.h>
+#include <net/netfilter/nf_log.h>
 
 int (*nf_nat_seq_adjust_hook)(struct sk_buff *skb,
                               struct nf_conn *ct,
@@ -113,8 +114,11 @@ static unsigned int ipv4_confirm(unsigned int hooknum,
 
         ret = helper->help(skb, skb_network_offset(skb) + ip_hdrlen(skb),
                            ct, ctinfo);
-        if (ret != NF_ACCEPT)
+        if (ret != NF_ACCEPT) {
+                nf_log_packet(NFPROTO_IPV4, hooknum, skb, in, out, NULL,
+                              "nf_ct_%s: dropping packet", helper->name);
                 return ret;
+        }
 
         if (test_bit(IPS_SEQ_ADJUST_BIT, &ct->status)) {
                 typeof(nf_nat_seq_adjust_hook) seq_adjust;