From: Marcelo Ricardo Leitner <marcelo.leit...@gmail.com>

After db29a9508a92 ("netfilter: conntrack: disable generic tracking for
known protocols"), if the specific helper is built but not loaded
(a standard for most distributions) systems with a restrictive firewall
but weak configuration regarding netfilter modules to load, will
silently stop working.

This patch then puts a warning message so the sysadmin knows where to
start looking into. It's a pr_warn_once regardless of protocol itself
but it should be enough to give a hint on where to look.

Cc: Florian Westphal <f...@strlen.de>
Cc: Daniel Borkmann <dan...@iogearbox.net>
Signed-off-by: Marcelo Ricardo Leitner <marcelo.leit...@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pa...@netfilter.org>
---
 net/netfilter/nf_conntrack_proto_generic.c |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/net/netfilter/nf_conntrack_proto_generic.c 
b/net/netfilter/nf_conntrack_proto_generic.c
index 60865f1..2281be4 100644
--- a/net/netfilter/nf_conntrack_proto_generic.c
+++ b/net/netfilter/nf_conntrack_proto_generic.c
@@ -90,7 +90,13 @@ static int generic_packet(struct nf_conn *ct,
 static bool generic_new(struct nf_conn *ct, const struct sk_buff *skb,
                        unsigned int dataoff, unsigned int *timeouts)
 {
-       return nf_generic_should_process(nf_ct_protonum(ct));
+       bool ret;
+
+       ret = nf_generic_should_process(nf_ct_protonum(ct));
+       if (!ret)
+               pr_warn_once("conntrack: generic helper won't handle protocol 
%d. Please consider loading the specific helper module.\n",
+                            nf_ct_protonum(ct));
+       return ret;
 }
 
 #if IS_ENABLED(CONFIG_NF_CT_NETLINK_TIMEOUT)
-- 
1.7.10.4

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