net/netfilter: add nf_conntrack_ipv4 compat module for kube-proxy

kube-proxy won't enable ipvs unless it can modprobe nf_conntrack_ipv4 and
find it in the list of loaded modules afterward.  Thus an alias isn't
enough to maintain compatibility; we need an actual module.

net/netfilter/Kconfig

@@ -70,6 +70,14 @@ config NF_CONNTRACK
 
 	  To compile it as a module, choose M here.  If unsure, say N.
 
+config NF_CONNTRACK_IPV4_COMPAT
+	tristate "Netfilter connection tracking IPv4 compatibility module"
+	depends on NF_CONNTRACK
+	default NF_CONNTRACK
+	help
+	  Compatibility nf_conntrack_ipv4 module that loads nf_conntrack.ko,
+	  since kube-proxy cares about the names of loaded kernel modules.
+
 config NF_LOG_COMMON
 	tristate
 

net/netfilter/Makefile

@@ -24,6 +24,7 @@ obj-$(CONFIG_NETFILTER_NETLINK_OSF) += nfnetlink_osf.o
 
 # connection tracking
 obj-$(CONFIG_NF_CONNTRACK) += nf_conntrack.o
+obj-$(CONFIG_NF_CONNTRACK_IPV4_COMPAT) += nf_conntrack_ipv4.o
 
 obj-$(CONFIG_NF_CT_PROTO_GRE) += nf_conntrack_proto_gre.o
 

net/netfilter/nf_conntrack_ipv4.c

@@ -0,0 +1,31 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Compatibility nf_conntrack_ipv4 module that depends on nf_conntrack
+ * to keep kube-proxy happy.
+ *
+ * Copyright (c) 2018 Red Hat, Inc.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation; either version 2 of the License, or (at your option)
+ * any later version.
+ */
+
+#include <linux/module.h>
+#include <linux/printk.h>
+#include <net/netfilter/nf_conntrack.h>
+
+unsigned int *pointer_to_nf_conntrack_data = &nf_conntrack_max;
+
+static int __init nf_conntrack_ipv4_init(void) {
+	pr_notice("nf_conntrack_ipv4: loaded compatibility alias for nf_conntrack\n");
+	return 0;
+}
+
+static void __exit nf_conntrack_ipv4_exit(void) {}
+
+module_init(nf_conntrack_ipv4_init);
+module_exit(nf_conntrack_ipv4_exit);
+
+MODULE_DESCRIPTION("kube-proxy compatibility wrapper for nf_conntrack.ko");
+MODULE_LICENSE("GPL");