net: Add module reference to FIB notifiers

When a listener registers to the FIB notification chain it receives a
dump of the FIB entries and rules from existing address families by
invoking their dump operations.

While we call into these modules we need to make sure they aren't
removed. Do that by increasing their reference count before invoking
their dump operations and decrease it afterwards.

Fixes: 04b1d4e50e ("net: core: Make the FIB notification chain generic")
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/fib_notifier.c

@@ -2,6 +2,7 @@
 #include <linux/notifier.h>
 #include <linux/socket.h>
 #include <linux/kernel.h>
+#include <linux/export.h>
 #include <net/net_namespace.h>
 #include <net/fib_notifier.h>
 #include <net/netns/ipv4.h>
@@ -49,6 +50,7 @@ static const struct fib_notifier_ops fib4_notifier_ops_template = {
 	.family		= AF_INET,
 	.fib_seq_read	= fib4_seq_read,
 	.fib_dump	= fib4_dump,
+	.owner		= THIS_MODULE,
 };
 
 int __net_init fib4_notifier_init(struct net *net)