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>

include/net/fib_notifier.h

@@ -2,6 +2,7 @@
 #define __NET_FIB_NOTIFIER_H
 
 #include <linux/types.h>
+#include <linux/module.h>
 #include <linux/notifier.h>
 #include <net/net_namespace.h>
 
@@ -26,6 +27,7 @@ struct fib_notifier_ops {
 	struct list_head list;
 	unsigned int (*fib_seq_read)(struct net *net);
 	int (*fib_dump)(struct net *net, struct notifier_block *nb);
+	struct module *owner;
 	struct rcu_head rcu;
 };