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: 04b1d4e50e82 ("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;
 };
 

net/core/fib_notifier.c

@@ -2,6 +2,7 @@
 #include <linux/notifier.h>
 #include <linux/rcupdate.h>
 #include <linux/kernel.h>
+#include <linux/module.h>
 #include <linux/init.h>
 #include <net/net_namespace.h>
 #include <net/fib_notifier.h>
@@ -33,8 +34,12 @@ static unsigned int fib_seq_sum(void)
 
 	rtnl_lock();
 	for_each_net(net) {
-		list_for_each_entry(ops, &net->fib_notifier_ops, list)
+		list_for_each_entry(ops, &net->fib_notifier_ops, list) {
+			if (!try_module_get(ops->owner))
+				continue;
 			fib_seq += ops->fib_seq_read(net);
+			module_put(ops->owner);
+		}
 	}
 	rtnl_unlock();
 
@@ -46,8 +51,12 @@ static int fib_net_dump(struct net *net, struct notifier_block *nb)
 	struct fib_notifier_ops *ops;
 
 	list_for_each_entry_rcu(ops, &net->fib_notifier_ops, list) {
-		int err = ops->fib_dump(net, nb);
+		int err;
 
+		if (!try_module_get(ops->owner))
+			continue;
+		err = ops->fib_dump(net, nb);
+		module_put(ops->owner);
 		if (err)
 			return err;
 	}

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)

net/ipv6/fib6_notifier.c

@@ -1,6 +1,7 @@
 #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/ipv6.h>
@@ -41,6 +42,7 @@ static const struct fib_notifier_ops fib6_notifier_ops_template = {
 	.family		= AF_INET6,
 	.fib_seq_read	= fib6_seq_read,
 	.fib_dump	= fib6_dump,
+	.owner		= THIS_MODULE,
 };
 
 int __net_init fib6_notifier_init(struct net *net)