Commit 6b57ff21 authored by Kuniyuki Iwashima's avatar Kuniyuki Iwashima Committed by Jakub Kicinski
Browse files

rtnetlink: Protect link_ops by mutex. 



rtnl_link_unregister() holds RTNL and calls synchronize_srcu(),
but rtnl_newlink() will acquire SRCU frist and then RTNL.

Then, we need to unlink ops and call synchronize_srcu() outside
of RTNL to avoid the deadlock.

   rtnl_link_unregister()       rtnl_newlink()
   ----                         ----
   lock(rtnl_mutex);
                                lock(&ops->srcu);
                                lock(rtnl_mutex);
   sync(&ops->srcu);

Let's move as such and add a mutex to protect link_ops.

Now, link_ops is protected by its dedicated mutex and
rtnl_link_register() no longer needs to hold RTNL.

While at it, we move the initialisation of ops->dellink and
ops->srcu out of the mutex scope.

Signed-off-by: default avatarKuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20241108004823.29419-3-kuniyu@amazon.com


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent d5ec8d91

include/net/rtnetlink.h

+1 −1
Original line number Diff line number Diff line
@@ -71,7 +71,7 @@ static inline int rtnl_msg_family(const struct nlmsghdr *nlh) 
/**

 *	struct rtnl_link_ops - rtnetlink link operations

 *

 *	@list: Used internally, protected by RTNL and SRCU

 *	@list: Used internally, protected by link_ops_mutex and SRCU

 *	@srcu: Used internally

 *	@kind: Identifier

 *	@netns_refund: Physical device, move to init_net on netns exit

net/core/rtnetlink.c

+20 −13
Original line number Diff line number Diff line
@@ -466,6 +466,7 @@ void __rtnl_unregister_many(const struct rtnl_msg_handler *handlers, int n) 
}

EXPORT_SYMBOL_GPL(__rtnl_unregister_many);



static DEFINE_MUTEX(link_ops_mutex);

static LIST_HEAD(link_ops);



static struct rtnl_link_ops *rtnl_link_ops_get(const char *kind, int *srcu_index)
@@ -508,14 +509,6 @@ int __rtnl_link_register(struct rtnl_link_ops *ops) 
	struct rtnl_link_ops *tmp;

	int err;



	/* When RTNL is removed, add lock for link_ops. */

	ASSERT_RTNL();



	list_for_each_entry(tmp, &link_ops, list) {

		if (!strcmp(ops->kind, tmp->kind))

			return -EEXIST;

	}



	/* The check for alloc/setup is here because if ops

	 * does not have that filled up, it is not possible

	 * to use the ops for creating device. So do not
@@ -528,9 +521,20 @@ int __rtnl_link_register(struct rtnl_link_ops *ops) 
	if (err)

		return err;



	mutex_lock(&link_ops_mutex);



	list_for_each_entry(tmp, &link_ops, list) {

		if (!strcmp(ops->kind, tmp->kind)) {

			err = -EEXIST;

			goto unlock;

		}

	}



	list_add_tail_rcu(&ops->list, &link_ops);

unlock:

	mutex_unlock(&link_ops_mutex);



	return 0;

	return err;

}

EXPORT_SYMBOL_GPL(__rtnl_link_register);
@@ -598,14 +602,17 @@ void rtnl_link_unregister(struct rtnl_link_ops *ops) 
{

	struct net *net;



	/* Close the race with setup_net() and cleanup_net() */

	down_write(&pernet_ops_rwsem);

	rtnl_lock_unregistering_all();



	mutex_lock(&link_ops_mutex);

	list_del_rcu(&ops->list);

	mutex_unlock(&link_ops_mutex);



	synchronize_srcu(&ops->srcu);

	cleanup_srcu_struct(&ops->srcu);



	/* Close the race with setup_net() and cleanup_net() */

	down_write(&pernet_ops_rwsem);

	rtnl_lock_unregistering_all();



	for_each_net(net)

		__rtnl_kill_links(net, ops);