Commit 2dce224f authored by Guillaume Nault's avatar Guillaume Nault Committed by David S. Miller
Browse files

netns: protect netns ID lookups with RCU 



__peernet2id() can be protected by RCU as it only calls idr_for_each(),
which is RCU-safe, and never modifies the nsid table.

rtnl_net_dumpid() can also do lockless lookups. It does two nested
idr_for_each() calls on nsid tables (one direct call and one indirect
call because of rtnl_net_dumpid_one() calling __peernet2id()). The
netnsid tables are never updated. Therefore it is safe to not take the
nsid_lock and run within an RCU-critical section instead.

Signed-off-by: default avatarGuillaume Nault <gnault@redhat.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 49052941

net/core/net_namespace.c

+7 −15
Original line number Diff line number Diff line
@@ -211,7 +211,7 @@ static int net_eq_idr(int id, void *net, void *peer) 
	return 0;

}



/* Should be called with nsid_lock held. */

/* Must be called from RCU-critical section or with nsid_lock held */

static int __peernet2id(const struct net *net, struct net *peer)

{

	int id = idr_for_each(&net->netns_ids, net_eq_idr, peer);
@@ -272,9 +272,10 @@ int peernet2id(struct net *net, struct net *peer) 
{

	int id;



	spin_lock_bh(&net->nsid_lock);

	rcu_read_lock();

	id = __peernet2id(net, peer);

	spin_unlock_bh(&net->nsid_lock);

	rcu_read_unlock();



	return id;

}

EXPORT_SYMBOL(peernet2id);
@@ -941,6 +942,7 @@ struct rtnl_net_dump_cb { 
	int s_idx;

};



/* Runs in RCU-critical section. */

static int rtnl_net_dumpid_one(int id, void *peer, void *data)

{

	struct rtnl_net_dump_cb *net_cb = (struct rtnl_net_dump_cb *)data;
@@ -1025,19 +1027,9 @@ static int rtnl_net_dumpid(struct sk_buff *skb, struct netlink_callback *cb) 
			goto end;

	}



	spin_lock_bh(&net_cb.tgt_net->nsid_lock);

	if (net_cb.fillargs.add_ref &&

	    !net_eq(net_cb.ref_net, net_cb.tgt_net) &&

	    !spin_trylock_bh(&net_cb.ref_net->nsid_lock)) {

		spin_unlock_bh(&net_cb.tgt_net->nsid_lock);

		err = -EAGAIN;

		goto end;

	}

	rcu_read_lock();

	idr_for_each(&net_cb.tgt_net->netns_ids, rtnl_net_dumpid_one, &net_cb);

	if (net_cb.fillargs.add_ref &&

	    !net_eq(net_cb.ref_net, net_cb.tgt_net))

		spin_unlock_bh(&net_cb.ref_net->nsid_lock);

	spin_unlock_bh(&net_cb.tgt_net->nsid_lock);

	rcu_read_unlock();



	cb->args[0] = net_cb.idx;

end:

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