l2tp: fix potential rcu race (1769192a) · Commits · 戴 / test

While trying to remove useless synchronize_rcu() calls, I found l2tp is indeed incorrectly using two of such calls, but also bumps tunnel refcount after list insertion. tunnel refcount must be incremented before being made publically visible by rcu readers. This fix can be applied to 2.6.35+ and might need a backport for older kernels, since things were shuffled in commit (l2tp: Split pppol2tp patch into separate l2tp and ppp parts) Signed-off-by:

Eric Dumazet <eric.dumazet@gmail.com> CC: Paul E. McKenney <paulmck@linux.vnet.ibm.com> CC: James Chapman <jchapman@katalix.com> Reviewed-by:

Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by:

David S. Miller <davem@davemloft.net>

net/l2tp/l2tp_core.c

+4 −6

Original line number	Diff line number	Diff line
		@@ -1435,16 +1435,15 @@ int l2tp_tunnel_create(struct net *net, int fd, int version, u32 tunnel_id, u32

		/* Add tunnel to our list */
		INIT_LIST_HEAD(&tunnel->list);
		spin_lock_bh(&pn->l2tp_tunnel_list_lock);
		list_add_rcu(&tunnel->list, &pn->l2tp_tunnel_list);
		spin_unlock_bh(&pn->l2tp_tunnel_list_lock);
		synchronize_rcu();
		atomic_inc(&l2tp_tunnel_count);

		/* Bump the reference count. The tunnel context is deleted
		* only when this drops to zero.
		* only when this drops to zero. Must be done before list insertion
		*/
		l2tp_tunnel_inc_refcount(tunnel);
		spin_lock_bh(&pn->l2tp_tunnel_list_lock);
		list_add_rcu(&tunnel->list, &pn->l2tp_tunnel_list);
		spin_unlock_bh(&pn->l2tp_tunnel_list_lock);

		err = 0;
		err:
		@@ -1636,7 +1635,6 @@ struct l2tp_session l2tp_session_create(int priv_size, struct l2tp_tunnel tunn
		hlist_add_head_rcu(&session->global_hlist,
		l2tp_session_id_hash_2(pn, session_id));
		spin_unlock_bh(&pn->l2tp_session_hlist_lock);
		synchronize_rcu();
		}

		/* Ignore management session in session count value */

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