Commit 54652eb1 authored by Guillaume Nault's avatar Guillaume Nault Committed by David S. Miller
Browse files

l2tp: hold tunnel while looking up sessions in l2tp_netlink 



l2tp_tunnel_find() doesn't take a reference on the returned tunnel.
Therefore, it's unsafe to use it because the returned tunnel can go
away on us anytime.

Fix this by defining l2tp_tunnel_get(), which works like
l2tp_tunnel_find(), but takes a reference on the returned tunnel.
Caller then has to drop this reference using l2tp_tunnel_dec_refcount().

As l2tp_tunnel_dec_refcount() needs to be moved to l2tp_core.h, let's
simplify the patch and not move the L2TP_REFCNT_DEBUG part. This code
has been broken (not even compiling) in May 2012 by
commit a4ca44fa ("net: l2tp: Standardize logging styles")
and fixed more than two years later by
commit 29abe2fd ("l2tp: fix missing line continuation"). So it
doesn't appear to be used by anyone.

Same thing for l2tp_tunnel_free(); instead of moving it to l2tp_core.h,
let's just simplify things and call kfree_rcu() directly in
l2tp_tunnel_dec_refcount(). Extra assertions and debugging code
provided by l2tp_tunnel_free() didn't help catching any of the
reference counting and socket handling issues found while working on
this series.

Fixes: 309795f4 ("l2tp: Add netlink control API for L2TP")
Signed-off-by: default avatarGuillaume Nault <g.nault@alphalink.fr>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 9ee369a4

net/l2tp/l2tp_core.c

+21 −45
Original line number Diff line number Diff line
@@ -113,7 +113,6 @@ struct l2tp_net { 
	spinlock_t l2tp_session_hlist_lock;

};



static void l2tp_tunnel_free(struct l2tp_tunnel *tunnel);



static inline struct l2tp_tunnel *l2tp_tunnel(struct sock *sk)

{
@@ -127,39 +126,6 @@ static inline struct l2tp_net *l2tp_pernet(const struct net *net) 
	return net_generic(net, l2tp_net_id);

}



/* Tunnel reference counts. Incremented per session that is added to

 * the tunnel.

 */

static inline void l2tp_tunnel_inc_refcount_1(struct l2tp_tunnel *tunnel)

{

	refcount_inc(&tunnel->ref_count);

}



static inline void l2tp_tunnel_dec_refcount_1(struct l2tp_tunnel *tunnel)

{

	if (refcount_dec_and_test(&tunnel->ref_count))

		l2tp_tunnel_free(tunnel);

}

#ifdef L2TP_REFCNT_DEBUG

#define l2tp_tunnel_inc_refcount(_t)					\

do {									\

	pr_debug("l2tp_tunnel_inc_refcount: %s:%d %s: cnt=%d\n",	\

		 __func__, __LINE__, (_t)->name,			\

		 refcount_read(&_t->ref_count));			\

	l2tp_tunnel_inc_refcount_1(_t);					\

} while (0)

#define l2tp_tunnel_dec_refcount(_t)					\

do {									\

	pr_debug("l2tp_tunnel_dec_refcount: %s:%d %s: cnt=%d\n",	\

		 __func__, __LINE__, (_t)->name,			\

		 refcount_read(&_t->ref_count));			\

	l2tp_tunnel_dec_refcount_1(_t);					\

} while (0)

#else

#define l2tp_tunnel_inc_refcount(t) l2tp_tunnel_inc_refcount_1(t)

#define l2tp_tunnel_dec_refcount(t) l2tp_tunnel_dec_refcount_1(t)

#endif



/* Session hash global list for L2TPv3.

 * The session_id SHOULD be random according to RFC3931, but several

 * L2TP implementations use incrementing session_ids.  So we do a real
@@ -229,6 +195,27 @@ l2tp_session_id_hash(struct l2tp_tunnel *tunnel, u32 session_id) 
	return &tunnel->session_hlist[hash_32(session_id, L2TP_HASH_BITS)];

}



/* Lookup a tunnel. A new reference is held on the returned tunnel. */

struct l2tp_tunnel *l2tp_tunnel_get(const struct net *net, u32 tunnel_id)

{

	const struct l2tp_net *pn = l2tp_pernet(net);

	struct l2tp_tunnel *tunnel;



	rcu_read_lock_bh();

	list_for_each_entry_rcu(tunnel, &pn->l2tp_tunnel_list, list) {

		if (tunnel->tunnel_id == tunnel_id) {

			l2tp_tunnel_inc_refcount(tunnel);

			rcu_read_unlock_bh();



			return tunnel;

		}

	}

	rcu_read_unlock_bh();



	return NULL;

}

EXPORT_SYMBOL_GPL(l2tp_tunnel_get);



/* Lookup a session. A new reference is held on the returned session.

 * Optionally calls session->ref() too if do_ref is true.

 */
@@ -1348,17 +1335,6 @@ static void l2tp_udp_encap_destroy(struct sock *sk) 
	}

}



/* Really kill the tunnel.

 * Come here only when all sessions have been cleared from the tunnel.

 */

static void l2tp_tunnel_free(struct l2tp_tunnel *tunnel)

{

	BUG_ON(refcount_read(&tunnel->ref_count) != 0);

	BUG_ON(tunnel->sock != NULL);

	l2tp_info(tunnel, L2TP_MSG_CONTROL, "%s: free...\n", tunnel->name);

	kfree_rcu(tunnel, rcu);

}



/* Workqueue tunnel deletion function */

static void l2tp_tunnel_del_work(struct work_struct *work)

{

net/l2tp/l2tp_core.h

+13 −0
Original line number Diff line number Diff line
@@ -231,6 +231,8 @@ out: 
	return tunnel;

}



struct l2tp_tunnel *l2tp_tunnel_get(const struct net *net, u32 tunnel_id);



struct l2tp_session *l2tp_session_get(const struct net *net,

				      struct l2tp_tunnel *tunnel,

				      u32 session_id, bool do_ref);
@@ -269,6 +271,17 @@ int l2tp_nl_register_ops(enum l2tp_pwtype pw_type, 
void l2tp_nl_unregister_ops(enum l2tp_pwtype pw_type);

int l2tp_ioctl(struct sock *sk, int cmd, unsigned long arg);



static inline void l2tp_tunnel_inc_refcount(struct l2tp_tunnel *tunnel)

{

	refcount_inc(&tunnel->ref_count);

}



static inline void l2tp_tunnel_dec_refcount(struct l2tp_tunnel *tunnel)

{

	if (refcount_dec_and_test(&tunnel->ref_count))

		kfree_rcu(tunnel, rcu);

}



/* Session reference counts. Incremented when code obtains a reference

 * to a session.

 */

net/l2tp/l2tp_netlink.c

+4 −2
Original line number Diff line number Diff line
@@ -65,10 +65,12 @@ static struct l2tp_session *l2tp_nl_session_get(struct genl_info *info, 
		   (info->attrs[L2TP_ATTR_CONN_ID])) {

		tunnel_id = nla_get_u32(info->attrs[L2TP_ATTR_CONN_ID]);

		session_id = nla_get_u32(info->attrs[L2TP_ATTR_SESSION_ID]);

		tunnel = l2tp_tunnel_find(net, tunnel_id);

		if (tunnel)

		tunnel = l2tp_tunnel_get(net, tunnel_id);

		if (tunnel) {

			session = l2tp_session_get(net, tunnel, session_id,

						   do_ref);

			l2tp_tunnel_dec_refcount(tunnel);

		}

	}



	return session;

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