Merge branch 'l2tp-tunnel-refs'

Guillaume Nault says:

====================
l2tp: fix some l2tp_tunnel_find() issues in l2tp_netlink

Since l2tp_tunnel_find() doesn't take a reference on the tunnel it
returns, its users are almost guaranteed to be racy.

This series defines l2tp_tunnel_get() which can be used as a safe
replacement, and converts some of l2tp_tunnel_find() users in the
l2tp_netlink module.

Other users often combine this issue with other more or less subtle
races. They will be fixed incrementally in followup series.
====================
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/l2tp/l2tp_core.c

@@ -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

@@ -231,6 +231,8 @@ static inline struct l2tp_tunnel *l2tp_sock_to_tunnel(struct sock *sk)
 	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

@@ -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;
@@ -271,8 +273,8 @@ static int l2tp_nl_cmd_tunnel_delete(struct sk_buff *skb, struct genl_info *info
 	}
 	tunnel_id = nla_get_u32(info->attrs[L2TP_ATTR_CONN_ID]);
 
-	tunnel = l2tp_tunnel_find(net, tunnel_id);
-	if (tunnel == NULL) {
+	tunnel = l2tp_tunnel_get(net, tunnel_id);
+	if (!tunnel) {
 		ret = -ENODEV;
 		goto out;
 	}
@@ -282,6 +284,8 @@ static int l2tp_nl_cmd_tunnel_delete(struct sk_buff *skb, struct genl_info *info
 
 	(void) l2tp_tunnel_delete(tunnel);
 
+	l2tp_tunnel_dec_refcount(tunnel);
+
 out:
 	return ret;
 }
@@ -299,8 +303,8 @@ static int l2tp_nl_cmd_tunnel_modify(struct sk_buff *skb, struct genl_info *info
 	}
 	tunnel_id = nla_get_u32(info->attrs[L2TP_ATTR_CONN_ID]);
 
-	tunnel = l2tp_tunnel_find(net, tunnel_id);
-	if (tunnel == NULL) {
+	tunnel = l2tp_tunnel_get(net, tunnel_id);
+	if (!tunnel) {
 		ret = -ENODEV;
 		goto out;
 	}
@@ -311,6 +315,8 @@ static int l2tp_nl_cmd_tunnel_modify(struct sk_buff *skb, struct genl_info *info
 	ret = l2tp_tunnel_notify(&l2tp_nl_family, info,
 				 tunnel, L2TP_CMD_TUNNEL_MODIFY);
 
+	l2tp_tunnel_dec_refcount(tunnel);
+
 out:
 	return ret;
 }
@@ -438,34 +444,37 @@ static int l2tp_nl_cmd_tunnel_get(struct sk_buff *skb, struct genl_info *info)
 
 	if (!info->attrs[L2TP_ATTR_CONN_ID]) {
 		ret = -EINVAL;
-		goto out;
+		goto err;
 	}
 
 	tunnel_id = nla_get_u32(info->attrs[L2TP_ATTR_CONN_ID]);
 
-	tunnel = l2tp_tunnel_find(net, tunnel_id);
-	if (tunnel == NULL) {
-		ret = -ENODEV;
-		goto out;
-	}
-
 	msg = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_KERNEL);
 	if (!msg) {
 		ret = -ENOMEM;
-		goto out;
+		goto err;
+	}
+
+	tunnel = l2tp_tunnel_get(net, tunnel_id);
+	if (!tunnel) {
+		ret = -ENODEV;
+		goto err_nlmsg;
 	}
 
 	ret = l2tp_nl_tunnel_send(msg, info->snd_portid, info->snd_seq,
 				  NLM_F_ACK, tunnel, L2TP_CMD_TUNNEL_GET);
 	if (ret < 0)
-		goto err_out;
+		goto err_nlmsg_tunnel;
+
+	l2tp_tunnel_dec_refcount(tunnel);
 
 	return genlmsg_unicast(net, msg, info->snd_portid);
 
-err_out:
+err_nlmsg_tunnel:
+	l2tp_tunnel_dec_refcount(tunnel);
+err_nlmsg:
 	nlmsg_free(msg);
-
-out:
+err:
 	return ret;
 }
 
@@ -509,8 +518,9 @@ static int l2tp_nl_cmd_session_create(struct sk_buff *skb, struct genl_info *inf
 		ret = -EINVAL;
 		goto out;
 	}
+
 	tunnel_id = nla_get_u32(info->attrs[L2TP_ATTR_CONN_ID]);
-	tunnel = l2tp_tunnel_find(net, tunnel_id);
+	tunnel = l2tp_tunnel_get(net, tunnel_id);
 	if (!tunnel) {
 		ret = -ENODEV;
 		goto out;
@@ -518,24 +528,24 @@ static int l2tp_nl_cmd_session_create(struct sk_buff *skb, struct genl_info *inf
 
 	if (!info->attrs[L2TP_ATTR_SESSION_ID]) {
 		ret = -EINVAL;
-		goto out;
+		goto out_tunnel;
 	}
 	session_id = nla_get_u32(info->attrs[L2TP_ATTR_SESSION_ID]);
 
 	if (!info->attrs[L2TP_ATTR_PEER_SESSION_ID]) {
 		ret = -EINVAL;
-		goto out;
+		goto out_tunnel;
 	}
 	peer_session_id = nla_get_u32(info->attrs[L2TP_ATTR_PEER_SESSION_ID]);
 
 	if (!info->attrs[L2TP_ATTR_PW_TYPE]) {
 		ret = -EINVAL;
-		goto out;
+		goto out_tunnel;
 	}
 	cfg.pw_type = nla_get_u16(info->attrs[L2TP_ATTR_PW_TYPE]);
 	if (cfg.pw_type >= __L2TP_PWTYPE_MAX) {
 		ret = -EINVAL;
-		goto out;
+		goto out_tunnel;
 	}
 
 	if (tunnel->version > 2) {
@@ -557,7 +567,7 @@ static int l2tp_nl_cmd_session_create(struct sk_buff *skb, struct genl_info *inf
 			u16 len = nla_len(info->attrs[L2TP_ATTR_COOKIE]);
 			if (len > 8) {
 				ret = -EINVAL;
-				goto out;
+				goto out_tunnel;
 			}
 			cfg.cookie_len = len;
 			memcpy(&cfg.cookie[0], nla_data(info->attrs[L2TP_ATTR_COOKIE]), len);
@@ -566,7 +576,7 @@ static int l2tp_nl_cmd_session_create(struct sk_buff *skb, struct genl_info *inf
 			u16 len = nla_len(info->attrs[L2TP_ATTR_PEER_COOKIE]);
 			if (len > 8) {
 				ret = -EINVAL;
-				goto out;
+				goto out_tunnel;
 			}
 			cfg.peer_cookie_len = len;
 			memcpy(&cfg.peer_cookie[0], nla_data(info->attrs[L2TP_ATTR_PEER_COOKIE]), len);
@@ -609,7 +619,7 @@ static int l2tp_nl_cmd_session_create(struct sk_buff *skb, struct genl_info *inf
 	if ((l2tp_nl_cmd_ops[cfg.pw_type] == NULL) ||
 	    (l2tp_nl_cmd_ops[cfg.pw_type]->session_create == NULL)) {
 		ret = -EPROTONOSUPPORT;
-		goto out;
+		goto out_tunnel;
 	}
 
 	/* Check that pseudowire-specific params are present */
@@ -619,7 +629,7 @@ static int l2tp_nl_cmd_session_create(struct sk_buff *skb, struct genl_info *inf
 	case L2TP_PWTYPE_ETH_VLAN:
 		if (!info->attrs[L2TP_ATTR_VLAN_ID]) {
 			ret = -EINVAL;
-			goto out;
+			goto out_tunnel;
 		}
 		break;
 	case L2TP_PWTYPE_ETH:
@@ -647,6 +657,8 @@ static int l2tp_nl_cmd_session_create(struct sk_buff *skb, struct genl_info *inf
 		}
 	}
 
+out_tunnel:
+	l2tp_tunnel_dec_refcount(tunnel);
 out:
 	return ret;
 }