l2tp: hold reference on tunnels in netlink dumps

l2tp_tunnel_find_nth() is unsafe: no reference is held on the returned
tunnel, therefore it can be freed whenever the caller uses it.
This patch defines l2tp_tunnel_get_nth() which works similarly, but
also takes a reference on the returned tunnel. The caller then has to
drop it after it stops using the tunnel.

Convert netlink dumps to make them safe against concurrent tunnel
deletion.

Fixes: 309795f4bec2 ("l2tp: Add netlink control API for L2TP")
Signed-off-by: Guillaume Nault <g.nault@alphalink.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index 0fbd3ee26165dd1c9d8304a7d31cd31a3d247f41..c8c4183f0f379dc74a66542e124456047e7db32b 100644 (file)
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -183,6 +183,26 @@ struct l2tp_tunnel *l2tp_tunnel_get(const struct net *net, u32 tunnel_id)
 }
 EXPORT_SYMBOL_GPL(l2tp_tunnel_get);
 
+struct l2tp_tunnel *l2tp_tunnel_get_nth(const struct net *net, int nth)
+{
+       const struct l2tp_net *pn = l2tp_pernet(net);
+       struct l2tp_tunnel *tunnel;
+       int count = 0;
+
+       rcu_read_lock_bh();
+       list_for_each_entry_rcu(tunnel, &pn->l2tp_tunnel_list, list) {
+               if (++count > nth) {
+                       l2tp_tunnel_inc_refcount(tunnel);
+                       rcu_read_unlock_bh();
+                       return tunnel;
+               }
+       }
+       rcu_read_unlock_bh();
+
+       return NULL;
+}
+EXPORT_SYMBOL_GPL(l2tp_tunnel_get_nth);
+
 /* Lookup a session. A new reference is held on the returned session. */
 struct l2tp_session *l2tp_session_get(const struct net *net,
                                      struct l2tp_tunnel *tunnel,

diff --git a/net/l2tp/l2tp_core.h b/net/l2tp/l2tp_core.h
index ba33cbec71eb2e5dca3cbeb4c3dd93239a12949b..e4896413b2b6334b4e7b785d2144728664aa9749 100644 (file)
--- a/net/l2tp/l2tp_core.h
+++ b/net/l2tp/l2tp_core.h
@@ -212,6 +212,8 @@ static inline void *l2tp_session_priv(struct l2tp_session *session)
 }
 
 struct l2tp_tunnel *l2tp_tunnel_get(const struct net *net, u32 tunnel_id);
+struct l2tp_tunnel *l2tp_tunnel_get_nth(const struct net *net, int nth);
+
 void l2tp_tunnel_free(struct l2tp_tunnel *tunnel);
 
 struct l2tp_session *l2tp_session_get(const struct net *net,

diff --git a/net/l2tp/l2tp_netlink.c b/net/l2tp/l2tp_netlink.c
index b05dbd9ffcb2b1fea951b724e51ad2a16a265102..6616c9fd292f1ddae6b974bb2d70de7d7dc1bd28 100644 (file)
--- a/net/l2tp/l2tp_netlink.c
+++ b/net/l2tp/l2tp_netlink.c
@@ -487,14 +487,17 @@ static int l2tp_nl_cmd_tunnel_dump(struct sk_buff *skb, struct netlink_callback
        struct net *net = sock_net(skb->sk);
 
        for (;;) {
-               tunnel = l2tp_tunnel_find_nth(net, ti);
+               tunnel = l2tp_tunnel_get_nth(net, ti);
                if (tunnel == NULL)
                        goto out;
 
                if (l2tp_nl_tunnel_send(skb, NETLINK_CB(cb->skb).portid,
                                        cb->nlh->nlmsg_seq, NLM_F_MULTI,
-                                       tunnel, L2TP_CMD_TUNNEL_GET) < 0)
+                                       tunnel, L2TP_CMD_TUNNEL_GET) < 0) {
+                       l2tp_tunnel_dec_refcount(tunnel);
                        goto out;
+               }
+               l2tp_tunnel_dec_refcount(tunnel);
 
                ti++;
        }
@@ -848,7 +851,7 @@ static int l2tp_nl_cmd_session_dump(struct sk_buff *skb, struct netlink_callback
 
        for (;;) {
                if (tunnel == NULL) {
-                       tunnel = l2tp_tunnel_find_nth(net, ti);
+                       tunnel = l2tp_tunnel_get_nth(net, ti);
                        if (tunnel == NULL)
                                goto out;
                }
@@ -856,6 +859,7 @@ static int l2tp_nl_cmd_session_dump(struct sk_buff *skb, struct netlink_callback
                session = l2tp_session_get_nth(tunnel, si);
                if (session == NULL) {
                        ti++;
+                       l2tp_tunnel_dec_refcount(tunnel);
                        tunnel = NULL;
                        si = 0;
                        continue;
@@ -865,6 +869,7 @@ static int l2tp_nl_cmd_session_dump(struct sk_buff *skb, struct netlink_callback
                                         cb->nlh->nlmsg_seq, NLM_F_MULTI,
                                         session, L2TP_CMD_SESSION_GET) < 0) {
                        l2tp_session_dec_refcount(session);
+                       l2tp_tunnel_dec_refcount(tunnel);
                        break;
                }
                l2tp_session_dec_refcount(session);