l2tp: take reference on sessions being dumped

BugLink: http://bugs.launchpad.net/bugs/1688499
[ Upstream commit e08293a4ccbcc993ded0fdc46f1e57926b833d63 ]

Take a reference on the sessions returned by l2tp_session_find_nth()
(and rename it l2tp_session_get_nth() to reflect this change), so that
caller is assured that the session isn't going to disappear while
processing it.

For procfs and debugfs handlers, the session is held in the .start()
callback and dropped in .show(). Given that pppol2tp_seq_session_show()
dereferences the associated PPPoL2TP socket and that
l2tp_dfs_seq_session_show() might call pppol2tp_show(), we also need to
call the session's .ref() callback to prevent the socket from going
away from under us.

Fixes: fd558d186df2 ("l2tp: Split pppol2tp patch into separate l2tp and ppp parts")
Fixes: 0ad6614048cf ("l2tp: Add debugfs files for dumping l2tp debug info")
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index 85948c69b23681ef9542e43faad8af235a309828..56036ab5dcb7719b640cc3bcc731a40a22cc6387 100644 (file)
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -278,7 +278,8 @@ struct l2tp_session *l2tp_session_find(struct net *net, struct l2tp_tunnel *tunn
 }
 EXPORT_SYMBOL_GPL(l2tp_session_find);
 
-struct l2tp_session *l2tp_session_find_nth(struct l2tp_tunnel *tunnel, int nth)
+struct l2tp_session *l2tp_session_get_nth(struct l2tp_tunnel *tunnel, int nth,
+                                         bool do_ref)
 {
        int hash;
        struct l2tp_session *session;
@@ -288,6 +289,9 @@ struct l2tp_session *l2tp_session_find_nth(struct l2tp_tunnel *tunnel, int nth)
        for (hash = 0; hash < L2TP_HASH_SIZE; hash++) {
                hlist_for_each_entry(session, &tunnel->session_hlist[hash], hlist) {
                        if (++count > nth) {
+                               l2tp_session_inc_refcount(session);
+                               if (do_ref && session->ref)
+                                       session->ref(session);
                                read_unlock_bh(&tunnel->hlist_lock);
                                return session;
                        }
@@ -298,7 +302,7 @@ struct l2tp_session *l2tp_session_find_nth(struct l2tp_tunnel *tunnel, int nth)
 
        return NULL;
 }
-EXPORT_SYMBOL_GPL(l2tp_session_find_nth);
+EXPORT_SYMBOL_GPL(l2tp_session_get_nth);
 
 /* Lookup a session by interface name.
  * This is very inefficient but is only used by management interfaces.

diff --git a/net/l2tp/l2tp_core.h b/net/l2tp/l2tp_core.h
index aebf281d09eeb31c531eb624bd2ddd78cab8da9b..221648b07b3cc9e4da9714c29c056ed0969ad90f 100644 (file)
--- a/net/l2tp/l2tp_core.h
+++ b/net/l2tp/l2tp_core.h
@@ -233,7 +233,8 @@ out:
 struct l2tp_session *l2tp_session_find(struct net *net,
                                       struct l2tp_tunnel *tunnel,
                                       u32 session_id);
-struct l2tp_session *l2tp_session_find_nth(struct l2tp_tunnel *tunnel, int nth);
+struct l2tp_session *l2tp_session_get_nth(struct l2tp_tunnel *tunnel, int nth,
+                                         bool do_ref);
 struct l2tp_session *l2tp_session_find_by_ifname(struct net *net, char *ifname);
 struct l2tp_tunnel *l2tp_tunnel_find(struct net *net, u32 tunnel_id);
 struct l2tp_tunnel *l2tp_tunnel_find_nth(struct net *net, int nth);

diff --git a/net/l2tp/l2tp_debugfs.c b/net/l2tp/l2tp_debugfs.c
index 2d6760a2ae347b96d465e30192ab8a7957258d32..d100aed3d06fb63b8851a00c55350f1728b18599 100644 (file)
--- a/net/l2tp/l2tp_debugfs.c
+++ b/net/l2tp/l2tp_debugfs.c
@@ -53,7 +53,7 @@ static void l2tp_dfs_next_tunnel(struct l2tp_dfs_seq_data *pd)
 
 static void l2tp_dfs_next_session(struct l2tp_dfs_seq_data *pd)
 {
-       pd->session = l2tp_session_find_nth(pd->tunnel, pd->session_idx);
+       pd->session = l2tp_session_get_nth(pd->tunnel, pd->session_idx, true);
        pd->session_idx++;
 
        if (pd->session == NULL) {
@@ -238,10 +238,14 @@ static int l2tp_dfs_seq_show(struct seq_file *m, void *v)
        }
 
        /* Show the tunnel or session context */
-       if (pd->session == NULL)
+       if (!pd->session) {
                l2tp_dfs_seq_tunnel_show(m, pd->tunnel);
-       else
+       } else {
                l2tp_dfs_seq_session_show(m, pd->session);
+               if (pd->session->deref)
+                       pd->session->deref(pd->session);
+               l2tp_session_dec_refcount(pd->session);
+       }
 
 out:
        return 0;

diff --git a/net/l2tp/l2tp_netlink.c b/net/l2tp/l2tp_netlink.c
index 3620fba317863dc59c93c1089faf63451e831aa5..ad191a786806d28a3af3754b2a41c911d898593a 100644 (file)
--- a/net/l2tp/l2tp_netlink.c
+++ b/net/l2tp/l2tp_netlink.c
@@ -852,7 +852,7 @@ static int l2tp_nl_cmd_session_dump(struct sk_buff *skb, struct netlink_callback
                                goto out;
                }
 
-               session = l2tp_session_find_nth(tunnel, si);
+               session = l2tp_session_get_nth(tunnel, si, false);
                if (session == NULL) {
                        ti++;
                        tunnel = NULL;
@@ -862,8 +862,11 @@ static int l2tp_nl_cmd_session_dump(struct sk_buff *skb, struct netlink_callback
 
                if (l2tp_nl_session_send(skb, NETLINK_CB(cb->skb).portid,
                                         cb->nlh->nlmsg_seq, NLM_F_MULTI,
-                                        session, L2TP_CMD_SESSION_GET) < 0)
+                                        session, L2TP_CMD_SESSION_GET) < 0) {
+                       l2tp_session_dec_refcount(session);
                        break;
+               }
+               l2tp_session_dec_refcount(session);
 
                si++;
        }

diff --git a/net/l2tp/l2tp_ppp.c b/net/l2tp/l2tp_ppp.c
index 123b6a2411a03832b1b927a6b0eb47d5617f23a1..2f1944c99672ceacc6468c5a6ee542d6054b1b3a 100644 (file)
--- a/net/l2tp/l2tp_ppp.c
+++ b/net/l2tp/l2tp_ppp.c
@@ -1555,7 +1555,7 @@ static void pppol2tp_next_tunnel(struct net *net, struct pppol2tp_seq_data *pd)
 
 static void pppol2tp_next_session(struct net *net, struct pppol2tp_seq_data *pd)
 {
-       pd->session = l2tp_session_find_nth(pd->tunnel, pd->session_idx);
+       pd->session = l2tp_session_get_nth(pd->tunnel, pd->session_idx, true);
        pd->session_idx++;
 
        if (pd->session == NULL) {
@@ -1682,10 +1682,14 @@ static int pppol2tp_seq_show(struct seq_file *m, void *v)
 
        /* Show the tunnel or session context.
         */
-       if (pd->session == NULL)
+       if (!pd->session) {
                pppol2tp_seq_tunnel_show(m, pd->tunnel);
-       else
+       } else {
                pppol2tp_seq_session_show(m, pd->session);
+               if (pd->session->deref)
+                       pd->session->deref(pd->session);
+               l2tp_session_dec_refcount(pd->session);
+       }
 
 out:
        return 0;