l2tp: take reference on sessions being dumped

commit e08293a4ccbcc993ded0fdc46f1e57926b833d63 upstream.

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>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index 8ce9cb489df1ff57b359c2e5063018452a8b3995..3954b18f42ee98d5c69a2e13c647e6fe56e1900e 100644 (file)
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -275,7 +275,8 @@ struct l2tp_session *l2tp_session_get(struct net *net,
 }
 EXPORT_SYMBOL_GPL(l2tp_session_get);
 
-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 hlist_node *walk;
@@ -286,6 +287,9 @@ 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, walk, &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;
                        }
@@ -296,7 +300,7 @@ 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 522d6aa2a4a64718090c84c2c4974381aba2ab64..1caf21e1182259670a9e756c2bc91e78651f8176 100644 (file)
--- a/net/l2tp/l2tp_core.h
+++ b/net/l2tp/l2tp_core.h
@@ -226,7 +226,8 @@ struct l2tp_session *l2tp_session_get(struct net *net,
                                      struct l2tp_tunnel *tunnel,
                                      u32 session_id, bool do_ref);
 extern struct l2tp_session *l2tp_session_find(struct net *net, struct l2tp_tunnel *tunnel, u32 session_id);
-extern 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_get_by_ifname(struct net *net, char *ifname,
                                                bool do_ref);
 extern struct l2tp_tunnel *l2tp_tunnel_find(struct net *net, u32 tunnel_id);

diff --git a/net/l2tp/l2tp_debugfs.c b/net/l2tp/l2tp_debugfs.c
index 76130134bfa6215d3cb7ffce9813f95724dc7d65..8bb0d56c822b9c7c0a487a7b30c8be4888326b1d 100644 (file)
--- a/net/l2tp/l2tp_debugfs.c
+++ b/net/l2tp/l2tp_debugfs.c
@@ -51,7 +51,7 @@ 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) {
@@ -227,10 +227,14 @@ 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 2b8048f452fe6ef36cca0077ceaff49e290216da..6fd6322851066d80fc6f13fc4c421c7753a72bbd 100644 (file)
--- a/net/l2tp/l2tp_netlink.c
+++ b/net/l2tp/l2tp_netlink.c
@@ -669,7 +669,7 @@ 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;
@@ -679,8 +679,11 @@ static int l2tp_nl_cmd_session_dump(struct sk_buff *skb, struct netlink_callback
 
                if (l2tp_nl_session_send(skb, NETLINK_CB(cb->skb).pid,
                                         cb->nlh->nlmsg_seq, NLM_F_MULTI,
-                                        session) <= 0)
+                                        session) <= 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 dae5a6d9e160bd19b2a326b2cc6d8715032ee867..c404a6a8dd742c0c30edb17df5a0b59bf1be6ae0 100644 (file)
--- a/net/l2tp/l2tp_ppp.c
+++ b/net/l2tp/l2tp_ppp.c
@@ -1564,7 +1564,7 @@ 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) {
@@ -1691,10 +1691,14 @@ 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;