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 3.16: 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 7f2e5fc95966554568d9986dc485b67def82a2dd..384d92ecd26a2b9c67b73fc02c07920141f4b26e 100644 (file)
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -326,7 +326,8 @@ 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 l2tp_session *session;
@@ -336,6 +337,9 @@ 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;
                        }
@@ -346,7 +350,7 @@ 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 8d5f70dc9f70cc2a93309360f816d9f581b17821..12b08016a3125616d502317d7f3f8625770819cc 100644 (file)
--- a/net/l2tp/l2tp_core.h
+++ b/net/l2tp/l2tp_core.h
@@ -246,7 +246,8 @@ struct l2tp_session *l2tp_session_get(struct net *net,
 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_get_by_ifname(struct net *net, char *ifname,
                                                bool do_ref);
 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 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 87cbf877da2b598feb1b0bb6d49eaa94d12f2f4c..a492a781ce9e1cefee8475cd8f5969fd7d24b7dc 100644 (file)
--- a/net/l2tp/l2tp_netlink.c
+++ b/net/l2tp/l2tp_netlink.c
@@ -740,7 +740,7 @@ 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;
@@ -750,8 +750,11 @@ 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) <= 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 09ba87450a30ff1cd5291ef127a0b6a96c307c82..df1538ce73014cb0d7a942d90b7e9d3a305183ee 100644 (file)
--- a/net/l2tp/l2tp_ppp.c
+++ b/net/l2tp/l2tp_ppp.c
@@ -1579,7 +1579,7 @@ 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) {
@@ -1706,10 +1706,14 @@ 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;