l2tp: fix race in l2tp_recv_common()
commit 61b9a047729bb230978178bca6729689d0c50ca2 upstream.
Taking a reference on sessions in l2tp_recv_common() is racy; this
has to be done by the callers.
To this end, a new function is required (l2tp_session_get()) to
atomically lookup a session and take a reference on it. Callers then
have to manually drop this reference.
Fixes: fd558d186df2 ("l2tp: Split pppol2tp patch into separate l2tp and ppp parts")
Signed-off-by: Guillaume Nault <g.nault@alphalink.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index e702cb95..046a5ba 100644
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -278,6 +278,55 @@
}
EXPORT_SYMBOL_GPL(l2tp_session_find);
+/* Like l2tp_session_find() but takes a reference on the returned session.
+ * Optionally calls session->ref() too if do_ref is true.
+ */
+struct l2tp_session *l2tp_session_get(struct net *net,
+ struct l2tp_tunnel *tunnel,
+ u32 session_id, bool do_ref)
+{
+ struct hlist_head *session_list;
+ struct l2tp_session *session;
+
+ if (!tunnel) {
+ struct l2tp_net *pn = l2tp_pernet(net);
+
+ session_list = l2tp_session_id_hash_2(pn, session_id);
+
+ rcu_read_lock_bh();
+ hlist_for_each_entry_rcu(session, session_list, global_hlist) {
+ if (session->session_id == session_id) {
+ l2tp_session_inc_refcount(session);
+ if (do_ref && session->ref)
+ session->ref(session);
+ rcu_read_unlock_bh();
+
+ return session;
+ }
+ }
+ rcu_read_unlock_bh();
+
+ return NULL;
+ }
+
+ session_list = l2tp_session_id_hash(tunnel, session_id);
+ read_lock_bh(&tunnel->hlist_lock);
+ hlist_for_each_entry(session, session_list, hlist) {
+ if (session->session_id == session_id) {
+ l2tp_session_inc_refcount(session);
+ if (do_ref && session->ref)
+ session->ref(session);
+ read_unlock_bh(&tunnel->hlist_lock);
+
+ return session;
+ }
+ }
+ read_unlock_bh(&tunnel->hlist_lock);
+
+ return NULL;
+}
+EXPORT_SYMBOL_GPL(l2tp_session_get);
+
struct l2tp_session *l2tp_session_get_nth(struct l2tp_tunnel *tunnel, int nth,
bool do_ref)
{
@@ -637,6 +686,9 @@
* a data (not control) frame before coming here. Fields up to the
* session-id have already been parsed and ptr points to the data
* after the session-id.
+ *
+ * session->ref() must have been called prior to l2tp_recv_common().
+ * session->deref() will be called automatically after skb is processed.
*/
void l2tp_recv_common(struct l2tp_session *session, struct sk_buff *skb,
unsigned char *ptr, unsigned char *optr, u16 hdrflags,
@@ -646,14 +698,6 @@
int offset;
u32 ns, nr;
- /* The ref count is increased since we now hold a pointer to
- * the session. Take care to decrement the refcnt when exiting
- * this function from now on...
- */
- l2tp_session_inc_refcount(session);
- if (session->ref)
- (*session->ref)(session);
-
/* Parse and check optional cookie */
if (session->peer_cookie_len > 0) {
if (memcmp(ptr, &session->peer_cookie[0], session->peer_cookie_len)) {
@@ -806,8 +850,6 @@
/* Try to dequeue as many skbs from reorder_q as we can. */
l2tp_recv_dequeue(session);
- l2tp_session_dec_refcount(session);
-
return;
discard:
@@ -816,8 +858,6 @@
if (session->deref)
(*session->deref)(session);
-
- l2tp_session_dec_refcount(session);
}
EXPORT_SYMBOL(l2tp_recv_common);
@@ -924,8 +964,14 @@
}
/* Find the session context */
- session = l2tp_session_find(tunnel->l2tp_net, tunnel, session_id);
+ session = l2tp_session_get(tunnel->l2tp_net, tunnel, session_id, true);
if (!session || !session->recv_skb) {
+ if (session) {
+ if (session->deref)
+ session->deref(session);
+ l2tp_session_dec_refcount(session);
+ }
+
/* Not found? Pass to userspace to deal with */
l2tp_info(tunnel, L2TP_MSG_DATA,
"%s: no session found (%u/%u). Passing up.\n",
@@ -934,6 +980,7 @@
}
l2tp_recv_common(session, skb, ptr, optr, hdrflags, length, payload_hook);
+ l2tp_session_dec_refcount(session);
return 0;