l2tp: purge socket queues in the .destruct() callback

[ Upstream commit e91793bb615cf6cdd59c0b6749fe173687bb0947 ]

The Rx path may grab the socket right before pppol2tp_release(), but
nothing guarantees that it will enqueue packets before
skb_queue_purge(). Therefore, the socket can be destroyed without its
queues fully purged.

Fix this by purging queues in pppol2tp_session_destruct() where we're
guaranteed nothing is still referencing the socket.

Fixes: 9e9cb6221aa7 ("l2tp: fix userspace reception on plain L2TP sockets")
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>

1 files changed, 4 insertions, 3 deletions

diff --git a/net/l2tp/l2tp_ppp.c b/net/l2tp/l2tp_ppp.c
index 41d47bfda15c..51c190dc2582 100644
--- a/net/l2tp/l2tp_ppp.c
+++ b/net/l2tp/l2tp_ppp.c
@@ -450,6 +450,10 @@ static void pppol2tp_session_close(struct l2tp_session *session)
 static void pppol2tp_session_destruct(struct sock *sk)
 {
         struct l2tp_session *session = sk->sk_user_data;
+
+        skb_queue_purge(&sk->sk_receive_queue);
+        skb_queue_purge(&sk->sk_write_queue);
+
         if (session) {
                 sk->sk_user_data = NULL;
                 BUG_ON(session->magic != L2TP_SESSION_MAGIC);
@@ -488,9 +492,6 @@ static int pppol2tp_release(struct socket *sock)
                 l2tp_session_queue_purge(session);
                 sock_put(sk);
         }
-        skb_queue_purge(&sk->sk_receive_queue);
-        skb_queue_purge(&sk->sk_write_queue);
-
         release_sock(sk);
 
         /* This will delete the session context via