ovpn: ensure socket is owned by ovpn before deref sk_user_data

Some subsystems, like BPF SOCKMAP, set sk_user_data without
actually setting the encap_type.

For this reason, we must make sure that the type is the
one ovpn expects before dereferencing sk_user_data.

Failing to do so may lead to out-of-bounds reads.

Fixes: f6226ae7a0cd ("ovpn: introduce the ovpn_socket object")
Signed-off-by: Antonio Quartulli <antonio@openvpn.net>

diff --git a/drivers/net/ovpn/socket.c b/drivers/net/ovpn/socket.c
index 517caa64a4fef75d7adb2c49a0fdf2f9045c383a..6cbeb2caaeecaad26dc8e93ac6837dcaa93b8943 100644 (file)
--- a/drivers/net/ovpn/socket.c
+++ b/drivers/net/ovpn/socket.c
@@ -162,6 +162,15 @@ struct ovpn_socket *ovpn_socket_new(struct socket *sock, struct ovpn_peer *peer)
                rcu_read_lock();
                ovpn_sock = rcu_dereference_sk_user_data(sk);
                if (ovpn_sock) {
+                       /* something else filled the sk_user_data without
+                        * setting the encap_type. Reject the socket.
+                        */
+                       if (!type) {
+                               ovpn_sock = ERR_PTR(-EBUSY);
+                               rcu_read_unlock();
+                               goto sock_release;
+                       }
+
                        /* socket owned by another ovpn instance, we can't use it */
                        if (ovpn_sock->ovpn != peer->ovpn) {
                                ovpn_sock = ERR_PTR(-EBUSY);