[PATCH ovpn net v2 4/9] ovpn: ensure socket is owned by ovpn before deref sk_user_data

From: Antonio Quartulli <[email protected]>

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 <[email protected]>
---
 drivers/net/ovpn/socket.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/net/ovpn/socket.c b/drivers/net/ovpn/socket.c
index 517caa64a4fe..6cbeb2caaeec 100644
--- 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);
-- 
2.53.0