ovpn: fix peer refcount leak in TCP error paths

In the Linux kernel, the following vulnerability has been resolved: ovpn: fix peer refcount leak in TCP error paths When either the TCP RX or TX error path calls ovpn_peer_hold() followed by schedule_work(&peer->tcp.defer_del_work), and the work item is already pending from the other path, schedule_work() returns false and the work runs only once. Since ovpn_tcp_peer_del_work() calls ovpn_peer_put() exactly once, the extra reference taken by the losing path is never dropped, leaking the peer object. The race window: CPU0 (strparser/RX error): CPU1 (tcp_tx_work/TX error): ovpn_peer_hold() <- refcnt+1 ovpn_peer_hold() <- refcnt+2 schedule_work() <- queued schedule_work() <- NO-OP (work already pending) ovpn_tcp_peer_del_work runs: ovpn_peer_del() ovpn_peer_put() <- refcnt+1 <- peer never freed Fix by checking the return value of schedule_work() in both paths and calling ovpn_peer_put() to drop the extra reference if the work was already pending. ovpn_peer_hold() is kept unconditional in the TX path as it cannot fail at that point.