vsock: Ignore signal/timeout on connect() if already established

During connect(), acting on a signal/timeout by disconnecting an already
established socket leads to several issues:

1. connect() invoking vsock_transport_cancel_pkt() ->
   virtio_transport_purge_skbs() may race with sendmsg() invoking
   virtio_transport_get_credit(). This results in a permanently elevated
   `vvs->bytes_unsent`. Which, in turn, confuses the SOCK_LINGER handling.

2. connect() resetting a connected socket's state may race with socket
   being placed in a sockmap. A disconnected socket remaining in a sockmap
   breaks sockmap's assumptions. And gives rise to WARNs.

3. connect() transitioning SS_CONNECTED -> SS_UNCONNECTED allows for a
   transport change/drop after TCP_ESTABLISHED. Which poses a problem for
   any simultaneous sendmsg() or connect() and may result in a
   use-after-free/null-ptr-deref.

Do not disconnect socket on signal/timeout. Keep the logic for unconnected
sockets: they don't linger, can't be placed in a sockmap, are rejected by
sendmsg().

[1]: https://lore.kernel.org/netdev/e07fd95c-9a38-4eea-9638-133e38c2ec9b@rbox.co/
[2]: https://lore.kernel.org/netdev/20250317-vsock-trans-signal-race-v4-0-fc8837f3f1d4@rbox.co/
[3]: https://lore.kernel.org/netdev/60f1b7db-3099-4f6a-875e-af9f6ef194f6@rbox.co/

Fixes: d021c344051a ("VSOCK: Introduce VM Sockets")
Signed-off-by: Michal Luczaj <mhal@rbox.co>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Link: https://patch.msgid.link/20251119-vsock-interrupted-connect-v2-1-70734cf1233f@rbox.co
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
index 76763247a377a6ad9b12375e19c89d557fbfd038..a9ca9c3b87b31a3f5f3fdfbc9ca7cbc107db29f9 100644 (file)
--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c
@@ -1661,18 +1661,40 @@ static int vsock_connect(struct socket *sock, struct sockaddr *addr,
                timeout = schedule_timeout(timeout);
                lock_sock(sk);
 
-               if (signal_pending(current)) {
-                       err = sock_intr_errno(timeout);
-                       sk->sk_state = sk->sk_state == TCP_ESTABLISHED ? TCP_CLOSING : TCP_CLOSE;
-                       sock->state = SS_UNCONNECTED;
-                       vsock_transport_cancel_pkt(vsk);
-                       vsock_remove_connected(vsk);
-                       goto out_wait;
-               } else if ((sk->sk_state != TCP_ESTABLISHED) && (timeout == 0)) {
-                       err = -ETIMEDOUT;
+               /* Connection established. Whatever happens to socket once we
+                * release it, that's not connect()'s concern. No need to go
+                * into signal and timeout handling. Call it a day.
+                *
+                * Note that allowing to "reset" an already established socket
+                * here is racy and insecure.
+                */
+               if (sk->sk_state == TCP_ESTABLISHED)
+                       break;
+
+               /* If connection was _not_ established and a signal/timeout came
+                * to be, we want the socket's state reset. User space may want
+                * to retry.
+                *
+                * sk_state != TCP_ESTABLISHED implies that socket is not on
+                * vsock_connected_table. We keep the binding and the transport
+                * assigned.
+                */
+               if (signal_pending(current) || timeout == 0) {
+                       err = timeout == 0 ? -ETIMEDOUT : sock_intr_errno(timeout);
+
+                       /* Listener might have already responded with
+                        * VIRTIO_VSOCK_OP_RESPONSE. Its handling expects our
+                        * sk_state == TCP_SYN_SENT, which hereby we break.
+                        * In such case VIRTIO_VSOCK_OP_RST will follow.
+                        */
                        sk->sk_state = TCP_CLOSE;
                        sock->state = SS_UNCONNECTED;
+
+                       /* Try to cancel VIRTIO_VSOCK_OP_REQUEST skb sent out by
+                        * transport->connect().
+                        */
                        vsock_transport_cancel_pkt(vsk);
+
                        goto out_wait;
                }