[PATCH net] vsock: do not reset a socket in connect() once it has connected

[Hyunwoo Kim <imv4bel@gmail.com>]

commit 002541ef650b ("vsock: Ignore signal/timeout on connect() if
already established") stopped connect() from resetting an established
socket. The check only looks at whether sk_state is TCP_ESTABLISHED at
that moment, and the state can change while connect() sleeps.

A peer RST moves the socket to TCP_CLOSING, and it is not removed from
vsock_connected_table on that path. connect() then wakes up, fails the
check, and resets a socket that had actually connected to TCP_CLOSE and
SS_UNCONNECTED.

The socket can now be connected again while it is still on the table.
Reconnecting to an address served by a different transport makes
vsock_assign_transport() drop the transport from a live socket and free
vsk->trans, even if skbs it already sent are still in flight.
Reconnecting to the same address inserts a node that is already on the
table, provided shutdown() has cleared SOCK_DONE in between.

sock->state cannot be used for the check either. shutdown() overwrites
SS_CONNECTED with SS_DISCONNECTING.

Record on the socket that the connection completed, and check that
instead. The sk_err path after the loop does the same reset, so guard it
as well.

Fixes: d021c344051a ("VSOCK: Introduce VM Sockets")
Cc: stable@vger.kernel.org
Signed-off-by: Hyunwoo Kim <imv4bel@gmail.com>
---
 include/net/af_vsock.h   |  2 ++
 net/vmw_vsock/af_vsock.c | 12 ++++++++----
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
index 30046a3c20f735..d7ec976ed6e272 100644
--- a/include/net/af_vsock.h
+++ b/include/net/af_vsock.h
@@ -63,6 +63,8 @@ struct vsock_sock {
 	struct delayed_work pending_work;
 	struct delayed_work close_work;
 	bool close_work_scheduled;
+	/* Set once the connection completed; never cleared. */
+	bool ever_connected;
 	u32 peer_shutdown;
 	bool sent_request;
 	bool ignore_connecting_rst;
diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
index 622dbd04679944..735c91bb762242 100644
--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c
@@ -351,6 +351,8 @@ void vsock_insert_connected(struct vsock_sock *vsk)
 	struct list_head *list = vsock_connected_sockets(
 		&vsk->remote_addr, &vsk->local_addr);
 
+	vsk->ever_connected = true;
+
 	spin_lock_bh(&vsock_table_lock);
 	__vsock_insert_connected(list, vsk);
 	spin_unlock_bh(&vsock_table_lock);
@@ -1814,14 +1816,14 @@ static int vsock_connect(struct socket *sock, struct sockaddr_unsized *addr,
 		 * Note that allowing to "reset" an already established socket
 		 * here is racy and insecure.
 		 */
-		if (sk->sk_state == TCP_ESTABLISHED)
+		if (vsk->ever_connected)
 			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
+		 * !ever_connected implies that socket is not on
 		 * vsock_connected_table. We keep the binding and the transport
 		 * assigned.
 		 */
@@ -1849,8 +1851,10 @@ static int vsock_connect(struct socket *sock, struct sockaddr_unsized *addr,
 
 	if (sk->sk_err) {
 		err = -sk->sk_err;
-		sk->sk_state = TCP_CLOSE;
-		sock->state = SS_UNCONNECTED;
+		if (!vsk->ever_connected) {
+			sk->sk_state = TCP_CLOSE;
+			sock->state = SS_UNCONNECTED;
+		}
 	} else {
 		err = 0;
 	}
-- 
2.43.0