[PATCH net v2 3/5] vsock: Enforce no-transport invariant for TCP_LISTEN sockets

[Michal Luczaj <mhal@rbox.co>]

A non-blocking connect() running in parallel with a blocking connect(),
combined with a racy listen() that hits right after a connect timeout:
TCP_SYN_SENT -> TCP_CLOSE -> TCP_LISTEN, while the connect() loop is still
in progress.

Enforce the invariant. Prevent a socket from becoming a listener after
acquiring a transport.

Fixes: c0cfa2d8a788 ("vsock: add multi-transports support")
Signed-off-by: Michal Luczaj <mhal@rbox.co>
---
 net/vmw_vsock/af_vsock.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
index f840498b58af..499e902becfa 100644
--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c
@@ -1973,13 +1973,13 @@ static int vsock_listen(struct socket *sock, int backlog)
 		goto out;
 	}
 
-	if (sock->state != SS_UNCONNECTED) {
+	vsk = vsock_sk(sk);
+
+	if (sock->state != SS_UNCONNECTED || vsk->transport) {
 		err = -EINVAL;
 		goto out;
 	}
 
-	vsk = vsock_sk(sk);
-
 	if (!vsock_addr_bound(&vsk->local_addr)) {
 		err = -EINVAL;
 		goto out;

-- 
2.55.0