[PATCH 4.9 33/49] vsock/virtio: update credit only if socket is not closed

[Greg Kroah-Hartman]

From: Stefano Garzarella <sgarzare@xxxxxxxxxx>

commit ce7536bc7398e2ae552d2fabb7e0e371a9f1fe46 upstream.

If the socket is closed or is being released, some resources used by
virtio_transport_space_update() such as 'vsk->trans' may be released.

To avoid a use after free bug we should only update the available credit
when we are sure the socket is still open and we have the lock held.

Fixes: 06a8fc78367d ("VSOCK: Introduce virtio_vsock_common.ko")
Signed-off-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>
Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20210208144454.84438-1-sgarzare@xxxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 net/vmw_vsock/virtio_transport_common.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -959,10 +959,10 @@ void virtio_transport_recv_pkt(struct vi
 
 	vsk = vsock_sk(sk);
 
-	space_available = virtio_transport_space_update(sk, pkt);
-
 	lock_sock(sk);
 
+	space_available = virtio_transport_space_update(sk, pkt);
+
 	/* Update CID in case it has changed after a transport reset event */
 	vsk->local_addr.svm_cid = dst.svm_cid;