Recent reports have shown how we sometimes call vsock_*_has_data()
when a vsock socket has been de-assigned from a transport (see attached
links), but we shouldn't.

Previous commits should have solved the real problems, but we may have
more in the future, so to avoid null-ptr-deref, we can return 0
(no space, no data available) but with a warning.

This way the code should continue to run in a nearly consistent state
and have a warning that allows us to debug future problems.

Fixes: c0cfa2d8a788 ("vsock: add multi-transports support")
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/netdev/Z2K%2FI4nlHdfMRTZC@v4bel-B760M-AORUS-ELITE-AX/ (local)
Link: https://lore.kernel.org/netdev/5ca20d4c-1017-49c2-9516-f6f75fd331e9@rbox.co/ (local)
Link: https://lore.kernel.org/netdev/677f84a8.050a0220.25a300.01b3.GAE@google.com/ (local)
Co-developed-by: Hyunwoo Kim <redacted>
Signed-off-by: Hyunwoo Kim <redacted>
Co-developed-by: Wongi Lee <redacted>
Signed-off-by: Wongi Lee <redacted>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
---
net/vmw_vsock/af_vsock.c | 9 +++++++++
1 file changed, 9 insertions(+)

diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
index 74d35a871644..fa9d1b49599b 100644
--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c

@@ -879,6 +879,9 @@ EXPORT_SYMBOL_GPL(vsock_create_connected);

s64 vsock_stream_has_data(struct vsock_sock *vsk)
{
+	if (WARN_ON(!vsk->transport))
+		return 0;
+
	return vsk->transport->stream_has_data(vsk);
}
EXPORT_SYMBOL_GPL(vsock_stream_has_data);

@@ -887,6 +890,9 @@ s64 vsock_connectible_has_data(struct vsock_sock *vsk)

{
	struct sock *sk = sk_vsock(vsk);

+	if (WARN_ON(!vsk->transport))
+		return 0;
+
	if (sk->sk_type == SOCK_SEQPACKET)
		return vsk->transport->seqpacket_has_data(vsk);
	else

@@ -896,6 +902,9 @@ EXPORT_SYMBOL_GPL(vsock_connectible_has_data);

s64 vsock_stream_has_space(struct vsock_sock *vsk)
{
+	if (WARN_ON(!vsk->transport))
+		return 0;
+
	return vsk->transport->stream_has_space(vsk);
}
EXPORT_SYMBOL_GPL(vsock_stream_has_space);
-- 
2.47.1