[PATCH 5.10.y] vsock: prevent null-ptr-deref in vsock_*[has_data|has_space]

[Stefano Garzarella <sgarzare@redhat.com>]

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/
Link: https://lore.kernel.org/netdev/5ca20d4c-1017-49c2-9516-f6f75fd331e9@rbox.co/
Link: https://lore.kernel.org/netdev/677f84a8.050a0220.25a300.01b3.GAE@google.com/
Co-developed-by: Hyunwoo Kim <v4bel@theori.io>
Signed-off-by: Hyunwoo Kim <v4bel@theori.io>
Co-developed-by: Wongi Lee <qwerty@theori.io>
Signed-off-by: Wongi Lee <qwerty@theori.io>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Reviewed-by: Luigi Leonardi <leonardi@redhat.com>
Reviewed-by: Hyunwoo Kim <v4bel@theori.io>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
(cherry picked from commit 91751e248256efc111e52e15115840c35d85abaf)
[SG: fixed conflict since this tree is missing vsock_connectible_has_data()
 added by commit 0798e78b102b ("af_vsock: rest of SEQPACKET support")]
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
---
 net/vmw_vsock/af_vsock.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
index ce14374bbaca..d1ab66b90f8d 100644
--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c
@@ -828,12 +828,18 @@ 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);
 
 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);
-- 
2.48.1