[PATCH net] vsock: Do not allow binding to VMADDR_PORT_ANY

[Budimir Markovic <markovicbudimir@gmail.com>]

It is possible for a vsock to autobind to VMADDR_PORT_ANY. This can
cause a use-after-free when a connection is made to the bound socket.
The socket returned by accept() also has port VMADDR_PORT_ANY but is not
on the list of unbound sockets. Binding it will result in an extra
refcount decrement similar to the one fixed in fcdd2242c023 (vsock: Keep
the binding until socket destruction).

Modify the check in __vsock_bind_connectible() to also prevent binding
to VMADDR_PORT_ANY.

Fixes: d021c344051a ("VSOCK: Introduce VM Sockets")
Reported-by: Budimir Markovic <markovicbudimir@gmail.com>
Signed-off-by: Budimir Markovic <markovicbudimir@gmail.com>
---
 net/vmw_vsock/af_vsock.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
index ead6a3c14..bebb355f3 100644
--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c
@@ -689,7 +689,8 @@ static int __vsock_bind_connectible(struct vsock_sock *vsk,
 		unsigned int i;
 
 		for (i = 0; i < MAX_PORT_RETRIES; i++) {
-			if (port <= LAST_RESERVED_PORT)
+			if (port == VMADDR_PORT_ANY ||
+			    port <= LAST_RESERVED_PORT)
 				port = LAST_RESERVED_PORT + 1;
 
 			new_addr.svm_port = port++;
-- 
2.49.1