[PATCH] vsock: preserve child namespace mode on an empty write

__vsock_net_mode_string() returns success without updating new_mode when
the write length is zero. Its caller then reads the uninitialized enum and
may permanently store a stack-derived value in the write-once child mode.

Initialize new_mode from the current child mode so that an empty write is
a no-op.

Fixes: eafb64f40ca4 ("vsock: add netns to vsock core")
Cc: stable@vger.kernel.org
Signed-off-by: Aldo Ariel Panzardo <redacted>
---
 net/vmw_vsock/af_vsock.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
index 622dbd0467..61163357ae 100644
--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c

@@ -2878,6 +2878,7 @@ static int vsock_net_child_mode_string(const struct ctl_table *table, int write,
 	int ret;
 
 	net = container_of(table->data, struct net, vsock.child_ns_mode);
+	new_mode = vsock_net_child_mode(net);
 
 	ret = __vsock_net_mode_string(table, write, buffer, lenp, ppos,
 				      vsock_net_child_mode(net), &new_mode);

-- 
2.43.0