vmm: fix vsock with landlock

Without write access to the directory the socket will go in, it's not
possible to create the socket.

I've tested outgoing connections from the VM, and they don't seem to
need read permissions on that directory to connect to a socket on the
host.

Fixes: b3e5738b4 ("vmm: Introduce ApplyLandlock trait")
Signed-off-by: Alyssa Ross <hi@alyssa.is>

vmm/src/vm_config.rs

@@ -647,7 +647,12 @@ pub struct VsockConfig {
 
 impl ApplyLandlock for VsockConfig {
     fn apply_landlock(&self, landlock: &mut Landlock) -> LandlockResult<()> {
+        if let Some(parent) = self.socket.parent() {
+            landlock.add_rule_with_access(parent, "w")?;
+        }
+
         landlock.add_rule_with_access(&self.socket, "rw")?;
+
         Ok(())
     }
 }