vcs_write in drivers/tty/vt/vc_screen.c in the Linux kernel through 5.3.13 does not prevent write access to vcsu devices, aka CID-0c9acb1af77a.
https://lore.kernel.org/lkml/c30fc539-68a8-65d7-226c-6f8e6fd8bdfb%40suse.com/
https://security.netapp.com/advisory/ntap-20200103-0001/