[D/E][SRU] Fix for CVE-2019-19252

[Connor Kuehl]

https://people.canonical.com/~ubuntu-security/cve/2019/CVE-2019-19252.html

>From the link above:

    "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."

Clean cherry pick into Disco & Eoan.

It looks like Focal already has it.