[SRU Groovy,Focal/linux-oem-5.6] CVE-2020-28974

[Thadeu Lima de Souza Cascardo]

[Impact]
Slab OOB read because of VT font manipulation.

[Test case]
The ioctl is gone now, returning EINVAL.

copyfont.c:
#include <linux/kd.h>
#include <sys/ioctl.h>
int main(){struct console_font_op op = {.op = KD_FONT_OP_COPY, }; return ioctl(1, KDFONTOP, &op); }

strace -eioctl ./copyfont > /dev/tty8

[Regression potential]
Some versions of systemd supported such ioctl for a time, but it ignored the
ioctl result, it seems.

This has been backported to other series, though.