Red Hat: CVE-2026-31786: kernel: Buffer overflow in drivers/xen/sys-hypervisor.c (Multiple Advisories)

In the Linux kernel, the following vulnerability has been resolved:

Buffer overflow in drivers/xen/sys-hypervisor.c

The build id returned by HYPERVISOR_xen_version(XENVER_build_id) is
neither NUL terminated nor a string.

The first causes a buffer overflow as sprintf in buildid_show will
read and copy till it finds a NUL.

00000000 f4 91 51 f4 dd 38 9e 9d 65 47 52 eb 10 71 db 50 |..Q..8..eGR..q.P|
00000010 b9 a8 01 42 6f 2e 32 |...Bo.2|
00000017

So use a memcpy instead of sprintf to have the correct value:

00000000 f4 91 51 f4 dd 00 9e 9d 65 47 52 eb 10 71 db 50 |..Q.....eGR..q.P|
00000010 b9 a8 01 42 |...B|
00000014

(the above have a hack to embed a zero inside and check it's
returned correctly).

This is XSA-485 / CVE-2026-31786