xen/blkfront: fix leaking data in shared pages

xen/blkfront: fix leaking data in shared pages

Origin: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit?id=cfea428030be836d79a7690968232bb7fa4410f1
Bug-Debian-Security: https://security-tracker.debian.org/tracker/CVE-2022-26365

commit 2f446ffe9d737e9a844b97887919c4fda18246e7 upstream.

When allocating pages to be used for shared communication with the
backend always zero them, this avoids leaking unintended data present
on the pages.

This is CVE-2022-26365, part of XSA-403.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Gbp-Pq: Topic bugfix/all
Gbp-Pq: Name xen-blkfront-fix-leaking-data-in-shared-pages.patch