usb: limit combined packets to 1 MiB (CVE-2021-3527)

usb: limit combined packets to 1 MiB (CVE-2021-3527)

usb-host and usb-redirect try to batch bulk transfers by combining many
small usb packets into a single, large transfer request, to reduce the
overhead and improve performance.

This patch adds a size limit of 1 MiB for those combined packets to
restrict the host resources the guest can bind that way.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Message-Id: <20210503132915.2335822-6-kraxel@redhat.com>
(cherry picked from commit 05a40b172e4d691371534828078be47e7fff524c)
Signed-off-by: Michael Roth <michael.roth@amd.com>