[PULL 6/6] usb: limit combined packets to 1 MiB (CVE-2021-3527)

[Gerd Hoffmann <kraxel@redhat.com>]

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>
---
 hw/usb/combined-packet.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/hw/usb/combined-packet.c b/hw/usb/combined-packet.c
index 5d57e883dcb5..e56802f89a32 100644
--- a/hw/usb/combined-packet.c
+++ b/hw/usb/combined-packet.c
@@ -171,7 +171,9 @@ void usb_ep_combine_input_packets(USBEndpoint *ep)
         if ((p->iov.size % ep->max_packet_size) != 0 || !p->short_not_ok ||
                 next == NULL ||
                 /* Work around for Linux usbfs bulk splitting + migration */
-                (totalsize == (16 * KiB - 36) && p->int_req)) {
+                (totalsize == (16 * KiB - 36) && p->int_req) ||
+                /* Next package may grow combined package over 1MiB */
+                totalsize > 1 * MiB - ep->max_packet_size) {
             usb_device_handle_data(ep->dev, first);
             assert(first->status == USB_RET_ASYNC);
             if (first->combined) {
-- 
2.31.1