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From: Gerd Hoffmann <kraxel@redhat.com>
Date: Mon, 14 Dec 2015 09:21:23 +0100
Subject: [PATCH] ehci: make idt processing more robust

Make ehci_process_itd return an error in case we didn't do any actual
iso transfer because we've found no active transaction.  That'll avoid
ehci happily run in circles forever if the guest builds a loop out of
idts.

This is CVE-2015-8558.

Cc: qemu-stable@nongnu.org
Reported-by: Qinghao Tang <luodalongde@gmail.com>
Tested-by: P J P <ppandit@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
(cherry picked from commit 156a2e4dbffa85997636a7a39ef12da6f1b40254)
---
 hw/usb/hcd-ehci.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/hw/usb/hcd-ehci.c b/hw/usb/hcd-ehci.c
index d4d7547..51d39c6 100644
--- a/hw/usb/hcd-ehci.c
+++ b/hw/usb/hcd-ehci.c
@@ -1389,7 +1389,7 @@ static int ehci_process_itd(EHCIState *ehci,
 {
     USBDevice *dev;
     USBEndpoint *ep;
-    uint32_t i, len, pid, dir, devaddr, endp;
+    uint32_t i, len, pid, dir, devaddr, endp, xfers = 0;
     uint32_t pg, off, ptr1, ptr2, max, mult;
 
     ehci->periodic_sched_active = PERIODIC_ACTIVE;
@@ -1479,9 +1479,10 @@ static int ehci_process_itd(EHCIState *ehci,
                 ehci_raise_irq(ehci, USBSTS_INT);
             }
             itd->transact[i] &= ~ITD_XACT_ACTIVE;
+            xfers++;
         }
     }
-    return 0;
+    return xfers ? 0 : -1;
 }