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>

diff --git a/hw/usb/hcd-ehci.c b/hw/usb/hcd-ehci.c
index 3ec2824b45a7b4d8b1ff6926cf41bf490fa992fe..8efa43bbdd5e8a22bc89a30794de144fd65e6d35 100644 (file)
--- a/hw/usb/hcd-ehci.c
+++ b/hw/usb/hcd-ehci.c
@@ -1341,7 +1341,7 @@ 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;
 
     dir =(itd->bufptr[1] & ITD_BUFPTR_DIRECTION);
@@ -1431,9 +1431,10 @@ 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;
 }