[Bug 1523811] Re: USB assert failure on dev-storage.c

[Philippe Mathieu-Daudé]

Looking at commit 0659879e6e5 ("usb-storage: remove MSDState->residue")
this assert seems a left-over, CSW residue should be irrelevant in CBW
path...
Gerd, can we simply remove it?

** Changed in: qemu
       Status: Expired => Confirmed

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https://bugs.launchpad.net/bugs/1523811

Title:
  USB assert failure on dev-storage.c

Status in QEMU:
  Confirmed

Bug description:
  On executing the attached python script in the guest OS, QEMU dies
  with assert failure:

  [run python script in guest root shell]
  # python a.py

  [host message]
  qemu-system-x86_64: hw/usb/dev-storage.c:445: usb_msd_handle_data: Assertion 
`le32_to_cpu(s->csw.residue) == 0' failed.
  Aborted (core dumped)

  When I detach the kernel driver and send CBW and reattach it again, without 
conforming to the command/data/status protocol, QEMU dies.
  I think this is due to misimplementation of Command/Data/Status protocol in 
Bulk-only transfer.
  This kind of assert failure can be misused by malwares to avoid being 
analyzed by terminating only in the virtual environments and still execute the 
malicious code in real machines.
  Before running python script, make sure to change a.py that it should points 
to usb mass storage's vid and pid.

  QEMU was running on these environment :
  [CPU model]    Intel(R) Core(TM) i5-4590 CPU @ 3.30GHz
  [qemu version] QEMU 2.5.0-rc2 (compiled from source, gcc 4.8.4)
  [host info]    Ubuntu 14.04.3, x86_64, 3.19.0-32-generic
  [guest info]   Ubuntu 14.04.3, x86_64, 3.19.0-28-generic
  [QEMU argument]
  x86_64-softmmu/qemu-system-x86_64 -hda /media/hdd/img/ubuntu1404.qcow2.5 \
   -m 512 \
   --usbdevice disk:format=qcow2:../usb.img.5 \
   --enable-kvm

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