[Bug 1909247] Re: QEMU: use after free vulnerability in esp_do_dma() in hw/scsi/esp.c

[Mark Cave-Ayland]

If Alex is interested in having a fuzz-proof device as a starting point
for fuzzing QEMU's SCSI layer then I don't mind doing the basic work as
I've spent a few months deep in the internals of the ESP controller, and
it makes sense to look at this whilst it is all still fresh. I'd say
there's at least one more set of ESP changes already waiting for after
the 6.0 release.

PJP:
Your change to esp-pci.c looks like a genuine issue, although there is an 
inconsistency within ESP as to what determines whether a request is in progress 
or not. My v2 patchset above uses the request member being non-NULL to indicate 
a valid request, but this should be made consistent throughout the driver.

Can you provide a qtest reproducer so that it can be incorporated into
the test included in the v2 patchset and also allow me to check that
this issue has been fixed?

Alex:
If you can try PJP's patch to esp-pci.c and if you still see some issues then 
please update this bug with a test case or two, and I will look at them when I 
get a moment.

Mauro:
Thanks for the test case - again I shall look at this when I have some 
available time.

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https://bugs.launchpad.net/bugs/1909247

Title:
  QEMU: use after free vulnerability in esp_do_dma() in hw/scsi/esp.c

Status in QEMU:
  New

Bug description:
  A use-after-free vulnerability was found in the am53c974 SCSI host bus
  adapter emulation of QEMU. It could occur in the esp_do_dma() function
  in hw/scsi/esp.c while handling the 'Information Transfer' command
  (CMD_TI). A privileged guest user may abuse this flaw to crash the
  QEMU process on the host, resulting in a denial of service or
  potential code execution with the privileges of the QEMU process.

  This issue was reported by Cheolwoo Myung (Seoul National University).

  Original report:
  Using hypervisor fuzzer, hyfuzz, I found a use-after-free issue in
  am53c974 emulator of QEMU enabled ASan.

  It occurs while transferring information, as it does not check the
  buffer to be transferred.

  A malicious guest user/process could use this flaw to crash the QEMU
  process resulting in DoS scenario.

  To reproduce this issue, please run the QEMU with the following command
  line.

  # To enable ASan option, please set configuration with the following
  $ ./configure --target-list=i386-softmmu --disable-werror --enable-sanitizers
  $ make

  # To reproduce this issue, please run the QEMU process with the following 
command line
  $ ./qemu-system-i386 -m 512 -drive 
file=./hyfuzz.img,index=0,media=disk,format=raw \
  -device am53c974,id=scsi -device scsi-hd,drive=SysDisk \
  -drive id=SysDisk,if=none,file=./disk.img

  Please find attached the disk images to reproduce this issue.

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