[PATCH for-4.2 0/2] qcow2: Fix QCOW2_COMPRESSED_SECTOR_MASK

[Max Reitz]

This fixes a bug reported on
https://bugs.launchpad.net/qemu/+bug/1850000.  The problem is that
QCOW2_COMPRESSED_SECTOR_MASK is a 32-bit mask when it really needs to be
a 64-bit mask.

The launchpad report mentions only problems with qemu-img check on large
compressed images, but I think it might extend further than that:
- I suppose qcow2_free_any_clusters() would free every compressed offset
  modulo 4G, which isn’t good
- qcow2_update_snapshot_refcount() will probably update compressed
  cluster’s refcounts (in snapshots) modulo 4G, which also isn’t good
- And then we have check_refcount_l2() which updates the wrong clusters
  for qemu-img check (as demonstrated in the bug report)

- (qcow2_co_preadv_compressed() is safe because it uses the inverted
  mask, which of course is again just 32 bit)


But I haven’t tested those other cases.


Max Reitz (2):
  qcow2: Fix QCOW2_COMPRESSED_SECTOR_MASK
  iotests: Add test for 4G+ compressed qcow2 write

 block/qcow2.h              |  2 +-
 tests/qemu-iotests/272     | 79 ++++++++++++++++++++++++++++++++++++++
 tests/qemu-iotests/272.out | 10 +++++
 tests/qemu-iotests/group   |  1 +
 4 files changed, 91 insertions(+), 1 deletion(-)
 create mode 100755 tests/qemu-iotests/272
 create mode 100644 tests/qemu-iotests/272.out

-- 
2.21.0