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

From: Max Reitz <mreitz@redhat.com>
To: qemu-block@nongnu.org
Cc: Kevin Wolf <kwolf@redhat.com>, Alberto Garcia <berto@igalia.com>,
	qemu-devel@nongnu.org, Max Reitz <mreitz@redhat.com>
Subject: [PATCH for-4.2 0/2] qcow2: Fix QCOW2_COMPRESSED_SECTOR_MASK
Date: Mon, 28 Oct 2019 17:18:39 +0100	[thread overview]
Message-ID: <20191028161841.1198-1-mreitz@redhat.com> (raw)

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