iotests: Specify explicit backing format where sensible

There are many existing qcow2 images that specify a backing file but
no format.  This has been the source of CVEs in the past, but has
become more prominent of a problem now that libvirt has switched to
-blockdev.  With older -drive, at least the probing was always done by
qemu (so the only risk of a changed format between successive boots of
a guest was if qemu was upgraded and probed differently).  But with
newer -blockdev, libvirt must specify a format; if libvirt guesses raw
where the image was formatted, this results in data corruption visible
to the guest; conversely, if libvirt guesses qcow2 where qemu was
using raw, this can result in potential security holes, so modern
libvirt instead refuses to use images without explicit backing format.

The change in libvirt to reject images without explicit backing format
has pointed out that a number of tools have been far too reliant on
probing in the past.  It's time to set a better example in our own
iotests of properly setting this parameter.

iotest calls to create, rebase, and convert are all impacted to some
degree.  It's a bit annoying that we are inconsistent on command line
- while all of those accept -o backing_file=...,backing_fmt=..., the
shortcuts are different: create and rebase have -b and -F, while
convert has -B but no -F.  (amend has no shortcuts, but the previous
patch just deprecated the use of amend to change backing chains).

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20200706203954.341758-9-eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 5 insertions, 4 deletions

diff --git a/tests/qemu-iotests/156 b/tests/qemu-iotests/156
index 5559df6..7c69a6c 100755
--- a/tests/qemu-iotests/156
+++ b/tests/qemu-iotests/156
@@ -56,7 +56,7 @@ _unsupported_imgopts data_file
 
 # Create source disk
 TEST_IMG="$TEST_IMG.backing" _make_test_img 1M
-_make_test_img -b "$TEST_IMG.backing" 1M
+_make_test_img -b "$TEST_IMG.backing" -F $IMGFMT 1M
 
 $QEMU_IO -c 'write -P 1 0 256k' "$TEST_IMG.backing" | _filter_qemu_io
 $QEMU_IO -c 'write -P 2 64k 192k' "$TEST_IMG" | _filter_qemu_io
@@ -68,7 +68,7 @@ _send_qemu_cmd $QEMU_HANDLE \
     'return'
 
 # Create snapshot
-TEST_IMG="$TEST_IMG.overlay" _make_test_img -u -b "$TEST_IMG" 1M
+TEST_IMG="$TEST_IMG.overlay" _make_test_img -u -b "$TEST_IMG" -F $IMGFMT 1M
 _send_qemu_cmd $QEMU_HANDLE \
     "{ 'execute': 'blockdev-snapshot-sync',
        'arguments': { 'device': 'source',
@@ -85,7 +85,8 @@ _send_qemu_cmd $QEMU_HANDLE \
     'return'
 
 # Create target image
-TEST_IMG="$TEST_IMG.target.overlay" _make_test_img -u -b "$TEST_IMG.target" 1M
+TEST_IMG="$TEST_IMG.target.overlay" _make_test_img -u -b "$TEST_IMG.target" \
+    -F $IMGFMT 1M
 
 # Mirror snapshot
 _send_qemu_cmd $QEMU_HANDLE \
@@ -111,7 +112,7 @@ _send_qemu_cmd $QEMU_HANDLE \
 # Copy source backing chain to the target before completing the job
 cp "$TEST_IMG.backing" "$TEST_IMG.target.backing"
 cp "$TEST_IMG" "$TEST_IMG.target"
-$QEMU_IMG rebase -u -b "$TEST_IMG.target.backing" "$TEST_IMG.target"
+$QEMU_IMG rebase -u -b "$TEST_IMG.target.backing" -F $IMGFMT "$TEST_IMG.target"
 
 # Complete block job
 _send_qemu_cmd $QEMU_HANDLE \