On Wed, Feb 26, 2020 at 20:39:26 -0600, Eric Blake wrote:
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, convert, and amend 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, convert
has -B but no -F, and amend has no shortcuts.
Signed-off-by: Eric Blake <address@hidden>
---
[...]
113 files changed, 414 insertions(+), 338 deletions(-)
diff --git a/tests/qemu-iotests/017 b/tests/qemu-iotests/017
index 0a4b854e6520..585512bb296b 100755
--- a/tests/qemu-iotests/017
+++ b/tests/qemu-iotests/017
@@ -66,7 +66,7 @@ echo "Creating test image with backing file"
echo
TEST_IMG=$TEST_IMG_SAVE
-_make_test_img -b "$TEST_IMG.base" 6G
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT 6G
My understanding of the intricacies of the qemu-iotest suite is not good
enoug to be able to review this patch. Specifically $IMGFMT in this
instance is also used in the '-f' switch of qemu-img in _make_test_img
and I don't know if it's expected for the backing file to share the
format.