On a Thursday in 2020, Peter Krempa wrote:
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 <eblake@xxxxxxxxxx> ---[...]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 6GMy 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.
IMGFMT is also used for the earlier creation of the base image and I did not see it changing in any of the tests. Jano
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