b66ff2c298
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>
117 lines
4.3 KiB
Python
Executable File
117 lines
4.3 KiB
Python
Executable File
#!/usr/bin/env python3
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#
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# Copy-on-read tests using a COR filter node
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#
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# Copyright (C) 2018 Red Hat, Inc.
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#
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 2 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program. If not, see <http://www.gnu.org/licenses/>.
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#
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# Creator/Owner: Max Reitz <mreitz@redhat.com>
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import iotests
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from iotests import log, qemu_img, qemu_io_silent
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# Need backing file support
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iotests.script_initialize(supported_fmts=['qcow2', 'qcow', 'qed', 'vmdk'],
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supported_platforms=['linux'])
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log('')
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log('=== Copy-on-read across nodes ===')
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log('')
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# The old copy-on-read mechanism without a filter node cannot request
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# WRITE_UNCHANGED permissions for its child. Therefore it just tries
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# to sneak its write by the usual permission system and holds its
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# fingers crossed. However, that sneaking does not work so well when
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# there is a filter node in the way: That will receive the write
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# request and re-issue a new one to its child, which this time is a
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# proper write request that will make the permission system cough --
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# unless there is someone at the top (like a guest device) that has
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# requested write permissions.
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#
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# A COR filter node, however, can request the proper permissions for
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# its child and therefore is not hit by this issue.
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with iotests.FilePath('base.img') as base_img_path, \
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iotests.FilePath('top.img') as top_img_path, \
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iotests.VM() as vm:
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log('--- Setting up images ---')
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log('')
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assert qemu_img('create', '-f', iotests.imgfmt, base_img_path, '64M') == 0
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assert qemu_io_silent(base_img_path, '-c', 'write -P 1 0M 1M') == 0
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assert qemu_img('create', '-f', iotests.imgfmt, '-b', base_img_path,
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'-F', iotests.imgfmt, top_img_path) == 0
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assert qemu_io_silent(top_img_path, '-c', 'write -P 2 1M 1M') == 0
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log('Done')
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log('')
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log('--- Doing COR ---')
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log('')
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# Compare with e.g. the following:
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# vm.add_drive_raw('if=none,node-name=node0,copy-on-read=on,driver=raw,' \
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# 'file.driver=%s,file.file.filename=%s' %
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# (iotests.imgfmt, top_img_path))
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# (Remove the blockdev-add instead.)
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# ((Not tested here because it hits an assertion in the permission
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# system.))
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vm.launch()
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log(vm.qmp('blockdev-add',
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node_name='node0',
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driver='copy-on-read',
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file={
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'driver': 'raw',
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'file': {
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'driver': 'copy-on-read',
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'file': {
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'driver': 'raw',
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'file': {
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'driver': iotests.imgfmt,
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'file': {
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'driver': 'file',
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'filename': top_img_path
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},
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'backing': {
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'driver': iotests.imgfmt,
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'file': {
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'driver': 'file',
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'filename': base_img_path
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}
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}
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}
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}
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}
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}))
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# Trigger COR
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log(vm.qmp('human-monitor-command',
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command_line='qemu-io node0 "read 0 64M"'))
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vm.shutdown()
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log('')
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log('--- Checking COR result ---')
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log('')
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assert qemu_io_silent(base_img_path, '-c', 'discard 0 64M') == 0
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assert qemu_io_silent(top_img_path, '-c', 'read -P 1 0M 1M') == 0
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assert qemu_io_silent(top_img_path, '-c', 'read -P 2 1M 1M') == 0
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log('Done')
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