Re: [PATCH] iotests: Test mirror-top filter permissions

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

31.03.2021 15:28, Max Reitz wrote:
> Add a test accompanying commit 53431b9086b2832ca1aeff0c55e186e9ed79bd11
> ("block/mirror: Fix mirror_top's permissions").
> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
>   tests/qemu-iotests/tests/mirror-top-perms     | 121 ++++++++++++++++++
>   tests/qemu-iotests/tests/mirror-top-perms.out |   5 +
>   2 files changed, 126 insertions(+)
>   create mode 100755 tests/qemu-iotests/tests/mirror-top-perms
>   create mode 100644 tests/qemu-iotests/tests/mirror-top-perms.out
> 
> diff --git a/tests/qemu-iotests/tests/mirror-top-perms b/tests/qemu-iotests/tests/mirror-top-perms
> new file mode 100755
> index 0000000000..451a0666f8
> --- /dev/null
> +++ b/tests/qemu-iotests/tests/mirror-top-perms
> @@ -0,0 +1,121 @@
> +#!/usr/bin/env python3
> +# group: rw
> +#
> +# Test permissions taken by the mirror-top filter
> +#
> +# Copyright (C) 2021 Red Hat, Inc.
> +#
> +# This program is free software; you can redistribute it and/or modify
> +# it under the terms of the GNU General Public License as published by
> +# the Free Software Foundation; either version 2 of the License, or
> +# (at your option) any later version.
> +#
> +# This program is distributed in the hope that it will be useful,
> +# but WITHOUT ANY WARRANTY; without even the implied warranty of
> +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> +# GNU General Public License for more details.
> +#
> +# You should have received a copy of the GNU General Public License
> +# along with this program.  If not, see <http://www.gnu.org/licenses/>.
> +#
> +
> +import os
> +import iotests
> +from iotests import qemu_img
> +
> +# Import qemu after iotests.py has amended sys.path
> +# pylint: disable=wrong-import-order
> +import qemu
> +
> +
> +image_size = 1 * 1024 * 1024
> +source = os.path.join(iotests.test_dir, 'source.img')
> +
> +
> +class TestMirrorTopPerms(iotests.QMPTestCase):
> +    def setUp(self):
> +        assert qemu_img('create', '-f', iotests.imgfmt, source,
> +                        str(image_size)) == 0
> +        self.vm = iotests.VM()
> +        self.vm.add_drive(source)
> +        self.vm.add_blockdev(f'null-co,node-name=null,size={image_size}')
> +        self.vm.launch()
> +
> +        # Will be created by the test function itself
> +        self.vm_b = None
> +
> +    def tearDown(self):
> +        try:
> +            self.vm.shutdown()
> +        except qemu.machine.AbnormalShutdown:
> +            pass
> +
> +        if self.vm_b is not None:
> +            self.vm_b.shutdown()
> +
> +        os.remove(source)
> +
> +    def test_cancel(self):
> +        """
> +        Before commit 53431b9086b28, mirror-top used to not take any
> +        permissions but WRITE and share all permissions.  Because it
> +        is inserted between the source's original parents and the
> +        source, there generally was no parent that would have taken or
> +        unshared any permissions on the source, which means that an
> +        external process could access the image unhindered by locks.
> +        (Unless there was a parent above the protocol node that would
> +        take its own locks, e.g. a format driver.)
> +        This is bad enough, but if the mirror job is then cancelled,
> +        the mirroring VM tries to take back the image, restores the
> +        original permissions taken and unshared, and assumes this must
> +        just work.  But it will not, and so the VM aborts.
> +
> +        Commit 53431b9086b28 made mirror keep the original permissions
> +        and so no other process can "steal" the image.
> +
> +        (Note that you cannot really do the same with the target image
> +        and then completing the job, because the mirror job always
> +        took/unshared the correct permissions on the target.  For
> +        example, it does not share READ_CONSISTENT, which makes it
> +        difficult to let some other qemu process open the image.)
> +        """
> +
> +        result = self.vm.qmp('blockdev-mirror',
> +                             job_id='mirror',
> +                             device='drive0',
> +                             target='null',
> +                             sync='full')
> +        self.assert_qmp(result, 'return', {})
> +
> +        self.vm.event_wait('BLOCK_JOB_READY')
> +
> +        # We want this to fail because the image cannot be locked.
> +        # If it does not fail, continue still and see what happens.

This comment is about vm_b.launch(), not about creating vm object. Probably better to move it down

> +        self.vm_b = iotests.VM(path_suffix='b')
> +        # Must use -blockdev -device so we can use share-rw.
> +        # (And we need share-rw=on because mirror-top was always
> +        # forced to take the WRITE permission so it can write to the
> +        # source image.)
> +        self.vm_b.add_blockdev(f'file,node-name=drive0,filename={source}')
> +        self.vm_b.add_device('virtio-blk,drive=drive0,share-rw=on')
> +        try:
> +            self.vm_b.launch()
> +            print('ERROR: VM B launched successfully, this should not have '
> +                  'happened')

probably iotests.log() is better here.

> +        except qemu.qmp.QMPConnectError:
> +            assert 'Is another process using the image' in self.vm_b.get_log()
> +
> +        result = self.vm.qmp('block-job-cancel',
> +                             device='mirror')
> +        self.assert_qmp(result, 'return', {})
> +
> +        self.vm.event_wait('BLOCK_JOB_COMPLETED')
> +
> +
> +if __name__ == '__main__':
> +    # No metadata format driver supported, because they would for
> +    # example always unshare the WRITE permission.  The raw driver
> +    # just passes through the permissions from the guest device, and
> +    # those are the permissions that we want to test.
> +    iotests.main(supported_fmts=['raw'],
> +                 supported_protocols=['file'])
> diff --git a/tests/qemu-iotests/tests/mirror-top-perms.out b/tests/qemu-iotests/tests/mirror-top-perms.out
> new file mode 100644
> index 0000000000..ae1213e6f8
> --- /dev/null
> +++ b/tests/qemu-iotests/tests/mirror-top-perms.out
> @@ -0,0 +1,5 @@
> +.
> +----------------------------------------------------------------------
> +Ran 1 tests
> +
> +OK
> 

Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

-- 
Best regards,
Vladimir