1#!/usr/bin/env python3
2# group: rw
3#
4# Test permissions taken by the mirror-top filter
5#
6# Copyright (C) 2021 Red Hat, Inc.
7#
8# This program is free software; you can redistribute it and/or modify
9# it under the terms of the GNU General Public License as published by
10# the Free Software Foundation; either version 2 of the License, or
11# (at your option) any later version.
12#
13# This program is distributed in the hope that it will be useful,
14# but WITHOUT ANY WARRANTY; without even the implied warranty of
15# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
16# GNU General Public License for more details.
17#
18# You should have received a copy of the GNU General Public License
19# along with this program.  If not, see <http://www.gnu.org/licenses/>.
20#
21
22import os
23
24from qemu.machine import machine
25
26import iotests
27from iotests import change_log_level, qemu_img
28
29
30image_size = 1 * 1024 * 1024
31source = os.path.join(iotests.test_dir, 'source.img')
32
33
34class TestMirrorTopPerms(iotests.QMPTestCase):
35    def setUp(self):
36        qemu_img('create', '-f', iotests.imgfmt, source, str(image_size))
37        self.vm = iotests.VM()
38        self.vm.add_drive(source)
39        self.vm.add_blockdev(f'null-co,node-name=null,size={image_size}')
40        self.vm.launch()
41
42        # Will be created by the test function itself
43        self.vm_b = None
44
45    def tearDown(self):
46        try:
47            self.vm.shutdown()
48        except machine.AbnormalShutdown:
49            pass
50
51        if self.vm_b is not None:
52            self.vm_b.shutdown()
53
54        os.remove(source)
55
56    def test_cancel(self):
57        """
58        Before commit 53431b9086b28, mirror-top used to not take any
59        permissions but WRITE and share all permissions.  Because it
60        is inserted between the source's original parents and the
61        source, there generally was no parent that would have taken or
62        unshared any permissions on the source, which means that an
63        external process could access the image unhindered by locks.
64        (Unless there was a parent above the protocol node that would
65        take its own locks, e.g. a format driver.)
66        This is bad enough, but if the mirror job is then cancelled,
67        the mirroring VM tries to take back the image, restores the
68        original permissions taken and unshared, and assumes this must
69        just work.  But it will not, and so the VM aborts.
70
71        Commit 53431b9086b28 made mirror keep the original permissions
72        and so no other process can "steal" the image.
73
74        (Note that you cannot really do the same with the target image
75        and then completing the job, because the mirror job always
76        took/unshared the correct permissions on the target.  For
77        example, it does not share READ_CONSISTENT, which makes it
78        difficult to let some other qemu process open the image.)
79        """
80
81        self.vm.cmd('blockdev-mirror',
82                    job_id='mirror',
83                    device='drive0',
84                    target='null',
85                    sync='full')
86
87        self.vm.event_wait('BLOCK_JOB_READY')
88
89        # We want this to fail because the image cannot be locked.
90        # If it does not fail, continue still and see what happens.
91        self.vm_b = iotests.VM(path_suffix='b')
92        # Must use -blockdev -device so we can use share-rw.
93        # (And we need share-rw=on because mirror-top was always
94        # forced to take the WRITE permission so it can write to the
95        # source image.)
96        self.vm_b.add_blockdev(f'file,node-name=drive0,filename={source}')
97        self.vm_b.add_device('virtio-blk,drive=drive0,share-rw=on')
98        try:
99            # Silence QMP logging errors temporarily.
100            with change_log_level('qemu.qmp'):
101                self.vm_b.launch()
102                print('ERROR: VM B launched successfully, '
103                      'this should not have happened')
104        except machine.VMLaunchFailure as exc:
105            assert 'Is another process using the image' in exc.output
106
107        self.vm.cmd('block-job-cancel',
108                    device='mirror')
109
110        self.vm.event_wait('BLOCK_JOB_COMPLETED')
111
112
113if __name__ == '__main__':
114    # No metadata format driver supported, because they would for
115    # example always unshare the WRITE permission.  The raw driver
116    # just passes through the permissions from the guest device, and
117    # those are the permissions that we want to test.
118    iotests.main(supported_fmts=['raw'],
119                 supported_protocols=['file'])
120