tests/qemu-iotests/tests/mirror-top-perms

   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
  22 import os
  23 import iotests
  24 from iotests import qemu_img
  25
  26 # Import qemu after iotests.py has amended sys.path
  27 # pylint: disable=wrong-import-order
  28 import qemu
  29
  30
  31 image_size = 1 * 1024 * 1024
  32 source = os.path.join(iotests.test_dir, 'source.img')
  33
  34
  35 class TestMirrorTopPerms(iotests.QMPTestCase):
  36     def setUp(self):
  37         assert qemu_img('create', '-f', iotests.imgfmt, source,
  38                         str(image_size)) == 0
  39         self.vm = iotests.VM()
  40         self.vm.add_drive(source)
  41         self.vm.add_blockdev(f'null-co,node-name=null,size={image_size}')
  42         self.vm.launch()
  43
  44         # Will be created by the test function itself
  45         self.vm_b = None
  46
  47     def tearDown(self):
  48         try:
  49             self.vm.shutdown()
  50         except qemu.machine.machine.AbnormalShutdown:
  51             pass
  52
  53         if self.vm_b is not None:
  54             self.vm_b.shutdown()
  55
  56         os.remove(source)
  57
  58     def test_cancel(self):
  59         """
  60         Before commit 53431b9086b28, mirror-top used to not take any
  61         permissions but WRITE and share all permissions.  Because it
  62         is inserted between the source's original parents and the
  63         source, there generally was no parent that would have taken or
  64         unshared any permissions on the source, which means that an
  65         external process could access the image unhindered by locks.
  66         (Unless there was a parent above the protocol node that would
  67         take its own locks, e.g. a format driver.)
  68         This is bad enough, but if the mirror job is then cancelled,
  69         the mirroring VM tries to take back the image, restores the
  70         original permissions taken and unshared, and assumes this must
  71         just work.  But it will not, and so the VM aborts.
  72
  73         Commit 53431b9086b28 made mirror keep the original permissions
  74         and so no other process can "steal" the image.
  75
  76         (Note that you cannot really do the same with the target image
  77         and then completing the job, because the mirror job always
  78         took/unshared the correct permissions on the target.  For
  79         example, it does not share READ_CONSISTENT, which makes it
  80         difficult to let some other qemu process open the image.)
  81         """
  82
  83         result = self.vm.qmp('blockdev-mirror',
  84                              job_id='mirror',
  85                              device='drive0',
  86                              target='null',
  87                              sync='full')
  88         self.assert_qmp(result, 'return', {})
  89
  90         self.vm.event_wait('BLOCK_JOB_READY')
  91
  92         # We want this to fail because the image cannot be locked.
  93         # If it does not fail, continue still and see what happens.
  94         self.vm_b = iotests.VM(path_suffix='b')
  95         # Must use -blockdev -device so we can use share-rw.
  96         # (And we need share-rw=on because mirror-top was always
  97         # forced to take the WRITE permission so it can write to the
  98         # source image.)
  99         self.vm_b.add_blockdev(f'file,node-name=drive0,filename={source}')
 100         self.vm_b.add_device('virtio-blk,drive=drive0,share-rw=on')
 101         try:
 102             self.vm_b.launch()
 103             print('ERROR: VM B launched successfully, this should not have '
 104                   'happened')
 105         except qemu.qmp.QMPConnectError:
 106             assert 'Is another process using the image' in self.vm_b.get_log()
 107
 108         result = self.vm.qmp('block-job-cancel',
 109                              device='mirror')
 110         self.assert_qmp(result, 'return', {})
 111
 112         self.vm.event_wait('BLOCK_JOB_COMPLETED')
 113
 114
 115 if __name__ == '__main__':
 116     # No metadata format driver supported, because they would for
 117     # example always unshare the WRITE permission.  The raw driver
 118     # just passes through the permissions from the guest device, and
 119     # those are the permissions that we want to test.
 120     iotests.main(supported_fmts=['raw'],
 121                  supported_protocols=['file'])