From 0e6b4a06ad72ac68ec41bab2063f8d167e8e277e Mon Sep 17 00:00:00 2001 From: Matthew Booth Date: Thu, 10 Dec 2015 16:34:19 +0000 Subject: [PATCH 2/3] Fix format conversion in libvirt snapshot The libvirt driver was calling images.convert_image during snapshot to convert snapshots to the intended output format. However, this function does not take the input format as an argument, meaning it implicitly does format detection. This opened an exploit for setups using raw storage on the backend, including raw on filesystem, LVM, and RBD (Ceph). An authenticated user could write a qcow2 header to their instance's disk which specified an arbitrary backing file on the host. When convert_image ran during snapshot, this would then write the contents of the backing file to glance, which is then available to the user. If the setup uses an LVM backend this conversion runs as root, meaning the user can exfiltrate any file on the host, including raw disks. This change adds an input format to convert_image. Partial-Bug: #1524274 Change-Id: If73e73718ecd5db262ed9904091024238f98dbc0 (cherry picked from commit 840644d619e9560f205016eafc8799565ffd6d8c) --- nova/tests/unit/virt/libvirt/test_driver.py | 5 +++-- nova/tests/unit/virt/libvirt/test_utils.py | 3 ++- nova/virt/images.py | 26 ++++++++++++++++++++++++-- nova/virt/libvirt/imagebackend.py | 19 ++++++++++++++----- 4 files changed, 43 insertions(+), 10 deletions(-) diff --git a/nova/tests/unit/virt/libvirt/test_driver.py b/nova/tests/unit/virt/libvirt/test_driver.py index 22ef56d..6fd8728 100644 --- a/nova/tests/unit/virt/libvirt/test_driver.py +++ b/nova/tests/unit/virt/libvirt/test_driver.py @@ -14985,7 +14985,7 @@ class LibvirtVolumeSnapshotTestCase(test.NoDBTestCase): self.mox.VerifyAll() -def _fake_convert_image(source, dest, out_format, +def _fake_convert_image(source, dest, in_format, out_format, run_as_root=True): libvirt_driver.libvirt_utils.files[dest] = '' @@ -15127,7 +15127,8 @@ class LVMSnapshotTests(_BaseSnapshotTests): mock_volume_info.assert_has_calls([mock.call('/dev/nova-vg/lv')]) mock_convert_image.assert_called_once_with( - '/dev/nova-vg/lv', mock.ANY, disk_format, run_as_root=True) + '/dev/nova-vg/lv', mock.ANY, 'raw', disk_format, + run_as_root=True) def test_raw(self): self._test_lvm_snapshot('raw') diff --git a/nova/tests/unit/virt/libvirt/test_utils.py b/nova/tests/unit/virt/libvirt/test_utils.py index 6773bea..6f75a92 100644 --- a/nova/tests/unit/virt/libvirt/test_utils.py +++ b/nova/tests/unit/virt/libvirt/test_utils.py @@ -594,7 +594,8 @@ disk size: 4.4M target = 't.qcow2' self.executes = [] expected_commands = [('qemu-img', 'convert', '-O', 'raw', - 't.qcow2.part', 't.qcow2.converted'), + 't.qcow2.part', 't.qcow2.converted', + '-f', 'qcow2'), ('rm', 't.qcow2.part'), ('mv', 't.qcow2.converted', 't.qcow2')] images.fetch_to_raw(context, image_id, target, user_id, project_id, diff --git a/nova/virt/images.py b/nova/virt/images.py index 5b9374b..e2b5b91 100644 --- a/nova/virt/images.py +++ b/nova/virt/images.py @@ -66,9 +66,31 @@ def qemu_img_info(path): return imageutils.QemuImgInfo(out) -def convert_image(source, dest, out_format, run_as_root=False): +def convert_image(source, dest, in_format, out_format, run_as_root=False): """Convert image to other format.""" + if in_format is None: + raise RuntimeError("convert_image without input format is a security" + "risk") + _convert_image(source, dest, in_format, out_format, run_as_root) + + +def convert_image_unsafe(source, dest, out_format, run_as_root=False): + """Convert image to other format, doing unsafe automatic input format + detection. Do not call this function. + """ + + # NOTE: there is only 1 caller of this function: + # imagebackend.Lvm.create_image. It is not easy to fix that without a + # larger refactor, so for the moment it has been manually audited and + # allowed to continue. Remove this function when Lvm.create_image has + # been fixed. + _convert_image(source, dest, None, out_format, run_as_root) + + +def _convert_image(source, dest, in_format, out_format, run_as_root): cmd = ('qemu-img', 'convert', '-O', out_format, source, dest) + if in_format is not None: + cmd = cmd + ('-f', in_format) utils.execute(*cmd, run_as_root=run_as_root) @@ -123,7 +145,7 @@ def fetch_to_raw(context, image_href, path, user_id, project_id, max_size=0): staged = "%s.converted" % path LOG.debug("%s was %s, converting to raw" % (image_href, fmt)) with fileutils.remove_path_on_error(staged): - convert_image(path_tmp, staged, 'raw') + convert_image(path_tmp, staged, fmt, 'raw') os.unlink(path_tmp) data = qemu_img_info(staged) diff --git a/nova/virt/libvirt/imagebackend.py b/nova/virt/libvirt/imagebackend.py index 5e14f61..151ebc4 100644 --- a/nova/virt/libvirt/imagebackend.py +++ b/nova/virt/libvirt/imagebackend.py @@ -477,7 +477,7 @@ class Raw(Image): self.correct_format() def snapshot_extract(self, target, out_format): - images.convert_image(self.path, target, out_format) + images.convert_image(self.path, target, self.driver_format, out_format) @staticmethod def is_file_in_instance_path(): @@ -631,7 +631,16 @@ class Lvm(Image): size, sparse=self.sparse) if self.ephemeral_key_uuid is not None: encrypt_lvm_image() - images.convert_image(base, self.path, 'raw', run_as_root=True) + # NOTE: by calling convert_image_unsafe here we're + # telling qemu-img convert to do format detection on the input, + # because we don't know what the format is. For example, + # we might have downloaded a qcow2 image, or created an + # ephemeral filesystem locally, we just don't know here. Having + # audited this, all current sources have been sanity checked, + # either because they're locally generated, or because they have + # come from images.fetch_to_raw. However, this is major code smell. + images.convert_image_unsafe(base, self.path, self.driver_format, + run_as_root=True) if resize: disk.resize2fs(self.path, run_as_root=True) @@ -678,8 +687,8 @@ class Lvm(Image): lvm.remove_volumes([self.lv_path]) def snapshot_extract(self, target, out_format): - images.convert_image(self.path, target, out_format, - run_as_root=True) + images.convert_image(self.path, target, self.driver_format, + out_format, run_as_root=True) def get_model(self, connection): return imgmodel.LocalBlockImage(self.path) @@ -786,7 +795,7 @@ class Rbd(Image): self.driver.resize(self.rbd_name, size) def snapshot_extract(self, target, out_format): - images.convert_image(self.path, target, out_format) + images.convert_image(self.path, target, 'raw', out_format) @staticmethod def is_shared_block_storage(): -- 2.5.0