CVE-2012-3361 (published 2012-07-22T16:55Z)

virt/disk/api.py in OpenStack Compute (Nova) Folsom (2012.2), Essex (2012.1), and Diablo (2011.3) allows remote authenticated users to overwrite arbitrary files via a symlink attack on a file in an image.

Severity: MEDIUM
CVSS v2 base score: 5.5 (AV:N/AC:L/Au:S/C:N/I:P/A:P)

Weakness information:
cwe_id: CWE-264
cwe_name: Permissions, Privileges, and Access Controls
description: Weaknesses in this category are related to the management of permissions, privileges, and other security features that are used to perform access control.

Fix information:
repo_url: https://github.com/openstack/nova
commit_details: repo_url: https://github.com/openstack/nova
author: Russell Bryant
author_date: 2012-06-20 11:13:13-04:00
msg: Prevent file injection writing to host filesystem.

Fix bug 1015531, CVE-2012-3360, CVE-2012-3361

This patch prevents the file injection code from writing into the host
filesystem if a user specifies a path for the injected file that
contains '..'.  The check is to make sure that the final normalized path
that is about to be written to is within the mounted guest filesystem.

Signed-off-by: Russell Bryant <rbryant@redhat.com>
Signed-off-by: Pádraig Brady <pbrady@redhat.com>
Signed-off-by: Mark McLoughlin <markmc@redhat.com>

Change-Id: I658cd12fd319cee91eb9544cdf53c862c5d2c560
repository: repo_url: https://github.com/openstack/nova
repo_name: openstack/nova
description: OpenStack Compute (Nova). Mirror of code maintained at opendev.org.
repo_language: Python
owner: openstack
file_changes: filename: test_virt.py
change_type: ModificationType.MODIFY
diff: @@ -15,8 +15,10 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+from nova import exception
 from nova import flags
 from nova import test
+from nova.virt.disk import api as disk_api
 from nova.virt import driver
 
 FLAGS = flags.FLAGS
@@ -81,3 +83,21 @@ class TestVirtDriver(test.TestCase):
                                                 'swap_size': 0}))
         self.assertTrue(driver.swap_is_usable({'device_name': '/dev/sdb',
                                                 'swap_size': 1}))
+
+
+class TestVirtDisk(test.TestCase):
+    def test_check_safe_path(self):
+        ret = disk_api._join_and_check_path_within_fs('/foo', 'etc',
+                                                      'something.conf')
+        self.assertEquals(ret, '/foo/etc/something.conf')
+
+    def test_check_unsafe_path(self):
+        self.assertRaises(exception.Invalid,
+                          disk_api._join_and_check_path_within_fs,
+                          '/foo', 'etc/../../../something.conf')
+
+    def test_inject_files_with_bad_path(self):
+        self.assertRaises(exception.Invalid,
+                          disk_api._inject_file_into_fs,
+                          '/tmp', '/etc/../../../../etc/passwd',
+                          'hax')

programming_language: Python
filename: api.py
change_type: ModificationType.MODIFY
diff: @@ -311,20 +311,39 @@ def inject_data_into_fs(fs, key, net, metadata, admin_password, execute):
         _inject_admin_password_into_fs(admin_password, fs, execute=execute)
 
 
-def _inject_file_into_fs(fs, path, contents):
-    absolute_path = os.path.join(fs, path.lstrip('/'))
+def _join_and_check_path_within_fs(fs, *args):
+    '''os.path.join() with safety check for injected file paths.
+
+    Join the supplied path components and make sure that the
+    resulting path we are injecting into is within the
+    mounted guest fs.  Trying to be clever and specifying a
+    path with '..' in it will hit this safeguard.
+    '''
+    absolute_path = os.path.realpath(os.path.join(fs, *args))
+    if not absolute_path.startswith(os.path.realpath(fs) + '/'):
+        raise exception.Invalid(_('injected file path not valid'))
+    return absolute_path
+
+
+def _inject_file_into_fs(fs, path, contents, append=False):
+    absolute_path = _join_and_check_path_within_fs(fs, path.lstrip('/'))
+
     parent_dir = os.path.dirname(absolute_path)
     utils.execute('mkdir', '-p', parent_dir, run_as_root=True)
-    utils.execute('tee', absolute_path, process_input=contents,
-          run_as_root=True)
+
+    args = []
+    if append:
+        args.append('-a')
+    args.append(absolute_path)
+
+    kwargs = dict(process_input=contents, run_as_root=True)
+
+    utils.execute('tee', *args, **kwargs)
 
 
 def _inject_metadata_into_fs(metadata, fs, execute=None):
-    metadata_path = os.path.join(fs, "meta.js")
     metadata = dict([(m.key, m.value) for m in metadata])
-
-    utils.execute('tee', metadata_path,
-                  process_input=jsonutils.dumps(metadata), run_as_root=True)
+    _inject_file_into_fs(fs, 'meta.js', jsonutils.dumps(metadata))
 
 
 def _inject_key_into_fs(key, fs, execute=None):
@@ -333,20 +352,22 @@ def _inject_key_into_fs(key, fs, execute=None):
     key is an ssh key string.
     fs is the path to the base of the filesystem into which to inject the key.
     """
-    sshdir = os.path.join(fs, 'root', '.ssh')
+    sshdir = _join_and_check_path_within_fs(fs, 'root', '.ssh')
     utils.execute('mkdir', '-p', sshdir, run_as_root=True)
     utils.execute('chown', 'root', sshdir, run_as_root=True)
     utils.execute('chmod', '700', sshdir, run_as_root=True)
-    keyfile = os.path.join(sshdir, 'authorized_keys')
-    key_data = [
+
+    keyfile = os.path.join('root', '.ssh', 'authorized_keys')
+
+    key_data = ''.join([
         '\n',
         '# The following ssh key was injected by Nova',
         '\n',
         key.strip(),
         '\n',
-    ]
-    utils.execute('tee', '-a', keyfile,
-                  process_input=''.join(key_data), run_as_root=True)
+    ])
+
+    _inject_file_into_fs(fs, keyfile, key_data, append=True)
 
 
 def _inject_net_into_fs(net, fs, execute=None):
@@ -354,12 +375,13 @@ def _inject_net_into_fs(net, fs, execute=None):
 
     net is the contents of /etc/network/interfaces.
     """
-    netdir = os.path.join(os.path.join(fs, 'etc'), 'network')
+    netdir = _join_and_check_path_within_fs(fs, 'etc', 'network')
     utils.execute('mkdir', '-p', netdir, run_as_root=True)
     utils.execute('chown', 'root:root', netdir, run_as_root=True)
     utils.execute('chmod', 755, netdir, run_as_root=True)
-    netfile = os.path.join(netdir, 'interfaces')
-    utils.execute('tee', netfile, process_input=net, run_as_root=True)
+
+    netfile = os.path.join('etc', 'network', 'interfaces')
+    _inject_file_into_fs(fs, netfile, net)
 
 
 def _inject_admin_password_into_fs(admin_passwd, fs, execute=None):
@@ -384,16 +406,15 @@ def _inject_admin_password_into_fs(admin_passwd, fs, execute=None):
     fd, tmp_shadow = tempfile.mkstemp()
     os.close(fd)
 
-    utils.execute('cp', os.path.join(fs, 'etc', 'passwd'), tmp_passwd,
-                  run_as_root=True)
-    utils.execute('cp', os.path.join(fs, 'etc', 'shadow'), tmp_shadow,
-                  run_as_root=True)
+    passwd_path = _join_and_check_path_within_fs(fs, 'etc', 'passwd')
+    shadow_path = _join_and_check_path_within_fs(fs, 'etc', 'shadow')
+
+    utils.execute('cp', passwd_path, tmp_passwd, run_as_root=True)
+    utils.execute('cp', shadow_path, tmp_shadow, run_as_root=True)
     _set_passwd(admin_user, admin_passwd, tmp_passwd, tmp_shadow)
-    utils.execute('cp', tmp_passwd, os.path.join(fs, 'etc', 'passwd'),
-                  run_as_root=True)
+    utils.execute('cp', tmp_passwd, passwd_path, run_as_root=True)
     os.unlink(tmp_passwd)
-    utils.execute('cp', tmp_shadow, os.path.join(fs, 'etc', 'shadow'),
-                  run_as_root=True)
+    utils.execute('cp', tmp_shadow, shadow_path, run_as_root=True)
     os.unlink(tmp_shadow)
 
 

programming_language: Python