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.

This is a backport of Russell Bryant, Pádraig Brady and Mark
McLoughlin's Folsom patch.

Change-Id: Id8bd6ffb4d878467ba2086d341fce23f2ff5aa0a

Author: ttx

nova/tests/test_virt.py

@@ -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 @@ def test_swap_is_usable(self):
                                                 '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')

nova/virt/disk/api.py

@@ -306,20 +306,39 @@ 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=json.dumps(metadata), run_as_root=True)
+    _inject_file_into_fs(fs, 'meta.js', json.dumps(metadata))
 
 
 def _inject_key_into_fs(key, fs, execute=None):
@@ -328,33 +347,36 @@ 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):
     """Inject /etc/network/interfaces into the filesystem rooted at fs.
 
     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):
@@ -379,16 +401,15 @@ 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)