pySim-shell: don't get trapped in applications without file system

When we traverse the file system, we may also end up selecting
applications (ADF), which do not support an USIM/ISIM like file system.
This will leave us without the ability to select the MF (or any other
file) again. The only way out is to select the ISIM or USIM application
again to get the access to the file system again.

Change-Id: Ia2fdd65f430c07acb1afdaf265d24c6928b654e0
Related: OS#5418
---
M pySim-shell.py
1 file changed, 43 insertions(+), 2 deletions(-)

diff --git a/pySim-shell.py b/pySim-shell.py
index 3d8bd86..6ff484b 100755
--- a/pySim-shell.py
+++ b/pySim-shell.py
@@ -54,7 +54,7 @@
 from pySim.utils import is_hexstr_or_decimal, is_hexstr, is_decimal
 from pySim.card_handler import CardHandler, CardHandlerAuto
 
-from pySim.filesystem import CardDF, CardADF
+from pySim.filesystem import CardMF, CardDF, CardADF
 from pySim.ts_102_222 import Ts102222Commands
 from pySim.gsm_r import DF_EIRENE
 from pySim.cat import ProactiveCommand
@@ -518,7 +518,32 @@
                 # below, so we must not move up.
                 if skip_df == False:
                     self.walk(indent + 1, action_ef, action_df, context, **kwargs)
-                    fcp_dec = self._cmd.lchan.select("..", self._cmd)
+
+                    parent = self._cmd.lchan.selected_file.parent
+                    df = self._cmd.lchan.selected_file
+                    adf = self._cmd.lchan.selected_adf
+                    if isinstance(parent, CardMF) and (adf and adf.has_fs == False):
+                        # Not every application that may be present on a GlobalPlatform card will support the SELECT
+                        # command as we know it from ETSI TS 102 221, section 11.1.1. In fact the only subset of
+                        # SELECT we may rely on is the OPEN SELECT command as specified in GlobalPlatform Card
+                        # Specification, section 11.9. Unfortunately the OPEN SELECT command only supports the
+                        # "select by name" method, which means we can only select an application and not a file.
+                        # The consequence of this is that we may get trapped in an application that does not have
+                        # ISIM/USIM like file system support and the only way to leave that application is to select
+                        # an ISIM/USIM application in order to get the file system access back.
+                        #
+                        # To automate this escape-route while traversing the file system we will check whether
+                        # the parent file is the MF. When this is the case and the selected ADF has no file system
+                        # support, we will select an arbitrary ADF that has file system support first and from there
+                        # we will then select the MF.
+                        for selectable in parent.get_selectables().items():
+                            if isinstance(selectable[1], CardADF) and selectable[1].has_fs == True:
+                                self._cmd.lchan.select(selectable[1].name, self._cmd)
+                                break
+                        self._cmd.lchan.select(df.get_mf().name, self._cmd)
+                    else:
+                        # Normal DF/ADF selection
+                        fcp_dec = self._cmd.lchan.select("..", self._cmd)
 
             elif action_ef:
                 df_before_action = self._cmd.lchan.selected_file

