Optimize the handling of problematic files

libmat2/abstract.py

 import abc
 import os
+import re
 from typing import Set, Dict, Union
 
 assert Set  # make pyflakes happy
@@ -17,6 +18,11 @@ class AbstractParser(abc.ABC):
         """
         :raises ValueError: Raised upon an invalid file
         """
+        if re.search('^[a-z0-9./]', filename) is None:
+            # Some parsers are calling external binaries,
+            # this prevents shell command injections
+            filename = os.path.join('.', filename)
+
         self.filename = filename
         fname, extension = os.path.splitext(filename)
         self.output_filename = fname + '.cleaned' + extension

libmat2/exiftool.py

 import json
 import os
-import re
-import shutil
 import subprocess
-import tempfile
-
-from typing import Dict, Union, Set, Callable, Any
+from typing import Dict, Union, Set
 
 from . import abstract
 
@@ -20,23 +16,8 @@ class ExiftoolParser(abstract.AbstractParser):
     """
     meta_whitelist = set()  # type: Set[str]
 
-    def _handle_problematic_filename(self, callback: Callable[[str], Any]) -> bytes:
-        """ This method takes a filename with a potentially problematic name,
-        and safely applies a `callback` to it.
-        """
-        if re.search('^[a-z0-9/]', self.filename) is not None:
-            return callback(self.filename)
-
-        tmpdirname = tempfile.mkdtemp()
-        fname = os.path.join(tmpdirname, "temp_file")
-        shutil.copy(self.filename, fname)
-        out = callback(fname)
-        shutil.rmtree(tmpdirname)
-        return out
-
     def get_meta(self) -> Dict[str, Union[str, dict]]:
-        fun = lambda f: subprocess.check_output([_get_exiftool_path(), '-json', f])
-        out = self._handle_problematic_filename(fun)
+        out = subprocess.check_output([_get_exiftool_path(), '-json', self.filename])
         meta = json.loads(out.decode('utf-8'))[0]
         for key in self.meta_whitelist:
             meta.pop(key, None)

libmat2/video.py

@@ -24,10 +24,9 @@ class AVIParser(exiftool.ExiftoolParser):
                       'SampleRate', 'AvgBytesPerSec', 'BitsPerSample',
                       'Duration', 'ImageSize', 'Megapixels'}
 
-
-    def __remove_all_internal(self, filename: str):
+    def remove_all(self):
         cmd = [_get_ffmpeg_path(),
-               '-i', filename,           # input file
+               '-i', self.filename,           # input file
                '-y',                     # overwrite existing output file
                '-loglevel', 'panic',     # Don't show log
                '-hide_banner',           # hide the banner
@@ -38,11 +37,8 @@ class AVIParser(exiftool.ExiftoolParser):
                '-flags:v', '+bitexact',  # don't add any metadata
                '-flags:a', '+bitexact',  # don't add any metadata
                self.output_filename]
-        subprocess.check_call(cmd)
-
-    def remove_all(self) -> bool:
         try:
-            self._handle_problematic_filename(self.__remove_all_internal)
+            subprocess.check_call(cmd)
         except subprocess.CalledProcessError as e:
             logging.error("Something went wrong during the processing of %s: %s", self.filename, e)
             return False

tests/test_corrupted_files.py

@@ -204,3 +204,14 @@ class TestCorruptedFiles(unittest.TestCase):
         p = video.AVIParser('./tests/data/clean.avi')
         self.assertFalse(p.remove_all())
         os.remove('./tests/data/clean.avi')
+
+    def test_avi_injection(self):
+        try:
+            video._get_ffmpeg_path()
+        except RuntimeError:
+            raise unittest.SkipTest
+
+        shutil.copy('./tests/data/dirty.torrent', './tests/data/--output.avi')
+        p = video.AVIParser('./tests/data/--output.avi')
+        self.assertFalse(p.remove_all())
+        os.remove('./tests/data/--output.avi')

tests/test_libmat2.py

@@ -46,10 +46,23 @@ class TestParameterInjection(unittest.TestCase):
         shutil.copy('./tests/data/dirty.avi', './--output')
         p = video.AVIParser('--output')
         meta = p.get_meta()
-        print(meta)
         self.assertEqual(meta['Software'], 'MEncoder SVN-r33148-4.0.1')
         os.remove('--output')
 
+    def test_ffmpeg_injection_complete_path(self):
+        try:
+            video._get_ffmpeg_path()
+        except RuntimeError:
+            raise unittest.SkipTest
+
+        shutil.copy('./tests/data/dirty.avi', './tests/data/ --output.avi')
+        p = video.AVIParser('./tests/data/ --output.avi')
+        meta = p.get_meta()
+        self.assertEqual(meta['Software'], 'MEncoder SVN-r33148-4.0.1')
+        self.assertTrue(p.remove_all())
+        os.remove('./tests/data/ --output.avi')
+        os.remove('./tests/data/ --output.cleaned.avi')
+
 
 class TestUnsupportedEmbeddedFiles(unittest.TestCase):
     def test_odt_with_svg(self):