Fix reading for long MakerNote and UserComment #165
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Lessica
commented
Apr 5, 2022
exifread/classes.py
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| values = self._process_field2(ifd_name, tag_name, count, offset) | ||
| else: | ||
| elif field_type == 7: # undefined | ||
| values = self._process_field7(ifd_name, tag_name, count, offset) |
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It's better not to handle data format 7 (undefined) type in function _process_field, which is used to parse signed/unsigned numbers.
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That's why I moved this special case into another function _process_field7.
Lessica
commented
Apr 5, 2022
| # XXX investigate | ||
| # some entries get too big to handle could be malformed | ||
| # file or problem with self.s2n | ||
| if count < 1000: |
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We cannot just ignore large entries other than MakerNote.
Lessica
commented
Apr 5, 2022
| offset = offset + type_length | ||
| # The test above causes problems with tags that are | ||
| # supposed to have long values! Fix up one important case. | ||
| elif tag_name in ('MakerNote', makernote.canon.CAMERA_INFO_TAG_NAME): |
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Moved to function _process_field7.
Lessica
commented
Apr 5, 2022
| @@ -97,6 +97,8 @@ def s2n(self, offset, length: int, signed=False) -> int: | |||
| raise ValueError('unexpected unpacking length: %d' % length) from err | |||
| self.file_handle.seek(self.offset + offset) | |||
| buf = self.file_handle.read(length) | |||
| if len(buf) != length: | |||
| raise ValueError("cannot read enough bytes, something elsewhere is wrong") | |||
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This prevents infinite loop in some tests. But it will not be fixed until the parsing of Canon's MakerNote being fixed.
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This requires further investigation.
Keep raw values for undefined types e.g. `MakerNote` and `UserComment`
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Top-level large entries (e.g. MakerNote and UserComment) are usually in data format 7 (unspecified). See: http://www.fifi.org/doc/jhead/exif-e.html#DataForm
We should simply ignore its length, read and keep its original values for further use.
But
IfdTagentries insideMakerNotestill have problems, which requires further investigation.