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Commit62fb5ba

Browse files
committed
More work on#2
Tidied up the handling of invalid sectors in the DIFAT; special valuesnow always terminate the DIFAT and FREE_SECTOR is no longer a warning asa terminator (the AAF spec is rather ambiguous on this point but it'sworth following the de-facto standard practice)
1 parent8bc177c commit62fb5ba

9 files changed

+74
-17
lines changed

‎compoundfiles/reader.py

Lines changed: 15 additions & 17 deletions
Original file line numberDiff line numberDiff line change
@@ -357,7 +357,8 @@ def _load_master_fat(self):
357357
# Note: when reading the master-FAT we deliberately disregard the
358358
# master-FAT sector count read from the header as implementations may
359359
# set this incorrectly. Instead, we scan for END_OF_CHAIN (or
360-
# FREE_SECTOR) in the DIFAT after each read and stop when we find it. # In order to avoid infinite loops (in the case of a stupid or
360+
# FREE_SECTOR) in the DIFAT after each read and stop when we find it.
361+
# In order to avoid infinite loops (in the case of a stupid or
361362
# malicious file) we keep track of each sector we seek to and quit in
362363
# the event of a repeat
363364
self._master_fat=array(native_str('L'))
@@ -392,24 +393,21 @@ def _load_master_fat(self):
392393
# Check for an END_OF_CHAIN marker in the existing stream
393394
forindexinrange(checked,len(self._master_fat)):
394395
value=self._master_fat[index]
395-
ifvalue==END_OF_CHAIN:
396-
break
397-
elifvalue==FREE_SECTOR:
398-
warnings.warn(
399-
CompoundFileMasterFatWarning(
400-
'DIFAT terminated by FREE_SECTOR'))
401-
value=END_OF_CHAIN
402-
break
403-
elifself._max_sector<value<=MAX_NORMAL_SECTOR:
404-
warnings.warn(
405-
CompoundFileMasterFatWarning(
406-
'sector in DIFAT chain beyond file end (%d)'%value))
396+
ifvalue>self._max_sector:
397+
ifvaluein (END_OF_CHAIN,FREE_SECTOR):
398+
pass
399+
elifvalue>MAX_NORMAL_SECTOR:
400+
warnings.warn(
401+
CompoundFileMasterFatWarning(
402+
'DIFAT terminated by invalid special '
403+
'value (%d)'%value))
404+
else:
405+
warnings.warn(
406+
CompoundFileMasterFatWarning(
407+
'sector in DIFAT chain beyond file '
408+
'end (%d)'%value))
407409
value=END_OF_CHAIN
408410
break
409-
elifvalue>MAX_NORMAL_SECTOR:
410-
warnings.warn(
411-
CompoundFileMasterFatWarning(
412-
'invalid special value in DIFAT chain (%d)'%value))
413411
ifvalue==END_OF_CHAIN:
414412
delself._master_fat[index:]
415413
break

‎tests/invalid_master_eof.dat

3 KB
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‎tests/invalid_master_loop.dat

60.5 KB
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‎tests/invalid_master_overrun.dat

60.5 KB
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‎tests/invalid_master_special.dat

3 KB
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‎tests/invalid_master_underrun.dat

60.5 KB
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‎tests/strange_master_ext.dat

60.5 KB
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‎tests/strange_master_full.dat

60.5 KB
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‎tests/test_function.py

Lines changed: 59 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -302,6 +302,22 @@ def test_invalid_dir_sector_count():
302302
assertlen(w)==1
303303
verify_example(doc)
304304

305+
deftest_invalid_master_sectors():
306+
withwarnings.catch_warnings(record=True)asw:
307+
# Same as example.dat with second master FAT block pointing beyond EOF;
308+
# reader ignores it and all further blocks
309+
withcf.CompoundFileReader('tests/invalid_master_eof.dat')asdoc:
310+
assertissubclass(w[0].category,cf.CompoundFileMasterFatWarning)
311+
assertlen(w)==1
312+
verify_example(doc)
313+
withwarnings.catch_warnings(record=True)asw:
314+
# Same as example.dat with second master FAT block set to
315+
# MASTER_FAT_SECTOR; reader ignores it and all further blocks
316+
withcf.CompoundFileReader('tests/invalid_master_special.dat')asdoc:
317+
assertissubclass(w[0].category,cf.CompoundFileMasterFatWarning)
318+
assertlen(w)==1
319+
verify_example(doc)
320+
305321
deftest_invalid_master_ext():
306322
withwarnings.catch_warnings(record=True)asw:
307323
# Same as example.dat with master FAT extension pointer set to
@@ -376,6 +392,49 @@ def test_strange_mini_sector_size():
376392
assertlen(w)==1
377393
verify_example(doc)
378394

395+
deftest_strange_master_full():
396+
# Same as example.dat with FAT extended to include enough blank sectors to
397+
# fill the DIFAT without an extension (e.g. a compound document where lots
398+
# of contents have been deleted and the FAT hasn't been compressed but
399+
# simply overwritten)
400+
withwarnings.catch_warnings(record=True)asw:
401+
withcf.CompoundFileReader('tests/strange_master_full.dat')asdoc:
402+
assertlen(w)==0
403+
verify_example(doc)
404+
405+
deftest_strange_master_ext():
406+
# Same as example.dat with FAT extended to include enough blank sectors to
407+
# necessitate a DIFAT extension (e.g. a compound document where lots of
408+
# contents have been deleted and the FAT hasn't been compressed but simply
409+
# overwritten)
410+
withwarnings.catch_warnings(record=True)asw:
411+
withcf.CompoundFileReader('tests/strange_master_ext.dat')asdoc:
412+
assertlen(w)==0
413+
verify_example(doc)
414+
415+
deftest_invalid_master_loop():
416+
withpytest.raises(cf.CompoundFileMasterLoopError):
417+
# Same as strange_master_ext.dat but with DIFAT extension sector filled
418+
# and terminated with a self-reference
419+
doc=cf.CompoundFileReader('tests/invalid_master_loop.dat')
420+
421+
deftest_invalid_master_len():
422+
withwarnings.catch_warnings(record=True)asw:
423+
# Same as strange_master_ext.dat with master extension count set to 2
424+
# (should be 1); reader ignores DIFAT count
425+
withcf.CompoundFileReader('tests/invalid_master_underrun.dat')asdoc:
426+
assertissubclass(w[0].category,cf.CompoundFileMasterFatWarning)
427+
assertlen(w)==1
428+
verify_example(doc)
429+
withwarnings.catch_warnings(record=True)asw:
430+
# Same as strange_master_ext.dat with master extension count set to 0
431+
# (should be 1); reader ignores DIFAT count
432+
withcf.CompoundFileReader('tests/invalid_master_overrun.dat')asdoc:
433+
assertissubclass(w[0].category,cf.CompoundFileMasterFatWarning)
434+
assertissubclass(w[1].category,cf.CompoundFileMasterFatWarning)
435+
assertlen(w)==2
436+
verify_example(doc)
437+
379438
deftest_stream_attr():
380439
withcf.CompoundFileReader('tests/example.dat')asdoc:
381440
withdoc.open('Storage 1/Stream 1')asf:

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