struct.error when processing an mp4 file

[jvoisin]

When running the following python script with the attached file, mutagen throws a struct.error exception:

import mutagen, sys

f = mutagen.File(sys.argv[1])
f.delete()

$  python3 mutest.py crash-116c56788bf36e630a7ab5c43bdd6e55b2ee2e0b706f5493dfb7a22e1ac1c81f
Traceback (most recent call last):
  File "mutest.py", line 4, in <module>
    f.delete()
  File "/home/jvoisin/app/AFL/ven/lib/python3.7/site-packages/mutagen/_util.py", line 140, in wrapper
    return func(self, h, *args, **kwargs)
  File "/home/jvoisin/app/AFL/ven/lib/python3.7/site-packages/mutagen/_file.py", line 120, in delete
    return self.tags.delete(filething)
  File "/home/jvoisin/app/AFL/ven/lib/python3.7/site-packages/mutagen/mp4/__init__.py", line 836, in delete
    self.save(filename, padding=lambda x: 0)
  File "/home/jvoisin/app/AFL/ven/lib/python3.7/site-packages/mutagen/_util.py", line 169, in wrapper
    return func(*args, **kwargs)
  File "/home/jvoisin/app/AFL/ven/lib/python3.7/site-packages/mutagen/_util.py", line 140, in wrapper
    return func(self, h, *args, **kwargs)
  File "/home/jvoisin/app/AFL/ven/lib/python3.7/site-packages/mutagen/mp4/__init__.py", line 425, in save
    self.__save(filething.fileobj, atoms, data, padding)
  File "/home/jvoisin/app/AFL/ven/lib/python3.7/site-packages/mutagen/mp4/__init__.py", line 433, in __save
    self.__save_existing(fileobj, atoms, path, data, padding)
  File "/home/jvoisin/app/AFL/ven/lib/python3.7/site-packages/mutagen/mp4/__init__.py", line 498, in __save_existing
    self.__update_parents(fileobj, path[:-1], delta)
  File "/home/jvoisin/app/AFL/ven/lib/python3.7/site-packages/mutagen/mp4/__init__.py", line 517, in __update_parents
    fileobj.write(cdata.to_uint_be(size + delta))
struct.error: argument out of range
zsh: exit 1     python3 mutest.py 
$

[lazka]

Just for some context: Are these all real files or the result of fuzzing?

[jvoisin]

It's the result of fuzzing :)

[lazka]

ok, cool, thanks. Just asking since if the files were real we'd have to check how other software parses them and try to still load them instead of just erroring out in a controlled way.

[jvoisin]

Oh, right, my bad, I should have thought about this. They are all randomly generated, and entirely invalid. The right way™ to handle them in my opinion is to raise an exception like mutagen.MutagenError or ValueError :)

[phw]

It's worth noting that the actual issue can no longer be reproduced directly with the provided file since it raises a controlled exception on loading after the fixes in #429.

But I think the proposed fix in #462 of handling this case is still valid, though.

[phw]

Fixed in #462