security: check if shared memory belongs to current user and is only … #43
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…read/writeable for them
Prevents
1. information disclosure
2. unpickling of untrusted pickle files resulting in code execution
vulnerabilities
Execute as user `nobody`:
```
$ python3
>>> with open('/dev/shm/sm_foo', 'wb') as fd:
... fd.write(b'\x80\x03csubprocess\ncall\nq\x00X\n\x00\x00\x00/bin/touchq\x01X\x0b\x00\x00\x00/tmp/hackedq\x02\x86q\x03\x85q\x04Rq\x05.')
...
66
$ ls -l '/dev/shm/sm_foo'
-rw-r--r-- 1 nobody nogroup 66 Okt 21 18:42 /dev/shm/sm_foo
```
Then execute a new process as any user (e.g. root):
```
$ python3
>>> import shared_memory_dict
>>> f = shared_memory_dict.SharedMemoryDict('foo', 500)
>>> f
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/home/fbest/git/shared-memory-dict/shared_memory_dict/dict.py", line 115, in __repr__
return repr(self._read_memory())
File "/home/fbest/git/shared-memory-dict/shared_memory_dict/dict.py", line 169, in _read_memory
db = {key: self._unmap_value(key, value) for key, value in db.items()}
AttributeError: 'int' object has no attribute 'items'
$ ls -l /tmp/hacked
-rw-r--r-- 1 root root 0 Okt 21 18:45 /tmp/hacked
```
The command /bin/touch /tmp/hacked has been executed as root.
Fixes luizalabs#33
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…read/writeable for them
Fixes #33