Respect ace_count while unpacking ACEs

[MWedl]

AclPacket._unpack_aces() does not respect the ace_count field. This method keeps parsing ACEs until there is no data left in the buffer. Most of the time this works fine, because normally there is no data after ace_count ACEs. However, while unpacking DACLs of IPC$ shares there is data left. This causes _unpack_aces to crash or sometimes to run into endless loops. I don't know what the exceeding data after the ACEs is, nor have I found any documentation about it, but they are certainly no ACEs.

Example:

AclPacket:
  acl_revision: 0x02
  sbz1: 0x00
  acl_size: 0x0408 (size of 3 ACEs + exceeding data at end)
  ace_count: 0x0003
  sbz2: 0x0000
  aces: 3 valid ACEs (total size of all 3 ACEs: 60 bytes)
  exceeding unknown data (964 bytes)

[jborean93]

The change is fine but I'm wondering whether it's possible to add a test to unpack your data to https://github.com/jborean93/smbprotocol/blob/master/tests/test_security_descriptor.py. This will ensure that this mistake isn't made again in the future if the code is ever changed.

[MWedl]

Thanks for the feedback. I have added a test case.

[codecov]

Codecov Report

Merging #143 (fb2257c) into master (1f1b52a) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #143   +/-   ##
=======================================
  Coverage   98.91%   98.91%           
=======================================
  Files          23       23           
  Lines        4989     4989           
=======================================
  Hits         4935     4935           
  Misses         54       54           

Impacted Files	Coverage Δ
smbprotocol/security_descriptor.py	100.00% <100.00%> (ø)

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[jborean93]

Thanks for adding the test, it's much appreciated.