Fix EOFError in sam plugin on empty lm/nt hash

[JazzCore]

Met a strange Win10 machine with account that has LM and NTLM hashes buffers with zero size:

<user_V ... lmpw_ofs=0x1a4, lmpw_len=0x0, unknownc_1=0x0, ntpw_ofs=0x1bc, ntpw_len=0x0, unknownd_1=0x0, unknownd_2=0x1d4, unknownd_3=0x18, unknownd_4=0x0, unknownd_5=0x1ec, unknownd_6=0x18, unknownd_7=0x0, data=b'\x01\x00\x14\x80'>

target-query throws following exception:

  File "/home/user/.local/bin/target-query", line 8, in <module>
    sys.exit(main())
             ^^^^^^
  File "/home/user/.local/lib/python3.11/site-packages/dissect/target/tools/utils.py", line 250, in wrapper
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/.local/lib/python3.11/site-packages/dissect/target/tools/query.py", line 371, in main
    raise e
  File "/home/user/.local/lib/python3.11/site-packages/dissect/target/tools/query.py", line 356, in main
    for record_entries in entry:
  File "/home/user/.local/lib/python3.11/site-packages/dissect/target/plugins/os/windows/sam.py", line 391, in sam
    lm_hash = decrypt_single_hash(f.rid, samkey, u_lmpw, almpassword).hex()
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/.local/lib/python3.11/site-packages/dissect/target/plugins/os/windows/sam.py", line 255, in decrypt_single_hash
    sh = c_sam.SAM_HASH(enc_hash)
         ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/.local/lib/python3.11/site-packages/dissect/cstruct/types/base.py", line 24, in __call__
    return self.read(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/.local/lib/python3.11/site-packages/dissect/cstruct/types/base.py", line 71, in read
    return self.reads(obj)
           ^^^^^^^^^^^^^^^
  File "/home/user/.local/lib/python3.11/site-packages/dissect/cstruct/types/base.py", line 43, in reads
    return self._read(BytesIO(data))
           ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "<compiled SAM_HASH>", line 15, in _read
EOFError

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[Schamper]

Might be nicer to put something like this in the decrypt_single_hash function itself:

if not enc_hash:
    return b""

That way you don't have to do this if twice and it's more fault-tolerant for future uses.

[JazzCore]

Sure, fixed

[JazzCore]

@DissectBot agree

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (fb44232) 73.99% compared to head (3eeb6b3) 73.99%.

Files	Patch %	Lines
dissect/target/plugins/os/windows/sam.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #478      +/-   ##
==========================================
- Coverage   73.99%   73.99%   -0.01%     
==========================================
  Files         260      260              
  Lines       21064    21066       +2     
==========================================
+ Hits        15587    15588       +1     
- Misses       5477     5478       +1     

Flag	Coverage Δ
unittests	73.99% <50.00%> (-0.01%)	⬇️

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