Segfault for ntlm_seal when no confidentiality or integrity is negotiated

[jborean93]

If trying to wrap data when neither the sign or seal negotiate flags were negotiated then gss_wrap will seg fault. The same scenario through SSPI has the EncryptMessage function return SEC_E_UNSUPPORTED_FUNCTION and I would expect a similar result here and not a fatal error.

To reproduce run the following

import gssapi
import os
import tempfile

ntlm = gssapi.OID.from_int_seq('1.3.6.1.4.1.311.2.2.10')

with tempfile.NamedTemporaryFile() as temp_fd:
    with open(temp_fd.name, mode='wb') as fd:
        fd.write(b"DOMAIN:USER:PASS")

    os.environ['NTLM_USER_FILE'] = temp_fd.name

    c_cred = gssapi.Credentials(name=gssapi.Name(base='DOMAIN\\USER', name_type=gssapi.NameType.user), usage='initiate', mechs=[ntlm])
    s_cred = gssapi.Credentials(usage='accept', mechs=[ntlm])

    spn = gssapi.Name(base='http@test', name_type=gssapi.NameType.hostbased_service)
    c = gssapi.SecurityContext(creds=c_cred, usage='initiate', name=spn, mech=ntlm, flags=gssapi.RequirementFlag.mutual_authentication)
    s = gssapi.SecurityContext(creds=s_cred, usage='accept')

    c.step(s.step(c.step()))

    c.wrap(b"data", True)

When stepping through the code the seg fault seems to happen in https://github.com/gssapi/gss-ntlmssp/blob/a14a99672c81fe2d0eebb71edd86055ad190e417/src/ntlm_crypto.c#L870 as the seal_handle has not been generated due to sign/seal not being set.

Sorry for the massive influx of questions/problems here, just trying to report what I can see when doing tests.