[Bug 1835135] Re: FIPS OpenSSL crashes Python2 hashlib

[Joy Latten]

The assessment is accurate.

FIPS 140-2 does not allow MD5 except for use in PRF.

Thus the  OpenSSL_add_all_digests in fips openssl does not include MD5. However, SSL_library_init() does include MD5 but only for use in calculating the PRF. Notice in tls1_P_hash() in ssl/t1_enc.c
the flag, EVP_MD_CTX_FLAG_NON_FIPS_ALLOW, is set in the context to permit this use of MD5.
Apps wishing to calculate their own PRF can do the same.

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Title:
  FIPS OpenSSL crashes Python2 hashlib

Status in python2.7 package in Ubuntu:
  Triaged

Bug description:
  If Ubuntu/Canonical's FIPS-compliant OpenSSL is initialized with
  SSL_library_init, then Python2's hashlib bindings for MD5 can trigger
  a SIGSEGV via a NULL pointer dereference (if calling the .update
  method) or a SIGABRT (if passing input to the constructor or passing
  no input and invoking the .final method). This happens if, for
  example, PyOpenSSL is imported before hashlib.

  Canonical's FIPS patches for OpenSSL introduce some odd behavior that
  arguably should be revisited, but the (TL;DR) core bug is that Python2
  hashlib doesn't properly check the return value of EVP_DigestInit,
  preventing hashlib from falling back to it's internal MD5
  implementation and instead setting things up for use of the MD5
  context to trigger SIGSEGV or SIGABRT.

  Python3 correctly checks the return value, so the fix is to backport
  the relevant code into Python2 (see
  python2.7-2.7.12/Modules/_hashopenssl.c).

  See attached good.py and bad.py files which exhibit the import order-
  dependent crashing issue. See attached fips-md5-python-init-bug.c
  which shows the FIPS OpenSSL behaviors that conditionally tickle the
  Python2 bug. The C file also contains a much more detailed description
  of the Python2 bug and other behavior which I'd rather not repeat
  here.

  I discovered this bug investigating an issue with the third-party apt-
  boto-s3 package. See https://github.com/boto/boto3/issues/2021

  Note that this bug effects Splunk, Inc, which has a corporate Ubuntu
  Advantage license. My login account is attached to a different,
  single-seat license.

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