[Bug 1884265] Re: [fips] ntpq segfaults when attempting to use MD5 from FIPS-openssl library.

[Marc Deslauriers]

ACK on the debdiff in comment #11, uploaded with a slight LP tag fix for
processing by the SRU team. Thanks!

** Changed in: openssl (Ubuntu Bionic)
       Status: Confirmed => In Progress

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Title:
  [fips] ntpq segfaults when attempting to use MD5 from FIPS-openssl
  library.

Status in openssl package in Ubuntu:
  In Progress
Status in openssl source package in Bionic:
  In Progress

Bug description:
  [Impact]
  In FIPS mode on Bionic MD5 is semi-disabled causing some applications to segfault.

  ntpq uses crypto hashes to authenticate its requests. By default it
  uses md5. However, when compiled with openssl it creates a lists of
  acceptable hashes from openssl that can be used.

  This issue is only applicable in bionic and when using fips-openssl.

  [Test Steps]
  Test case:
  sudo apt install ntp
  ntpq -p
  Segmentation fault (core dumped)

  What happens there is ntpq wants to iterate all available digests
  (list_digest_names in ntpq.c). It uses EVP_MD_do_all_sorted for this
  task.

  EVP_MD_do_all_sorted eventually runs openssl_add_all_digests_int in c_alld.c.
  For FIPS mode it adds:
  EVP_add_digest(EVP_md5());

  What happens later in ntpq is (list_md_fn function inside ntpq.c):
  ctx = EVP_MD_CTX_new();
  EVP_DigestInit(ctx, EVP_get_digestbyname(name));
  EVP_DigestFinal(ctx, digest, &digest_len);

  First digest it gets is MD5, but while running EVP_DigestInit for it, it gets to this point (openssl/crypto/evp/digest.c EVP_DigestInit_ex):
  #ifdef OPENSSL_FIPS
          if (FIPS_mode()) {
              if (!(type->flags & EVP_MD_FLAG_FIPS)
                  && !(ctx->flags & EVP_MD_CTX_FLAG_NON_FIPS_ALLOW)) {
                  EVPerr(EVP_F_EVP_DIGESTINIT_EX, EVP_R_DISABLED_FOR_FIPS);
                  return 0;
              }
          }
  #endif

  Due to type->flags for MD5 being 0 there's an error set (EVP_R_DISABLED_FOR_FIPS).
  After getting back to ntpq.c:
  ctx->engine and ctx->digest are not set (due to the mentioned error), hence

  inside EVP_DigestFinal_ex (openssl/crypto/evp/digest.c)
  OPENSSL_assert(ctx->digest->md_size <= EVP_MAX_MD_SIZE);
  causes a segfault (ctx->digest is NULL).

  So either MD5 shouldn't be added in FIPS mode or it should have the
  EVP_MD_FLAG_FIPS to be properly initialized.

  [Regression Potential]

  I don't think this should regress ntpq + openssl from the Ubuntu
  archive.

  Current archive ntpq + openssl behaviour:
  openssl includes all message digests and hands ntpq a sorted digest-list.
  ntpq doesn't check return from EVP_Digest(Init|Final) and assumes all is well and sticks all digests into its list regardless if it is working or not.

  i.e.
  ntpq> help keytype
  function: set key type to use for authenticated requests, one of:
      MD4, MD5, RIPEMD160, SHA1, SHAKE128

  If somehow openssl library is corrupted and sends back erroneous
  results, its possible the authentication will just not ever work.

  Newly fixed archive ntpq + oenssl beahviour:
  openssl includes all message digests and hands ntpq a sorted digest-list.
  ntpq checks each one and includes each working digest. With a non-corrupted openssl, everything works fine and ntpq includes each into its list. Ends up with a list identical to the one above.

  If somehow opensll library is corrupted and sends back erroneous
  results, ntpq will hopefully catch it by checking return code and
  include only those algos that appear to be working. Its possible
  authentication will work for ntpq.

  The difference will be seen in ntpq + fips-openssl. ntpq will check
  return, and for fips-not-approved algos, return will indicate an
  error. So these algos will be skipped and ntpq will not include into
  its digest list. Resulting in a much shorter list of only fips-
  approved algos.

  i.e.
  ntpq> help keytype
  function: set key type to use for authenticated requests, one of:
      SHA1, SHAKE128

  Since md5 is ntpq's default auth algo, this will need to be changed to one of the above algos in the config files.
  But I think it is somewhat understood that MD5 is bad in a FIPS environment.

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