[Bug 1906627] Re: GSS-SPNEGO implementation in cyrus-sasl2 is incompatible with Active Directory, causing recent adcli regression

[Matthew Ruffell]

Attached is option one: a debdiff for adcli, which builds on
0.8.2-1ubuntu1 and simply adds a depends to the fixed libsasl2-modules-
gssapi-mit at greater or equal to relationship. This will require the
0.8.2-1ubuntu2 package in -unapproved queue to be deleted.

** Patch added: "debdiff for adcli on Bionic"
   https://bugs.launchpad.net/ubuntu/+source/adcli/+bug/1906627/+attachment/5441872/+files/lp1906627_adcli_option_one.debdiff

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Title:
  GSS-SPNEGO implementation in cyrus-sasl2 is incompatible with Active
  Directory, causing recent adcli regression

Status in adcli package in Ubuntu:
  Fix Released
Status in cyrus-sasl2 package in Ubuntu:
  Fix Released
Status in adcli source package in Bionic:
  In Progress
Status in cyrus-sasl2 source package in Bionic:
  In Progress

Bug description:
  [Impact]

  A recent release of adcli 0.8.2-1ubuntu1 to bionic-updates caused a
  regression for some users when attempting to join a Active Directory
  realm. adcli introduced a default behaviour change, moving from GSS-
  API to GSS-SPNEGO as the default channel encryption algorithm.

  adcli uses the GSS-SPNEGO implementation from libsasl2-modules-gssapi-
  mit, a part of cyrus-sasl2. The implementation seems to have some
  compatibility issues with particular configurations of Active
  Directory on recent Windows Server systems.

  Particularly, adcli sends a ldap query to the domain controller, which
  responds with a tcp ack, but never returns a ldap response. The
  connection just hangs at this point and no more traffic is sent.

  You can see it on the packet trace below:

  https://paste.ubuntu.com/p/WRnnRMGBPm/

  On Focal, where the implementation of GSS-SPNEGO is working, we see a
  full exchange, and adcli works as expected:

  https://paste.ubuntu.com/p/8668pJrr2m/

  The fix is to not assume use of confidentiality and integrity modes,
  and instead use the flags negotiated by GSS-API during the initial
  handshake, as required by Microsoft's implementation.

  [Testcase]

  You will need to set up a Windows Server 2019 system, install and
  configure Active Directory and enable LDAP extensions and configure
  LDAPS and import the AD SSL certificate to the Ubuntu client. Create
  some users in Active Directory.

  On the Ubuntu client, set up /etc/hosts with the hostname of the
  Windows Server machine, if your system isn't configured for AD DNS.

  From there, install adcli 0.8.2-1 from -release.

  $ sudo apt install adcli

  Set up a packet trace with tcpdump:

  $ sudo tcpdump -i any port '(389 or 3268 or 636 or 3269)'

  Next, join the AD realm using the normal GSS-API:

  # adcli join --verbose -U Administrator --domain WIN-
  SB6JAS7PH22.testing.local --domain-controller WIN-
  SB6JAS7PH22.testing.local --domain-realm TESTING.LOCAL

  You will be prompted for Administrator's passowrd.

  The output should look like the below:

  https://paste.ubuntu.com/p/NWHGQn746D/

  Next, enable -proposed, and install adcli 0.8.2-1ubuntu1 which caused the regression.
  Repeat the above steps. Now you should see the connection hang.

  https://paste.ubuntu.com/p/WRnnRMGBPm/

  Finally, install the fixed cyrus-sasl2 package, which is available from the
  below ppa:

  https://launchpad.net/~mruffell/+archive/ubuntu/lp1906627-test

  $ sudo add-apt-repository ppa:mruffell/lp1906627-test
  $ sudo apt-get update
  $ sudo apt install libsasl2-2 libsasl2-modules libsasl2-modules-db libsasl2-modules-gssapi-mit

  Repeat the steps. GSS-SPNEGO should be working as intended, and you
  should get output like below:

  https://paste.ubuntu.com/p/W5cJNGvCsx/

  [Where problems could occur]

  Since we are changing the implementation of GSS-SPNEGO, and cyrus-
  sasl2 is the library which provides it, we can potentially break any
  package which depends on libsasl2-modules-gssapi-mit for GSS-SPNEGO.

  $ apt rdepends libsasl2-modules-gssapi-mit
  libsasl2-modules-gssapi-mit
  Reverse Depends:
   |Suggests: ldap-utils
    Depends: adcli
    Conflicts: libsasl2-modules-gssapi-heimdal
   |Suggests: libsasl2-modules
    Conflicts: libsasl2-modules-gssapi-heimdal
   |Recommends: sssd-krb5-common
   |Suggests: slapd
   |Suggests: libsasl2-modules
   |Suggests: ldap-utils
   |Depends: msktutil
    Conflicts: libsasl2-modules-gssapi-heimdal
   |Depends: libapache2-mod-webauthldap
    Depends: freeipa-server
    Depends: freeipa-client
    Depends: adcli
    Depends: 389-ds-base
   |Recommends: sssd-krb5-common
   |Suggests: slapd
   |Suggests: libsasl2-modules
   
  While this SRU makes cyrus-sasl2 work with Microsoft implementations of GSS-SPNEGO, which will be the more common usecase, it may change the behaviour  when connecting to a MIT krb5 server with the GSS-SPNEGO protocol, as krb5 assumes use of confidentiality and integrity modes. This shouldn't be a problem as the krb5 implementation signals its intentions by setting the correct flags during handshake, which these patches to cyrus-sasl2 should now parse correctly.

  [Other Info]

  The below two commits are needed. The first fixes the problem, the second fixes
  some unused parameter warnings.

  commit 816e529043de08f3f9dcc4097380de39478b0b16
  Author: Simo Sorce <simo at redhat.com>
  Date:   Thu Feb 16 15:25:56 2017 -0500
  Subject: Fix GSS-SPNEGO mechanism's incompatible behavior
  https://github.com/cyrusimap/cyrus-sasl/commit/816e529043de08f3f9dcc4097380de39478b0b16

  commit ed2ad48f242fe16e846a9db552a04fca1a5da45f
  Author: Simo Sorce <simo at redhat.com>
  Date:   Tue Apr 11 18:31:46 2017 -0400
  Subject: Drop unused parameter from gssapi_spnego_ssf()
  https://github.com/cyrusimap/cyrus-sasl/commit/ed2ad48f242fe16e846a9db552a04fca1a5da45f

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