[Bug 1326500] [NEW] libgssapi-krb5-2: segfault when mechglue loops endlessly on call to gss_add_cred_from

[Sam Hartman]

Public bug reported:

There's a bug fixed in krb5 1.12.1+dfsg-2 (just uploaded to Debian) where if a gss-api mechanism is dynamically loaded, and that mechanism uses symbols from libgssapi_krb5, and doesn't provide certain optional entry points added in krb5 1.12, then calling one of those entry points will cause the mechglue to call itself.  This results in an endless loop and the process eventually crashes on stack exhaustion.
Unfortunately, one of the entry points, gss_add_cred_from is going to get called quite commonly.
So, this means that if you're using Ubuntu to develop a GSS-API mechanism or are installing a third party gss-api mechanism, things are going to crash, mostly whenever anyone tries to use gss-api as a server, regardless of whether they intended to use your application.

I'd like to see this fixed in trusty, so I'm giving a detailed repro below.  Patch against trusty coming shortly.
Apologies that the repro is a bit involved; there's not a mechanism packaged in Ubuntu that easily exhibits this.  However, you really ought to be able to use Ubuntu to develop a GSS mechanism without crashing all your gss apps.

On a stock trusty system, first install the attached mech file as
/usr/etc/gss/mech (yes that's /usr/etc, not /etc) and then run the
following:

  sudo add-apt-repository  ppa:moonshot/daily
  sudo apt-get update
    4  sudo apt-get  install bzr libkrb5-dev libradsec-dev   libssl-dev libjansson-dev autoconf automake libtool  build-essential
  bzr branch -r739 lp:moonshot
  cd moonshot/
  autoreconf  -i
  ./configure --without-opensaml --without-shibresolver
  make -j3
  sudo make install
  sudo apt-get install krb5-gss-samples
  gss-server host at localhost

This will segfault

** Affects: krb5 (Ubuntu)
     Importance: Undecided
         Status: Confirmed

** Attachment added: "file to install as /usr/etc/gss/mech"
   https://bugs.launchpad.net/bugs/1326500/+attachment/4125454/+files/mech

** Changed in: krb5 (Ubuntu)
       Status: New => Confirmed

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Title:
  libgssapi-krb5-2: segfault when mechglue loops endlessly on call to
  gss_add_cred_from

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