Re: crash: cyrus-imapd -> sasl -> pam -> pam_ldap -> libldap-2.x -> sasl

["Kurt D. Zeilenga" <Kurt@OpenLDAP.org>]

That seems like a lot of work just to get plain authentication.
Besides the quick (rm sasl_set_alloc call) hack you and others
have suggested, I would suggest moving SASL's PAM code into
pwcheckd.  This would isolate the SASL caller from the SASL
password check mechanism.

At 11:09 AM 11/28/00 +0100, Julio Sanchez Fernandez wrote:

>A problem has been detected when using both Cyrus 2.x and OpenLDAP 2.x
>together if pwcheck_method is PAM and pam_ldap is used.
>
>It does not fail for everyone.  For instance, on RedHat 7.0 using
>system-auth as configured by authconf, pam_unix is used before
>pam_ldap and the crash is not seen.
>
>However, if pam_pwdb is used instead, crash happens.  It also happens
>if pam_ldap is tried before pam_unix *unless* authentication fails:
>that is, you try the wrong password and then you retry (in the same
>connection, of course) the right one and does not crash.  Or does not
>crash for a few of us.  The thing is fragile enough, so it may work by
>dumb luck at any time.
>
>The problem has been traced to the call to sasl_set_alloc in cyrus.c
>in libldap, that is used to set the memory management routines used by
>cyrus-sasl to those in liblber.  But in the scenario described in the
>subject, the sasl library is what called libldap (indirectly through
>PAM).  And now, libldap will call libsasl and change the memory
>routines.
>
>Apparently, the crash happens when pam returns to cyrus-sasl and it
>tries to clean up, by calling the memfree routines in liblber and,
>somehow (possibly pam unloads the libraries), they are not there
>anymore.  The reason why pam_unix avoids the crash may be that it just
>does getpwnam or getspnam that triggers loading libldap through
>nss_ldap and the latter keeps libldap and liblber mapped until program
>end.  That a failed authentication saves the day may be caused by a
>similar hidden library load.
>
>Removing the call to sasl_set_alloc avoids the crash.
>
>Now, the questions are: Why do we call sasl_set_alloc?  Do we need it?
>Always? On some platforms? Is it safe doing it when we were called by
>libsasl itself? If not, how do we manage memory allocation when we are
>running under libsasl?
>
>Ideas?
>
>Julio