Comment 29 for bug 423252

We use LDAP over TLS via PAM for auth, and use NSSWITCH as well. After upgrade from Hardy -> Jaunty -> Karmic, su no longer functioned, however sudo did work.

Here is what I found. When upgrading to Karmic, keeping our old /etc/pam.d/common-auth failed for su. Putting in the default common-auth from a fresh install of Karmic works.

Old /etc/pam.d/common-auth:
auth sufficient pam_ldap.so debug
auth sufficient pam_unix.so try_first_pass likeauth nullok
auth required pam_deny.so
auth required pam_nologin.so

Baseline Karmic /etc/pam.d/common-auth that works (snippet):
# here are the per-package modules (the "Primary" block)
auth [success=2 default=ignore] pam_unix.so nullok_secure
auth [success=1 default=ignore] pam_ldap.so use_first_pass
# here's the fallback if no module succeeds
auth requisite pam_deny.so
# prime the stack with a positive return value if there isn't one already;
# this avoids us returning an error just because nothing sets a success code
# since the modules above will each just jump around
auth required pam_permit.so

Our relavent nsswitch lines:
passwd: files ldap
group: files ldap
shadow: files ldap

Relevant /etc/ldap.conf lines:
ssl start_tls
tls_checkpeer no

So, after "fixing" the common-auth file, su began working for us. Hope that is helpful.