Description of problem:


  If you setup postgresql to use pam authentication, it will fail to authenticate for pam_unix (local account) logins.  It will work for pam_krb5 logins.

  By reading the unix_chkpwd man page, I learned that it can also expect to be sgid in the shadow group.  By adding a shadow group, making /usr/sbin/unix_chkpwd and /etc/shadow owned by root:shadow, and making /usr/sbin/unix_chkpwd suid root and sgid shadow, and finally making /etc/shadow 040 for permissions, I was able to get it to work.  Unfortunately, when the new pam update came down, it blew away the file permissions and changed the ownership back on /usr/sbin/unix_chkpwd.  It started working again, once I changed it back to how I described it.


Version-Release number of selected component (if applicable):


I believe this effects multiple versions, but I haven't checked them all.  

The one I tested on RHEL 7.2 and 7.3 was pam-1.1.8-18 and whatever one comes as the default for RHEL 7.2 with it not yet updated.





How reproducible:

Very reproducible and deterministic.




Steps to Reproduce:



I first figured it out on a 7.3 system.  I took a RHEL 7.2 ISO and installed it into a VM clean, installed postgresql-server and setup a database with a user to match a local user account name.  Next, I changed all of the methods to pam in pg_hba.conf, and restarted postgresql.  I then attempted to connect to localhost using a local user account  (testuser), and got the messages

unix_chkpwd[21460]: check pass; user unknown
unix_chkpwd[21461]: check pass; user unknown
unix_chkpwd[21461]: password check failed for user (testuser)
journal: nweb testxdb 129.237.45.177(37182) authentication: pam_unix(postgresql:auth): authentication failure; logname= uid=26 euid=26 tty= ruser= rhost=127.0.0.1  user=testuser

After making the changes I described above, I tried again, and was able to get authenticated.


(Some of this is from memory, so please forgive if I added an unneeded step as I'm walking through shell history.)

As root:
0. adduser testuser and give it a password.
1. yum install postgresql postgresql-contrib postgresql-server
2. su - postgres
3. initdb
4. exit
5. systemctl start postgresql.service
6. su - postgres
7. createuser testuser
8. modify pg_hba.conf to have all methods changed from trust to pam.
8.?   you may need to modify  postgresql.conf's listen_addresses to be '*'.
9. exit
10. systemctl stop postgresql.service
11. systemctl start postgresql.service
12. su - testuser
13. psql postgres  
14. Enter the password.  When it fails, check the results in /var/log/secure
15. exit # Back to root

The FIX (as root):
16. groupadd shadow
17. chown root:shadow /etc/shadow /usr/sbin/unix_chkpwd
18. chmod 6755 /usr/sbin/unix_chkpwd
19. chmod 0040 /etc/shadow
20. su - testuser
21. psql postgres
22. Enter the password, and you are in.


Actual results:

Unable to login to database.  PAM Authentication fails for correct password.  (I even changed the password to something horribly simple, and retried multiple times to make sure I wasn't typing my long password incorrectly.)

Expected results:

User should be able to login and have it authenticate against the local account.


Additional info:

I saw one place mention this on the web for centos 6 also.  I did see some other pam_unix issues in bugzilla for other services, which may be having similar problems.  I choose to document this for the use case I was having, since I can't be sure without testing it and knowing something about those services.