When using Syncrepl…

rthomson — Wed, 01 Sep 2010 01:23:35 +0000

Quick OpenLDAP tip boys & girls…

When using syncrepl to replicate from a master LDAP server to a slave LDAP server, always remember to configure the ACLs on the master LDAP server to allow the “sync dn” to read everything.

I know it sounds entirely obvious but today I realized that the order in which I had defined the ACLs on the master LDAP server was preventing the sync dn from reading the “userPassword” attribute and thus also preventing it from syncing it to the slave. The consequence of which was that users would not be able to authenticate against the slave server! Shit!

Of course, since everything else was syncing properly, all the NSS (lookup) stuff worked fine but anything authentication related like PAM wouldn’t work because the user bind would fail with “Invalid credentials” in /var/log/secure. It had a been some time since I tested authentication so I must never have actually tested authentication against the slave (whoops!) and thus didn’t notice until now. I know I tested lookups but testing authentication must have slipped by somehow. Grrr, testing.

Good thing I caught the problem early and it never escalated into a problem, that really could have sucked down the line.

Don’t make the same mistake I did.

POSIX Default ACLs, umask and Project Directories

rthomson — Fri, 23 Apr 2010 22:32:42 +0000

I’ve recently come across a situation where the inherent design of POSIX ACLs has left me scratching my head for a solution to the problem of setting up a “project” or “group share” directory on Linux. The problem is as follows: We have several different projects or groups that desire a directory where any and every file created, copied or moved to said directory will become owned by a particular group and have group read/write permissions set automatically.

Most of the problem is solved through age-old UNIX techniques. For group ownership, all we need to do is setup the top-level directory to be owned by the “project” or “group share” group and setgid the directory:

$ mkdir project1
$ chown .projgroup project1
$ chmod g+s project1

This effectively forces every file created, moved or copied into the “project1″ directory to be owned by group “projgroup”. So far, so good. The difficulties begin when we attempt to use default ACLs to enforce the permissions of any files created, moved or copied into the directory.

The POSIX ACL standard defines “default” ACLs which can be applied to a directory, which are in turn inherited by newly created/copied/moved child files and directories. While the default ACLs are inherited properly, the ACL mask when applied to files copied into the group share directory WITHOUT previous group write set prevents the files from being group writable!

$ getfacl project1
# file: project1
# owner: root
# group: projgroup
user::rwx
group::rwx
other::r--
default:user::rw-
default:group::rw-
default:group:projgroup:rw-
default:mask::rwx
default:other::r--

So far so good, right?

$ ls -alh test
-rw-r--r--  1 user1 user 0 Apr 23 15:10 test
$ cp test project1
$ ls -alh project1/test
-rw-r--r--+ 1 user1 projgroup 0 Apr 23 15:10 project1/test

What the… ?!?! No group write? Noooooo!

$ getfacl project1
# file: project1/test
# owner: user1
# group: projgroup
user::rw-
group::rw-			#effective:r--
group:projgroup:rw-		#effective:r--
mask::r--
other::r--

And so we have the great POSIX ACL mask problem, which is by design in fact. Still looking for a complete solution that doesn’t involve global trying to force a specific umask on every account… It would be nice if I could ensure that every file had group write set before it was copied into the group share directory but alas, I cannot. Telling users to manually check and change permissions is also a pain. Cron jobs to change group write recursively is also ugly. Please, someone provide me with the solution.

techslaves.org » acl

When using Syncrepl…

POSIX Default ACLs, umask and Project Directories