[refpolicy] chsh (chfn_t) to access /etc/.pwd.lock (shadow_t) ?

Sven Vermeulen sven.vermeulen at siphos.be
Tue Mar 27 14:24:47 CDT 2012


In Gentoo, we notice that recent shadow package (version 4.1.5) has a change
in behavior for changing account information through chsh. Although the
application only edits /etc/passwd entries, it now uses the /etc/.pwd.lock
file to prevent concurrent changes to the /etc/passwd (and other
account-related files). 

In the current policy however, /etc/.pwd.lock is marked as shadow_t, so the
chsh application (running in chfn_t) does not have the proper privileges to
work on this. As a result, it fails to update /etc/passwd entries.

As I'm not going to give it read/write access to shadow_t files, one other
possibility would be to mark /etc/.pwd.lock as etc_t. But I can imagine that
it was given shadow_t on purpose previously, probably to prevent a malicious
program (that has write access to etc_t) to update the lock file so
concurrent write operations on /etc/shadow could result in corruption...

Another solution would be to patch chsh itself to use a different lock file,
but unless it's accepted upstream, it's only a "local" remedy.

A third solution would be to create and use a different type for it, like
etc_auth_lock_t or whatever imagination can bring to life, and update the
policies of all domains that need access to it towards it.

Any thoughts on this?

Wkr,
	Sven Vermeulen



More information about the refpolicy mailing list