[refpolicy] init_upstart and the init_t->sysadm_t transition

Stephen Smalley sds at tycho.nsa.gov
Tue Feb 23 12:42:09 CST 2010


Hi,

The refpolicy (and the example policy before it) has always defined a
domain transition from init_t to sysadm_t on shell_exec_t in order to
automatically transition to sysadm_t for single-user mode.  When
distributions moved to upstart, this has to be made conditional on
init_upstart == false since upstart runs scripts via shell commands,
with a transition to initrc_t defined in the case where init_upstart ==
true.  In OpenSUSE, we have now seen a case where we have a
sysvinit-based system that also seems to be running the scripts via
shell commands.  Although the precise reason is still unclear to me, in
looking at the sysvinit code, I have found that this is a possible code
path for sysvinit - it will invoke the command string via $SHELL -c if
the command string in /etc/inittab has any meta characters or if the
initial attempt to exec the command fails with ENOEXEC (e.g. script that
lacks #! header).

This suggests that the automatic transition to sysadm_t isn't reliable
even with sysvinit and perhaps we should have just always used an
explicit mechanism (sulogin or one could set up a script wrapper for
establishing single-user mode with suitable transitions defined).
Fedora is trying to resolve how to get single-user mode into an
appropriate context, although I haven't seen a final resolution yet:
http://lists.fedoraproject.org/pipermail/devel/2010-January/129566.html
(original proposal was to use sulogin by default, but there was some
opposition to that)

I'm wondering whether we should just drop sysadm_shell_domtrans(init_t)
altogether.  Or if we retain it, reverse the default case (and ideally
rename the boolean to reflect the fact that it isn't dependent on use of
upstart, although that may be difficult to do cleanly/compatibly).

-- 
Stephen Smalley
National Security Agency



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