Q: selinux_bprm_committed_creds() && signals/do_wait

From: Oleg Nesterov <oleg@redhat.com>
To: David Howells <dhowells@redhat.com>,
	Eric Paris <eparis@parisplace.org>,
	James Morris <jmorris@namei.org>,
	Roland McGrath <roland@redhat.com>,
	Stephen Smalley <sds@tycho.nsa.gov>
Cc: linux-kernel@vger.kernel.org
Subject: Q: selinux_bprm_committed_creds() && signals/do_wait
Date: Wed, 29 Apr 2009 00:30:25 +0200	[thread overview]
Message-ID: <20090428223025.GA11997@redhat.com> (raw)

selinux_bprm_committed_creds:

	rc = avc_has_perm()
	if (rc) {
		flush_signals(current);

This doesn't look right. If the task was SIGKILL'ed we must not proceed,
the task should die. The fix is simple, we should check SIGNAL_GROUP_EXIT
and do nothing in this case, the task will exit before return to user
space. If SIGNAL_GROUP_EXIT is set, it is just wrong to drop SIGKILL and
continue.

But, before fixing, I'd like to understand why we are doing

		flush_signal_handlers(current, 1);
		sigemptyset(&current->blocked);

later. Could someone explain ? This looks unneeded.

Another question,

	wake_up_interruptible(&current->parent->signal->wait_chldexit);

Shouldn't we use ->real_parent ? Afaics, we shouldn't worry about the tracer
if current is ptraced, exec must not succeed if the tracer has no rights to
trace this task after cred changing. But we should notify ->real_parent which
is, well, real parent.

Also, we don't need _irq to take tasklist_lock, and we don't actually need
->siglock.

Oleg.