linux-kernel - Re: Q: selinux_bprm_committed_creds() && signals/do

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Message-ID: <alpine.LRH.2.00.0904291024001.5246@tundra.namei.org>
Date:	Wed, 29 Apr 2009 10:29:06 +1000 (EST)
From:	James Morris <jmorris@...ei.org>
To:	Oleg Nesterov <oleg@...hat.com>
cc:	David Howells <dhowells@...hat.com>,
	Eric Paris <eparis@...isplace.org>,
	Roland McGrath <roland@...hat.com>,
	Stephen Smalley <sds@...ho.nsa.gov>,
	linux-kernel@...r.kernel.org
Subject: Re: Q: selinux_bprm_committed_creds() && signals/do_wait

On Wed, 29 Apr 2009, Oleg Nesterov wrote:

> 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.

I'm not quite sure what you're asking.  This is a permission check to see 
if the new task can inherit the signal state of the parent, and if not, 
the new task's signal state is flushed.

Where does a consideration of SIGKILL arise?

> 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.

This is part of clearing all the signal state in the child.

> 
> 
> 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.
> 

-- 
James Morris
<jmorris@...ei.org>
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