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

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Message-ID: <20090429102511.GA10767@redhat.com>
Date:	Wed, 29 Apr 2009 12:25:11 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	David Howells <dhowells@...hat.com>
Cc:	James Morris <jmorris@...ei.org>,
	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 04/29, David Howells wrote:
>
> Oleg Nesterov <oleg@...hat.com> wrote:
>
> > we can flush the signal which was sent after we changed SID/cred and passed
> > the new permission checks,
>
> I think you mean to say, rather, that we can *lose* a signal that was sent,
> because flush_signals() discards all pending signals unconditionally, and so
> SIGKILL can be lost?

Yes, thanks.

> I suspect we should pass SIGKILL

Or we can fliter out SIGKILLs, yes.

But this doesn't differ from "do nothing if SIGNAL_GROUP_EXIT", except needs
a bit more changes. If SIGNAL_GROUP_EXIT is true, we must have a pending
SIGKILL. Either way the task never returns to user-space.

> and possibly SIGSTOP through the flush.

Yes, perhaps... But I don't know if this is right from the selinux pov.
Perhaps it was queued before we changed SID.

And. It is possible that the task/user who sent SIGSTOP before changing
SID will not able to send SIGCONT later.

Oleg.

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