linux-kernel - Re: [RFC][PATCH 3/5] Determine if sender is from ancestor ns

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Message-ID: <20081202114833.GA1132@wavehammer.waldi.eu.org>
Date:	Tue, 2 Dec 2008 12:48:33 +0100
From:	Bastian Blank <bastian@...di.eu.org>
To:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
Cc:	oleg@...hat.com, ebiederm@...ssion.com, roland@...hat.com,
	containers@...ts.osdl.org, linux-kernel@...r.kernel.org,
	xemul@...nvz.org
Subject: Re: [RFC][PATCH 3/5] Determine if sender is from ancestor ns

On Mon, Dec 01, 2008 at 12:15:06PM -0800, Sukadev Bhattiprolu wrote:
> Bastian Blank [bastian@...di.eu.org] wrote:
> | If I see this correctly this information is already covered in si_code
> | with SI_USER and SI_TKILL. SI_KERNEL is used for explicit kernel
> | generated signals.
> 
> Yes, but si_code from sys_rt_sigqueueinfo() cannot be trusted.

sys_rt_sigqueueinfo disallows setting si_code to any value which
describes kernel signals from userspace. So using SI_FROMUSER should be
sufficient.

> IOW, we need to find the namespace of the sender only if the sender is
> a user process. If signal is originating from kernel, safely checking
> namespace becomes more complex.

Where does this imply checking sender for kernel generated signals?

> Yes, current approach is somewhat hacky. We tried other approaches
> before and they were either intrusive or required non-trivial changes
> to semantics of signals to global init or both.

Message-IDs?

> | > +static inline int siginfo_from_ancestor_ns(struct task_struct *t,
> | > +			siginfo_t *info)
> | > +{
> | > +	if (!is_si_special(info) && (info->si_signo & SIG_FROM_USER)) {
> | > +		/* if t can't see us we are from parent ns */
> | What?
> I assume your question is about the comment :-)

Yes.

> Yes, a process can see all its descendants and processes in descendant
> namespaces. But it can only see its ancestors upto the most recent
> CLONE_NEWPID. (kind of like chroot in filesystems). So if receiver
> can't see sender, sender must be an ancestor.

Please add a complete comment to the function which describes the
function. And don't us "it" for not defined entities.

Bastian

-- 
I have never understood the female capacity to avoid a direct answer to
any question.
		-- Spock, "This Side of Paradise", stardate 3417.3
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