linux-kernel - Re: + core_pattern-set-core-helpers-root-and-namespace-to-crashing-process .patch added to -mm tree

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Date:	Tue, 18 Dec 2012 21:06:04 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Neil Horman <nhorman@...driver.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Daniel Berrange <berrange@...hat.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: +
	core_pattern-set-core-helpers-root-and-namespace-to-crashing-process
	.patch added to -mm tree

On 12/17, Neil Horman wrote:
>
> On Mon, Dec 17, 2012 at 05:04:08PM +0100, Oleg Nesterov wrote:
> >
> > > Is there a way to switch all namespaces, except for the pid
> > > namespace?
> >
> > Which exactly namespaces you want to change?
> >
> Ideally, I want the pipe reader process to execute in the same namespaces that
> the crashing process executed in (i.e. the pipe reader should execute as though
> the crashing process forked it).

Yes, and we probably want to change pid_ns as well. But afaics currently
this is not possible, even setns can't do this.

I am starting to think that in this case, perhaps, do_coredump() should
not use call_usermode_helper() at all. Perhaps we can do clone(CLONE_VM) +
commit_creds/restore_root/etc + kernel_execve.

> > To be honest, I do not understand this patch at all. It seems that
> > you need to do something like sys_setns(). But if we do this, then
> > why we can't make core_pattern per-namespace?
> >
> That actually would make sense, although we can't really use setns directly, as
> I don't think we want to open file descriptors to do this manipulation in the
> kernel.

Yes, yes, sure. But this is solveable. We do not really need to open
the files in /proc, we could use proc_ns_operations->install() directly.
Although this is not pretty.

> Perhaps its best just to restrict this patch to adjusting the root fs location
> for the chroot case.

Probably... at least for the start.

BTW. Of course this is subjective, but personally I think that "||"
looks strange. Perhaps it would be better to add something like
--croot argument?

Oleg.

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