linux-kernel - Re: [patch 05/10] add "permit user mounts in new namespace" clone flag

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Date:	Thu, 12 Apr 2007 22:45:33 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	"Serge E. Hallyn" <serue@...ibm.com>
Cc:	Miklos Szeredi <miklos@...redi.hu>, containers@...ts.osdl.org,
	viro@....linux.org.uk, linux-fsdevel@...r.kernel.org,
	akpm@...ux-foundation.org, linuxram@...ibm.com,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 05/10] add "permit user mounts in new namespace" clone flag

"Serge E. Hallyn" <serue@...ibm.com> writes:

> Quoting Miklos Szeredi (miklos@...redi.hu):
>> From: Miklos Szeredi <mszeredi@...e.cz>
>> 
>> If CLONE_NEWNS and CLONE_NEWNS_USERMNT are given to clone(2) or
>> unshare(2), then allow user mounts within the new namespace.
>> 
>> This is not flexible enough, because user mounts can't be enabled for
>> the initial namespace.
>> 
>> The remaining clone bits also getting dangerously few...
>> 
>> Alternatives are:
>> 
>>   - prctl() flag
>>   - setting through the containers filesystem
>
> Sorry, I know I had mentioned it, but this is definately my least
> favorite approach.
>
> Curious whether are any other suggestions/opinions from the containers
> list?

Given the existence of shared subtrees allowing/denying this at the mount
namespace level is silly and wrong.

If we need more than just the filesystem permission checks can we
make it a mount flag settable with mount and remount that allows
non-privileged users the ability to create mount points under it
in directories they have full read/write access to.

I don't like the use of clone flags for this purpose but in this
case the shared subtress are a much more fundamental reasons for not
doing this at the namespace level.

Eric
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