linux-ext4 - Re: [PATCH RFC v2 2/6] fs: protected project id

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Message-ID: <CALCETrUb8JG6P2==M5d=XnhE-6Z04neo+_h3dtTP-ZyCmAkMnQ@mail.gmail.com>
Date:	Tue, 10 Mar 2015 11:57:01 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Konstantin Khlebnikov <koct9i@...il.com>
Cc:	Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>,
	Dave Chinner <david@...morbit.com>, Jan Kara <jack@...e.cz>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	"Theodore Ts'o" <tytso@....edu>,
	Dmitry Monakhov <dmonakhov@...nvz.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Li Xi <pkuelelixi@...il.com>
Subject: Re: [PATCH RFC v2 2/6] fs: protected project id

On Tue, Mar 10, 2015 at 11:51 AM, Konstantin Khlebnikov
<koct9i@...il.com> wrote:
> On Tue, Mar 10, 2015 at 8:32 PM, Andy Lutomirski <luto@...capital.net> wrote:
>> On Tue, Mar 10, 2015 at 10:22 AM, Konstantin Khlebnikov
>> <khlebnikov@...dex-team.ru> wrote:
>>> Historically XFS project id doesn't have any permission control: file owner
>>> is able to set any project id. Later they was sealed with user-namespace:
>>> XFS allows to change it only from init user-ns. That works fine for isolated
>>> containers or if user doesn't have direct access to the filesystem (NFS/FTP).
>>>
>>> This patch adds sysctl fs.protected_projects which makes changing project id
>>> privileged operation which requires CAP_SYS_RESOURCE in current user-namespace.
>>> Thus there are two levels of protection: project id mapping in user-ns defines
>>> set of permitted projects and capability protects operations within this set.
>>
>> If I understand this right, this doesn't work.  If I lack
>> CAP_SYS_RESOURCE but I have two projids mapped, then I can create a
>> new userns, map both projids, and get CAP_SYS_RESOURCE.
>
> Setting project id mapping for nested user-namespace also requires
> this capability in parent namespace. The same as for setting uid/gid
> mapping but without special case for mapping current uid/gid because
> task has no "current" project id.
>
> This is mentioned in cover letter but I forget it here. Sorry.

Right, sorry.  I'm still used to projid mappings being unprotected.

--Andy

>
>>
>> --Andy
>> --
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-- 
Andy Lutomirski
AMA Capital Management, LLC
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