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

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Message-ID: <CALYGNiP0u51JVtAROdNpK5hYKHrtpT1WSyKS_tqxsTKZ7FWKvw@mail.gmail.com>
Date:	Tue, 10 Mar 2015 21:51:59 +0300
From:	Konstantin Khlebnikov <koct9i@...il.com>
To:	Andy Lutomirski <luto@...capital.net>
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 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.

>
> --Andy
> --
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