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Message-ID: <m1d51x2z16.fsf@ebiederm.dsl.xmission.com>
Date: Sat, 21 Apr 2007 15:33:25 -0600
From: ebiederm@...ssion.com (Eric W. Biederman)
To: Andi Kleen <andi@...stfloor.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Miklos Szeredi <miklos@...redi.hu>, serue@...ibm.com,
viro@....linux.org.uk, linuxram@...ibm.com,
linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
containers@...ts.osdl.org
Subject: Re: [patch 7/8] allow unprivileged mounts
Andi Kleen <andi@...stfloor.org> writes:
> Andrew Morton <akpm@...ux-foundation.org> writes:
>
>> On Fri, 20 Apr 2007 12:25:39 +0200 Miklos Szeredi <miklos@...redi.hu> wrote:
>>
>> > Define a new fs flag FS_SAFE, which denotes, that unprivileged
>> > mounting of this filesystem may not constitute a security problem.
>> >
>> > Since most filesystems haven't been designed with unprivileged
>> > mounting in mind, a thorough audit is needed before setting this flag.
>>
>> Practically speaking, is there any realistic likelihood that any filesystem
>> apart from FUSE will ever use this?
>
> If it worked for mount --bind for any fs I could see uses of this. I haven't
> thought
> through the security implications though, so it might not work.
Binding a directory that you have access to in other was is essentially
the same thing as a symlink. So there are no real security implications
there. The only problem case I can think of is removal media that you
want to remove but someone has made a bind mount to. But that is
essentially the same case as opening a file so there are no new
real issues. Although our diagnostic tools will likely fall behind
for a bit.
We handle the security implications by assigning an owner to all mounts
and only allowing you to add additional mounts on top of a mount you
already own.
If you have the right capabilities you can create a mount owned by
another user.
For a new mount if you don't have the appropriate capabilities nodev
and nosuid will be forced.
Initial super block creation is a lot more delicate so we need the
FS_SAFE flag, to know that the kernel is prepared to deal with the
crazy things that a hostile user space is prepared to do.
Eric
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