From: ebiederm@xmission.com (Eric W. Biederman)
To: Andrew Vagin <avagin@parallels.com>
Cc: Al Viro <viro@ZenIV.linux.org.uk>,
Andrey Vagin <avagin@openvz.org>, <linux-fsdevel@vger.kernel.org>,
<linux-kernel@vger.kernel.org>,
Serge Hallyn <serge.hallyn@canonical.com>
Subject: Re: [PATCH] umount: Do not allow unmounting rootfs.
Date: Tue, 07 Oct 2014 13:58:01 -0700 [thread overview]
Message-ID: <87iojvvbqe.fsf@x220.int.ebiederm.org> (raw)
In-Reply-To: <20141007195307.GA23694@paralelels.com> (Andrew Vagin's message of "Tue, 7 Oct 2014 23:53:07 +0400")
Andrew Vagin <avagin@parallels.com> writes:
> On Tue, Oct 07, 2014 at 12:27:06PM -0700, Eric W. Biederman wrote:
>>
>> Which in practice is totally uninteresting. Only the global root user can
>> do it, and it is just a stupid thing to do.
>>
>> However that is no excuse to allow a silly way to oops the kernel.
>>
>> We can avoid this silly problem by setting MNT_LOCKED on the rootfs
>> mount point and thus avoid needing any special cases in the unmount
>> code.
>
> I had this idea too, but it doesn't work.
>
> MNT_LOCKED isn't inherited, if the privileged user creates a new mount
> namespace.
>
> So "unshame -m ./nsenter" reproduces the same BUG.
Which broken tree do you have where MNT_LOCKED is not inherited?
That case fails to reproduce the BUG for me.
The semantics of MNT_LOCKED are that you aren't allowed to see what is
beneath. So if you can get under there even by unsharing the mount
namespace it is an implementation bug in MNT_LOCKED.
Eric
next prev parent reply other threads:[~2014-10-07 20:58 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-07 12:00 [PATCH] mnt: don't allow to detach the namespace root Andrey Vagin
2014-10-07 13:24 ` Al Viro
2014-10-07 13:40 ` Andrew Vagin
2014-10-07 19:27 ` [PATCH] umount: Do not allow unmounting rootfs Eric W. Biederman
2014-10-07 19:53 ` Andrew Vagin
2014-10-07 20:58 ` Eric W. Biederman [this message]
2014-10-07 22:00 ` Andrew Vagin
2014-10-07 23:35 ` Eric W. Biederman
2014-10-07 23:40 ` [PATCH] mnt: Move the clear of MNT_LOCKED from copy_tree to it's Eric W. Biederman
2014-10-08 10:46 ` Andrew Vagin
2014-10-08 10:47 ` [PATCH] umount: Do not allow unmounting rootfs Andrew Vagin
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