From mboxrd@z Thu Jan 1 00:00:00 1970 From: ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org (Eric W. Biederman) Subject: Re: [PATCH] userns: allow privileged user to operate locked mount Date: Thu, 14 Nov 2013 17:38:48 -0800 Message-ID: <871u2i30lz.fsf@xmission.com> References: <1384327663-12032-1-git-send-email-gaofeng@cn.fujitsu.com> <874n7e4k78.fsf@xmission.com> <52856F0D.8090206@cn.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <52856F0D.8090206-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org> (Gao feng's message of "Fri, 15 Nov 2013 08:47:09 +0800") List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Gao feng Cc: linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: containers.vger.kernel.org Gao feng writes: > On 11/15/2013 07:50 AM, Eric W. Biederman wrote: >> Gao feng writes: >> >>> Privileged user should have rights to mount/umount/move >>> these even locked mount. >> >> Hmm. This is pretty much a can't happen case, as the only exist in mount >> namespaces where the global root isn't the root. How are you getting >> into this situation? Using setns() ? >> > > Before, priviged user can use setns to set his mount namespace to the > container's mount namespace, and change container's mount directly. > this patch just gives back host the control of container. Having thought about this patch a little more I really don't like it. There are other ways for a privileged user to get around the limitations when the mount namespace is being created or the mounts are being propagated. This approach would require more then a signgle bit of accounting to work in the nested user namespace case. The lock says one or several mounts are mounted as a unit and need to stay that way. If there are real advantages to splitting things up I might be persuaded to change my mind. But right now it looks like you are introducing extra complexity for a very corner edge case that we don't want to encourage people to use. Eric