From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760544Ab3HOH4s (ORCPT ); Thu, 15 Aug 2013 03:56:48 -0400 Received: from out02.mta.xmission.com ([166.70.13.232]:39557 "EHLO out02.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760494Ab3HOH4o (ORCPT ); Thu, 15 Aug 2013 03:56:44 -0400 From: ebiederm@xmission.com (Eric W. Biederman) To: Andy Lutomirski Cc: Miklos Szeredi , "Serge E. Hallyn" , Al Viro , Linux-Fsdevel , Kernel Mailing List References: <87a9kkax0j.fsf@xmission.com> <8761v7h2pt.fsf@tw-ebiederman.twitter.com> Date: Thu, 15 Aug 2013 00:55:25 -0700 In-Reply-To: (Andy Lutomirski's message of "Wed, 14 Aug 2013 23:52:11 -0700") Message-ID: <87bo4zfkwi.fsf@tw-ebiederman.twitter.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-AID: U2FsdGVkX18ZF8uWLov+GCbMQJLjoRYAmrURxpMqCl0= X-SA-Exim-Connect-IP: 98.207.154.105 X-SA-Exim-Mail-From: ebiederm@xmission.com X-Spam-Report: * -1.0 ALL_TRUSTED Passed through trusted hosts only via SMTP * 0.0 T_TM2_M_HEADER_IN_MSG BODY: T_TM2_M_HEADER_IN_MSG * -3.0 BAYES_00 BODY: Bayes spam probability is 0 to 1% * [score: 0.0007] * -0.0 DCC_CHECK_NEGATIVE Not listed in DCC * [sa06 1397; Body=1 Fuz1=1 Fuz2=1] X-Spam-DCC: XMission; sa06 1397; Body=1 Fuz1=1 Fuz2=1 X-Spam-Combo: ;Andy Lutomirski X-Spam-Relay-Country: Subject: Re: DoS with unprivileged mounts X-Spam-Flag: No X-SA-Exim-Version: 4.2.1 (built Wed, 14 Nov 2012 14:26:46 -0700) X-SA-Exim-Scanned: Yes (on in01.mta.xmission.com) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Andy Lutomirski writes: > On Wed, Aug 14, 2013 at 11:45 PM, Eric W. Biederman > wrote: >> Miklos Szeredi writes: >> >> Part of me does prefer the semantics Andy has suggested where instead of >> unmounting things we have something like a skeleton of the mount tree >> unioned with dcaches of the filesystems themselves. With "struct >> mountpoint" we are amazing close to that already. > > Two possible nasty cases: > > 1. mount whatever /tmp/foo/bar; rmdir /tmp/foo/bar; rmdir /tmp/foo > > Presumably ls /tmp shouldn't show foo. Should cd /tmp/foo/bar work? > What about umount /tmp/foo/bar? What about cd /tmp/foo? You have to have two mount namespaces or at least two different paths to to the same filesystem to make this work. rdir /tmp/foo/bar where /tmp/foo/bar is a mountpoint in your mount namespace will not work because you are trying to remove a root directory. So the semantics I would expect to see if it was implementable is /tmp/foo and /tmp/foo/bar would continue to exist on the paths where /tmp/foo/bar was a mount point and would disappear as soon as it was unmounted. > 2. mount whatever /tmp/foo; rmdir /tmp/foo; mkdir /tmp/foo > > Ugh. Likewise. I would expect to see the new /tmp/foo slide under the old /tmp/foo mountpoint. Essentially my expectation would be that the mount points would float over the filesystems. Semantically I like it, and have played with the idea before. Implementation wise shrug I didn't realize any of this was close to being practically implementatable until today. Eric