Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933060Ab3HNTyQ (ORCPT ); Wed, 14 Aug 2013 15:54:16 -0400 Received: from out03.mta.xmission.com ([166.70.13.233]:52302 "EHLO out03.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932813Ab3HNTyP (ORCPT ); Wed, 14 Aug 2013 15:54:15 -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: <520BD9E0.8050304@mit.edu> Date: Wed, 14 Aug 2013 12:53:48 -0700 In-Reply-To: <520BD9E0.8050304@mit.edu> (Andy Lutomirski's message of "Wed, 14 Aug 2013 12:26:24 -0700") Message-ID: <8761v882wj.fsf@xmission.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-AID: U2FsdGVkX1/TCPcQgSAg/VY+cUH0iXShZ809nZUUF60= 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 * -0.0 BAYES_20 BODY: Bayes spam probability is 5 to 20% * [score: 0.0861] * -0.0 DCC_CHECK_NEGATIVE Not listed in DCC * [sa04 1397; Body=1 Fuz1=1 Fuz2=1] X-Spam-DCC: XMission; sa04 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 in02.mta.xmission.com) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1352 Lines: 32 Andy Lutomirski writes: > On 08/14/2013 10:42 AM, Miklos Szeredi wrote: >> There's a simple and effective way to prevent unlink(2) and rename(2) >> from operating on any file or directory by simply mounting something >> on it. In any mount instance in any namespace. >> >> Was this considered in the unprivileged mount design? >> >> The solution is also theoretically simple: mounts in unpriv namespaces >> are marked "volatile" and are dissolved on an unlink type operation. > > I'd actually prefer the reverse: unprivileged mounts don't prevent > unlink and rename. If the dentry goes away, then the mount could still > exist, sans underlying file. (This is already supported on network > filesystems.) Of course we do this in network filesystems by pretending the rename/unlink did not actually happen. The vfs insists that it be lied to instead of mirroring what actually happened. Again all of this is a question about efficient data structures and not really one of semantics. Can either semantic be implemented in such a way that it does not slow down the vfs? Eric -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/