From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andy Lutomirski Subject: Re: CLONE_NEWUSER|CLONE_FS root exploit Date: Wed, 13 Mar 2013 18:48:23 -0700 Message-ID: <51412C67.30908@mit.edu> References: <20130313175729.GH12501@outflux.net> <87r4jjkv18.fsf@xmission.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <87r4jjkv18.fsf-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org> 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: "Eric W. Biederman" Cc: containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, Sebastian Krahmer , Kees Cook , Oleg Nesterov , Linux Kernel Mailing List List-Id: containers.vger.kernel.org On 03/13/2013 11:35 AM, Eric W. Biederman wrote: > Kees Cook writes: > >> Hi, >> >> It seem like we should block (at least) this combination. On 3.9, this >> exploit works once uidmapping is added. >> >> http://www.openwall.com/lists/oss-security/2013/03/13/10 > > Yes. That is a bad combination. It let's chroot confuse privileged > processes. > > Now to figure out if this is easier to squash by adding a user_namespace > to fs_struct or by just forbidding this combination. It's worth making sure that setns(2) doesn't have similar issues. Looking through other shared-but-not-a-namespace things, there are: fs_struct: Buggy as noted. files_struct: Probably harmless -- SCM_RIGHTS can emulate it signal_struct: This interacts with the tty code. Is it okay? sighand_struct: Looks safe. Famous last words. FWIW, I've been alarmed in the past that struct path (e.g. the root directory) implies an mnt_namespace (hidden in struct mount), and it's entirely possible for the root directory's mnt_namespace not to match nsproxy->mnt_namespace. I'm not sure what the implications are, but this doesn't seem healthy. --Andy