From mboxrd@z Thu Jan 1 00:00:00 1970 From: ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org (Eric W. Biederman) Subject: Re: CLONE_NEWUSER|CLONE_FS root exploit Date: Thu, 14 Mar 2013 13:29:10 -0700 Message-ID: <87hakdrai1.fsf@xmission.com> References: <20130313175729.GH12501@outflux.net> <87r4jjkv18.fsf@xmission.com> <51412C67.30908@mit.edu> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <51412C67.30908-3s7WtUTddSA@public.gmane.org> (Andy Lutomirski's message of "Wed, 13 Mar 2013 18:48:23 -0700") 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: Andy Lutomirski Cc: containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, Sebastian Krahmer , Kees Cook , Oleg Nesterov , Linux Kernel Mailing List List-Id: containers.vger.kernel.org Andy Lutomirski writes: > 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. setns(2) and unshare(2) are done and merged. See commit. commit e66eded8309ebf679d3d3c1f5820d1f2ca332c71 Author: Eric W. Biederman Date: Wed Mar 13 11:51:49 2013 -0700 userns: Don't allow CLONE_NEWUSER | CLONE_FS > 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? It should be. The tty code is heavily pid based, and CLONE_NEWPID requires !CLONE_VM (which implies !CLONE_SIGHAND and !CLONE_VM). > 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. The calls to check_mnt prevent abuse of the files found with fs_struct not matching the current mount namespace. static inline int check_mnt(struct mount *mnt) { return mnt->mnt_ns == current->nsproxy->mnt_ns; } Thanks for looking I know I did the same double take and wondered if I had missed anything else by accident when this bug showed up. So far even just looking it all over again I can't see anything. But I have clearly been blind before. Eric