From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Serge E. Hallyn" Subject: Re: [REVIEW][PATCH 3/5] pidns: Don't have unshare(CLONE_NEWPID) imply CLONE_THREAD Date: Sat, 31 Aug 2013 05:31:25 +0000 Message-ID: <20130831053125.GA24025@mail.hallyn.com> References: <87ob8gys0d.fsf@xmission.com> <87a9k0yrvu.fsf@xmission.com> <20130830163805.GB18857@mail.hallyn.com> <87ppsuviwb.fsf@xmission.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <87ppsuviwb.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: Linux Containers , Oleg Nesterov , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: containers.vger.kernel.org Quoting Eric W. Biederman (ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org): > "Serge E. Hallyn" writes: > > > Quoting Eric W. Biederman (ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org): > >> > >> I goofed when I made unshare(CLONE_NEWPID) only work in a > >> single-threaded process. There is no need for that requirement and in > >> fact I analyzied things right for setns. The hard requirement > >> is for tasks that share a VM to all be in the pid namespace and > >> we properly prevent that in do_fork. > > > > I don't understand though - copy_process does have the right test: > > > > 1176 * If the new process will be in a different pid namespace > > 1177 * don't allow the creation of threads. > > 1178 */ > > 1179 if ((clone_flags & (CLONE_VM|CLONE_NEWPID)) && > > 1180 (task_active_pid_ns(current) != current->nsproxy->pid_ns)) > > 1181 return ERR_PTR(-EINVAL); > > > > but why is it ok for sys_unshare not to do that? Note that > > in order for check_unshare_flags() to bail on ¤t->mm->mm_users > 1 > > you do have to set CLONE_VM (for inverse interpretation). > > > > So it seems to me this isn't safe as is, and we need to at least > > set CLONE_VM if CLONE_PID is set. > > Partly this is the difference in the meaning of the flags between > unshare and clone. > > Basically in unshare all othat gets changed is > current->nsproxy->pid_ns_for_children (the rename is in the net tree). D'oh, right. Thanks! Acked-by: Serge Hallyn > So because unshare of the pid namespace does not actually effect the > current processes, just the pid namespace the children of the current > thread will be in this is safe. > > And frankly having the checks be obviously different is a good thing > because it means that people will ask why in the world this is so and > realize the difference in meaning. > > Eric