Hi Paul and Eric, Do you guys have any objections to dropping the hijack_pid() and hijack_cgroup() parts of sys_hijack, leaving just hijack_ns() (see below for discussion)? Thanks! Mark. Serge E. Hallyn wrote: > Quoting Stephen Smalley (sds@xxxxxxxxxxxxx): >> On Tue, 2007-11-27 at 16:38 -0600, Serge E. Hallyn wrote: >>> Quoting Stephen Smalley (sds@xxxxxxxxxxxxx): >>>> On Tue, 2007-11-27 at 10:11 -0600, Serge E. Hallyn wrote: >>>>> Quoting Crispin Cowan (crispin@xxxxxxxxxxxxxxxx): >>>>>> Just the name "sys_hijack" makes me concerned. >>>>>> >>>>>> This post describes a bunch of "what", but doesn't tell us about "why" >>>>>> we would want this. What is it for? >>>>> Please see my response to Casey's email. >>>>> >>>>>> And I second Casey's concern about careful management of the privilege >>>>>> required to "hijack" a process. >>>>> Absolutely. We're definately still in RFC territory. >>>>> >>>>> Note that there are currently several proposed (but no upstream) ways to >>>>> accomplish entering a namespace: >>>>> >>>>> 1. bind_ns() is a new pair of syscalls proposed by Cedric. An >>>>> nsproxy is given an integer id. The id can be used to enter >>>>> an nsproxy, basically a straight current->nsproxy = target_nsproxy; >>>>> >>>>> 2. I had previously posted a patchset on top of the nsproxy >>>>> cgroup which allowed entering a nsproxy through the ns cgroup >>>>> interface. >>>>> >>>>> There are objections to both those patchsets because simply switching a >>>>> task's nsproxy using a syscall or file write in the middle of running a >>>>> binary is quite unsafe. Eric Biederman had suggested using ptrace or >>>>> something like it to accomplish the goal. >>>>> >>>>> Just using ptrace is however not safe either. You are inheriting *all* >>>>> of the target's context, so it shouldn't be difficult for a nefarious >>>>> container/vserver admin to trick the host admin into running something >>>>> which gives the container/vserver admin full access to the host. >>>> I don't follow the above - with ptrace, you are controlling a process >>>> already within the container (hence in theory already limited to its >>>> container), and it continues to execute within that container. What's >>>> the issue there? >>> Hmm, yeah, I may have overspoken - I'm not good at making up exploits >>> but while I see it possible to confuse the host admin by setting bogus >>> environment, I guess there may not be an actual exploit. >>> >>> Still after the fork induced through ptrace, we'll have to execute a >>> file out of the hijacked process' namespaces and path (unless we get >>> *really* 'exotic'). With hijack, execution continues under the caller's >>> control, which I do much prefer. >>> >>> The remaining advantages of hijack over ptrace (beside "using ptrace for >>> that is crufty") are >>> >>> 1. not subject to pid wraparound (when doing hijack_cgroup >>> or hijack_ns) >>> 2. ability to enter a namespace which has no active processes >> So possibly I'm missing something, but the situation with hijack seems >> more exploitable than ptrace to me - you've created a hybrid task with >> one foot in current's world (open files, tty, connection to parent, >> executable) and one foot in the target's world (namespaces, uid/gid) >> which can then be leveraged by other tasks within the target's >> world/container as a way of breaking out of the container. No? > > I *think* the things coming out of the new container are well enough > chosen to prevent that. I see where you're opening up to being killed > by a task in the target container, though. But apart from setting a > PF_FLAG I'm not sure how to stop that anyway. > > This actually reminds me that we need a valid uid in the target > namespace in the HIJACK_NS case. It's not a problem right now, but > as I was just looking at fixing up kernel/signal.c in light of user > namespaces, it is something to keep in mind. > >>> These also highlight selinux issues. In the case of hijacking an >>> empty cgroup, there is no security context (because there is no task) so >>> the context of 'current' will be used. In the case of hijacking a >>> populated cgroup, a task is chosen "at random" to be the hijack source. >> Seems like you might be better off with a single operation for creating >> a new task within a given namespace set / cgroup rather than trying to >> handle multiple situations with different semantics / inheritance >> behavior. IOW, forget about hijacking a specific pid or picking a task >> at random from a populated cgroup - just always initialize the state of >> the newly created task in the same manner based solely on elements of >> the caller's state and the cgroup's state. > > So you're saying implement only the HIJACK_NS? > > I'm fine with that. Does anyone on the containers list object? > >>> So there are two ways to look at deciding which context to use. Since >>> control continues in the original acting process' context, we might >>> want the child to continue in its context. However if the process >>> creates any objects in the virtual server, we don't want them >>> mislabeled, so we might want the task in the hijacked task's context. >> I suspect that we want to continue in the parent's context, and then the >> program can always use setfscreatecon() or exec a helper in a different >> context if it wants to create files with contexts tailored to the >> target. > > That sounds good to me... > > So we're looking at: > > 1. drop HIJACK_PID and HIJACK_CGROUP > > 2. have selinux_task_alloc_security() always set task->security > to current->security and allow the hijack case. > > thanks, > -serge > _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers