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 -- This message was distributed to subscribers of the selinux mailing list. If you no longer wish to subscribe, send mail to majordomo@xxxxxxxxxxxxx with the words "unsubscribe selinux" without quotes as the message.
