Messages in this thread | | | Subject | Re: [RESEND RFC] translate_pid API | From | Nagarathnam Muthusamy <> | Date | Tue, 13 Mar 2018 15:45:45 -0700 |
| |
On 03/13/2018 03:00 PM, Jann Horn wrote: > On Tue, Mar 13, 2018 at 2:44 PM, Nagarathnam Muthusamy > <nagarathnam.muthusamy@oracle.com> wrote: >> >> On 03/13/2018 02:28 PM, Jann Horn wrote: >>> On Tue, Mar 13, 2018 at 2:20 PM, Nagarathnam Muthusamy >>> <nagarathnam.muthusamy@oracle.com> wrote: >>>> On 03/13/2018 01:47 PM, Jann Horn wrote: >>>>> On Mon, Mar 12, 2018 at 10:18 AM, <nagarathnam.muthusamy@oracle.com> >>>>> wrote: >>>>>> Resending the RFC with participants of previous discussions >>>>>> in the list. >>>>>> >>>>>> Following patch which is a variation of a solution discussed >>>>>> in https://lwn.net/Articles/736330/ provides the users of >>>>>> pid namespace, the functionality of pid translation between >>>>>> namespaces using a namespace identifier. The topic of >>>>>> pid translation has been discussed in the community few times >>>>>> but there has always been a resistance to adding new solution >>>>>> for this problem. >>>>>> I will outline the planned usecase of pid namespace by oracle >>>>>> database and explain why any of the existing solution cannot >>>>>> be used to solve their problem. >>>>>> >>>>>> Consider a system in which several PID namespaces with multiple >>>>>> nested levels exists in parallel with monitor processes managing >>>>>> all the namespaces. PID translation is required for controlling >>>>>> and accessing information about the processes by the monitors >>>>>> and other processes down the hierarchy of namespaces. Controlling >>>>>> primarily involves sending signals or using ptrace by a process in >>>>>> parent namespace on any of the processes in its child namespace. >>>>>> Accessing information deals with the reading /proc/<pid>/* files >>>>>> of processes in child namespace. None of the processes have >>>>>> root/CAP_SYS_ADMIN privileges. >>>>> How are you dealing with PID reuse? >>>> >>>> We have a monitor process which keeps track of the aliveness of >>>> important processes. When a process dies, monitor makes a note of >>>> it and hence detects if pid is reused. >>> How do you do that in a race-free manner? >> >> AFAIK, the monitor runs periodically to check the aliveness of the processes >> and this period is too short for pids to recycle. I will get back with more >> information >> on this if any other mechanisms are in place. >> >> >>> >>>>>> + */ >>>>>> +SYSCALL_DEFINE3(translate_pid, pid_t, pid, u64, source, >>>>>> + u64, target) >>>>>> +{ >>>>>> + struct pid_namespace *source_ns = NULL, *target_ns = NULL; >>>>>> + struct pid *struct_pid; >>>>>> + struct pid_namespace *ph; >>>>>> + struct hlist_bl_head *shead = NULL; >>>>>> + struct hlist_bl_head *thead = NULL; >>>>>> + struct hlist_bl_node *dup_node; >>>>>> + pid_t result; >>>>>> + >>>>>> + if (!source) { >>>>>> + source_ns = &init_pid_ns; >>>>>> + } else { >>>>>> + shead = pid_ns_hash_head(pid_ns_hash, source); >>>>>> + hlist_bl_lock(shead); >>>>>> + hlist_bl_for_each_entry(ph, dup_node, shead, node) { >>>>>> + if (source == ph->ns.ns_id) { >>>>>> + source_ns = ph; >>>>>> + break; >>>>>> + } >>>>>> + } >>>>>> + if (!source_ns) { >>>>>> + hlist_bl_unlock(shead); >>>>>> + return -EINVAL; >>>>>> + } >>>>>> + } >>>>>> + if (!ptrace_may_access(source_ns->child_reaper, >>>>>> + PTRACE_MODE_READ_FSCREDS)) { >>>>> AFAICS this proposal breaks the visibility restrictions that >>>>> namespaces normally create. If there are two namespaces-based >>>>> containers that use the same UID range, I don't think they should be >>>>> able to learn information about each other, such as which PIDs are in >>>>> use in the other container; but as far as I can tell, your proposal >>>>> makes it possible to do that (unless an LSM or so is interfering). I >>>>> would prefer it if this API required visibility of the targeted PID >>>>> namespaces in the caller's PID namespace. >>>> >>>> I am trying to simulate the same access restrictions allowed >>>> on a process's /proc/<pid>/ns/pid file. If the translator has >>>> access to /proc/<pid>/ns/pid file of both source and destination >>>> namespaces, shouldn't it be allowed to translate the pid between >>>> them? >>> But the translator doesn't actually need to have access to those >>> procfs files, right? >> I thought it should have access to those procfs files to satisfy the >> visibility constraint that targeted PID namespaces should be visible >> in caller's PID namespace and ptrace_may_access checks that >> constraint. > If there are two containers that use the same UID range, > ptrace_may_access() checks from a process in one container on a > process in another container can pass. Normally, you just can't even > reach the ptrace_may_access() checks because you can't reference > processes in another container in any way.
If there is no way to reference the process in another container, there is no way to get to the /proc/<pid>/ns/pidns_id file which exports the ID of that container right? So, a translator has to first guess the container ID then try translate. Even after translation, unless the translator has proper privileges, I believe it cant do anything with just the pid right?
> > By the way, a related concern: The use of global identifiers will > probably also negatively affect Checkpoint/Restore In Userspace? Will look into this. Can you point me to the specifics of the usecase which could be negatively affected?
Thanks, Nagarathnam.
| |