Messages in this thread | | | Subject | Re: [RESEND RFC] translate_pid API | From | Nagarathnam Muthusamy <> | Date | Tue, 13 Mar 2018 14:44:17 -0700 |
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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.
Thanks, Nagarathnam.
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