From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nagarathnam Muthusamy Subject: Re: [RESEND RFC] translate_pid API Date: Tue, 13 Mar 2018 16:52:40 -0700 Message-ID: <65625f8c-d701-7407-3999-6ca30a59c236@oracle.com> References: <1520875093-18174-1-git-send-email-nagarathnam.muthusamy@oracle.com> <69f13674-7f84-5dc7-0bd7-e5e65e9cb3b0@oracle.com> <1a8cac8b-22cc-e194-4244-b20428c8a9c2@oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Jann Horn Cc: kernel list , Linux API , Konstantin Khlebnikov , Nagarajan.Muthukrishnan@oracle.com, Prakash Sangappa , Andy Lutomirski , Andrew Morton , Oleg Nesterov , Serge Hallyn , "Eric W. Biederman" , Eugene Syromiatnikov , xemul@parallels.com List-Id: linux-api@vger.kernel.org On 03/13/2018 04:10 PM, Jann Horn wrote: > On Tue, Mar 13, 2018 at 3:45 PM, Nagarathnam Muthusamy > wrote: >> On 03/13/2018 03:00 PM, Jann Horn wrote: >>> On Tue, Mar 13, 2018 at 2:44 PM, Nagarathnam Muthusamy >>> wrote: >>>> On 03/13/2018 02:28 PM, Jann Horn wrote: >>>>> On Tue, Mar 13, 2018 at 2:20 PM, Nagarathnam Muthusamy >>>>> wrote: >>>>>> On 03/13/2018 01:47 PM, Jann Horn wrote: >>>>>>> On Mon, Mar 12, 2018 at 10:18 AM, >>>>>>> wrote: > [...] >>>>>>>> + */ >>>>>>>> +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//ns/pid file. If the translator has >>>>>> access to /proc//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//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? > Well, yes to both. You'd have to guess the ID of the container, and > you wouldn't be able to do much with it, apart from finding valid PIDs > and their mapping between namespaces. > >>> 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? > AFAICS you won't be able to reliably recreate namespace IDs when a > process is checkpointed and resumed, meaning that checkpoint/resume > won't work on processes that use these namespace IDs. I agree. When the process is resumed, the namespace IDs might be obsolete. Thanks, Nagarathnam.