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Date: Tue, 15 Sep 2015 18:01:38 +0300
From: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
To: "Eric W. Biederman" <ebiederm@...ssion.com>
Cc: linux-api@...r.kernel.org, containers@...ts.linux-foundation.org,
linux-kernel@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH RFC] pidns: introduce syscall getvpid
On 15.09.2015 17:27, Eric W. Biederman wrote:
> Konstantin Khlebnikov <khlebnikov@...dex-team.ru> writes:
>
>> pid_t getvpid(pid_t pid, pid_t source, pid_t target);
>>
>> This syscall converts pid from one pid-ns into pid in another pid-ns:
>> it takes @pid in namespace of @source task (zero for current) and
>> returns related pid in namespace of @target task (zero for current too).
>> If pid is unreachable from target pid-ns then it returns zero.
>
> This interface as presented is inherently racy. It would be better
> if source and target were file descriptors referring to the namespaces
> you wish to translate between.
Yep, it's racy. As well as any operation with non-child pids.
With file descriptors for source/target result will be racy anyway.
>
>> Such conversion is required for interaction between processes from
>> different pid-namespaces. For example when system service talks with
>> client from isolated container via socket about task in container:
>
> Sockets are already supported. At least the metadata of sockets is.
>
> Maybe we need this but I am not convinced of it's utility.
>
> What are you trying to do that motivates this?
I'm working on hierarchical container management system which
allows to create and control nested sub-containers from containers
( https://github.com/yandex/porto ). Main server works in host and
have to interact with all levels of nested namespaces. This syscall
makes some operations much easier: server must remember only pid in
host pid namespace and convert it into right vpid on demand.
>
> Eric
>
>
>> getvpid(pid, client_pid, 0) -> pid in our pid namespace
>> getvpid(pid, 0, client_pid) -> pid in client pid namespace
>>
>> Also service can get pid of init task and match it with container:
>>
>> getvpid(1, client_pid, 0) -> pid of init task for client_pid
>>
>> Seems like gdb and strace could use this too for converting pids of
>> newly forked tasks (IIRR they get pid from %rax) into pid from
>> correct namespace for further interaction.
>>
>> As a bonus syscall getvpid can compare pid namespaces and
>> test isolation without mounted procfs:
>>
>> getvpid(1, 0, pid) == 0 -> pid in our sub-pid-namespace
>> getvpid(1, 0, pid) == 1 -> pid in our pid-namespace
>> getvpid(1, pid1, pid2) == 0 -> pid1 isolated from pid2
>> getvpid(1, pid1, pid2) == 1 -> tasks are in one pid-namespace
>> getvpid(1, pid1, pid2) > 1 -> pid1 is in sub-pidns of pid2
>>
>> Signed-off-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
>> ---
>> arch/x86/entry/syscalls/syscall_32.tbl | 1 +
>> arch/x86/entry/syscalls/syscall_64.tbl | 1 +
>> include/linux/syscalls.h | 1 +
>> kernel/pid.c | 36 ++++++++++++++++++++++++++++++++
>> 4 files changed, 39 insertions(+)
>>
>> diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
>> index 7663c455b9f6..dadb55d42fc9 100644
>> --- a/arch/x86/entry/syscalls/syscall_32.tbl
>> +++ b/arch/x86/entry/syscalls/syscall_32.tbl
>> @@ -382,3 +382,4 @@
>> 373 i386 shutdown sys_shutdown
>> 374 i386 userfaultfd sys_userfaultfd
>> 375 i386 membarrier sys_membarrier
>> +376 i386 getvpid sys_getvpid
>> diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
>> index 278842fdf1f6..0338f2eb3b7c 100644
>> --- a/arch/x86/entry/syscalls/syscall_64.tbl
>> +++ b/arch/x86/entry/syscalls/syscall_64.tbl
>> @@ -331,6 +331,7 @@
>> 322 64 execveat stub_execveat
>> 323 common userfaultfd sys_userfaultfd
>> 324 common membarrier sys_membarrier
>> +325 common getvpid sys_getvpid
>>
>> #
>> # x32-specific system call numbers start at 512 to avoid cache impact
>> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
>> index a460e2ef2843..3405c30999e3 100644
>> --- a/include/linux/syscalls.h
>> +++ b/include/linux/syscalls.h
>> @@ -222,6 +222,7 @@ asmlinkage long sys_nanosleep(struct timespec __user *rqtp, struct timespec __us
>> asmlinkage long sys_alarm(unsigned int seconds);
>> asmlinkage long sys_getpid(void);
>> asmlinkage long sys_getppid(void);
>> +asmlinkage long sys_getvpid(pid_t pid, pid_t source, pid_t target);
>> asmlinkage long sys_getuid(void);
>> asmlinkage long sys_geteuid(void);
>> asmlinkage long sys_getgid(void);
>> diff --git a/kernel/pid.c b/kernel/pid.c
>> index ca368793808e..caa676ff7364 100644
>> --- a/kernel/pid.c
>> +++ b/kernel/pid.c
>> @@ -567,6 +567,42 @@ struct pid *find_ge_pid(int nr, struct pid_namespace *ns)
>> return pid;
>> }
>>
>> +/**
>> + * sys_getvpid - convert pid from one pid-namespace into pid from another
>> + *
>> + * @pid - pid of requested task
>> + * @source - pid of task in source pid-namespace, zero for current
>> + * @target - pid of task in target pid-namespace, zero for current
>> + *
>> + * Returns pid from target pid-ns or zero if pid is unreachable.
>> + * Returns -ESRCH if some of pids are not found.
>> + */
>> +SYSCALL_DEFINE3(getvpid, pid_t, pid, pid_t, source, pid_t, target)
>> +{
>> +#ifdef CONFIG_PID_NS
>> + struct pid_namespace *current_ns = task_active_pid_ns(current);
>> + struct pid_namespace *source_ns = current_ns, *target_ns = current_ns;
>> + struct pid *task_pid;
>> + pid_t result = -ESRCH;
>> +
>> + rcu_read_lock();
>> + if (source)
>> + source_ns = ns_of_pid(find_pid_ns(source, current_ns));
>> + if (target)
>> + target_ns = ns_of_pid(find_pid_ns(target, current_ns));
>> + if (source_ns && target_ns) {
>> + task_pid = find_pid_ns(pid, source_ns);
>> + if (task_pid)
>> + result = pid_nr_ns(task_pid, target_ns);
>> + }
>> + rcu_read_unlock();
>> +
>> + return result;
>> +#else
>> + return pid;
>> +#endif /* CONFIG_PID_NS */
>> +}
>> +
>> /*
>> * The pid hash table is scaled according to the amount of memory in the
>> * machine. From a minimum of 16 slots up to 4096 slots at one gigabyte or
--
Konstantin
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