From mboxrd@z Thu Jan 1 00:00:00 1970 From: ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org (Eric W. Biederman) Subject: Re: [PATCH v3] pid_ns: Introduce ioctl to set vector of ns_last_pid's on ns hierarhy Date: Thu, 27 Apr 2017 10:15:56 -0500 Message-ID: <87mvb16fv7.fsf@xmission.com> References: <149329634856.21195.14196911999722279118.stgit@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain Return-path: In-Reply-To: <149329634856.21195.14196911999722279118.stgit-bi+AKbBUZKY6gyzm1THtWbp2dZbC/Bob@public.gmane.org> (Kirill Tkhai's message of "Thu, 27 Apr 2017 15:32:46 +0300") Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Kirill Tkhai Cc: serge-A9i7LUbDfNHQT0dZR+AlfA@public.gmane.org, agruenba-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, oleg-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, paul-r2n+y4ga6xFZroRs9YW3xA@public.gmane.org, viro-RmSDqhL/yNMiFSDQTTA3OLVCufUGDwFn@public.gmane.org, avagin-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org, linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org, luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org, gorcunov-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org, mingo-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, keescook-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org List-Id: linux-api@vger.kernel.org Kirill Tkhai writes: > On implementing of nested pid namespaces support in CRIU > (checkpoint-restore in userspace tool) we run into > the situation, that it's impossible to create a task with > specific NSpid effectively. After commit 49f4d8b93ccf > "pidns: Capture the user namespace and filter ns_last_pid" > it is impossible to set ns_last_pid on any pid namespace, > except task's active pid_ns (before the commit it was possible > to write to pid_ns_for_children). Thus, if a restored task > in a container has more than one pid_ns levels, the restorer > code must have a task helper for every pid namespace > of the task's pid_ns hierarhy. > > This is a big problem, because of communication with > a helper for every pid_ns in the hierarchy is not cheap. > It's not performance-good as it implies many helpers wakeups > to create a single task (independently, how you communicate > with the helpers). This patch tries to decide the problem. I see the problem and we definitely need to do something. Your patch does appear better than what we have been doing. So a tenative conceptual ack. At the same time it is legitimate to claim that the use of task_active_pid_ns(current) rather than current->nsproxy->pid_ns_for_children is a regression caused by the above commit. So we can fix the original issue as well. I do have to ask when was this problem discovered, and why did it take so long to discover? The regeression happened nearly 5 years ago. Was CRIU already using this? It looks like the fix is a one line low danger change to /proc/sys/kernel/ns_last_pid. With a low danger as pid_ns_for_children rarely differs from task_active_pid_ns(). > It introduces a new pid_ns ioctl(NS_SET_LAST_PID_VEC), > which allows to write a vector of last pids on pid_ns hierarchy. > The vector is passed as array of pids in struct ns_ioc_pid_vec, > written in reverse order. The first number corresponds to > the opened namespace ns_last_pid, the second is to its parent, etc. > So, if you have the pid namespaces hierarchy like: > > pid_ns1 (grand father) > | > v > pid_ns2 (father) > | > v > pid_ns3 (child) > > and the pid_ns3 is open, then the corresponding vector will be > {last_ns_pid3, last_ns_pid2, last_ns_pid1}. This vector may be > short and it may contain less levels. For example, > {last_ns_pid3, last_ns_pid2} or even {last_ns_pid3}, in dependence > of which levels you want to populate. > > v3: Use __u32 in uapi instead of unsigned int. > > v2: Kill pid_ns->child_reaper check as it's impossible to have > such a pid namespace file open. > Use generic namespaces ioctl() number. > Pass pids as array, not as a string. > > Signed-off-by: Kirill Tkhai > --- > fs/nsfs.c | 5 +++++ > include/linux/pid_namespace.h | 12 ++++++++++++ > include/uapi/linux/nsfs.h | 7 +++++++ > kernel/pid_namespace.c | 35 +++++++++++++++++++++++++++++++++++ > 4 files changed, 59 insertions(+) > > diff --git a/fs/nsfs.c b/fs/nsfs.c > index 323f492e0822..f669a1552003 100644 > --- a/fs/nsfs.c > +++ b/fs/nsfs.c > @@ -6,6 +6,7 @@ > #include > #include > #include > +#include > #include > #include > > @@ -186,6 +187,10 @@ static long ns_ioctl(struct file *filp, unsigned int ioctl, > argp = (uid_t __user *) arg; > uid = from_kuid_munged(current_user_ns(), user_ns->owner); > return put_user(uid, argp); > + case NS_SET_LAST_PID_VEC: > + if (ns->ops->type != CLONE_NEWPID) > + return -EINVAL; > + return pidns_set_last_pid_vec(ns, (void *)arg); > default: > return -ENOTTY; > } > diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h > index c2a989dee876..c8dc4173a4e8 100644 > --- a/include/linux/pid_namespace.h > +++ b/include/linux/pid_namespace.h > @@ -9,6 +9,7 @@ > #include > #include > #include > +#include No need for the extra include and slowing down the build. Just declare the relevant structures. > > struct pidmap { > atomic_t nr_free; > @@ -103,6 +104,17 @@ static inline int reboot_pid_ns(struct pid_namespace *pid_ns, int cmd) > } > #endif /* CONFIG_PID_NS */ > > +#if defined(CONFIG_PID_NS) && defined(CONFIG_CHECKPOINT_RESTORE) > +extern long pidns_set_last_pid_vec(struct ns_common *ns, > + struct ns_ioc_pid_vec __user *vec); > +#else /* CONFIG_PID_NS && CONFIG_CHECKPOINT_RESTORE */ > +static inline long pidns_set_last_pid_vec(struct ns_common *ns, > + struct ns_ioc_pid_vec __user *vec) > +{ > + return -ENOTTY; > +} > +#endif /* CONFIG_PID_NS && CONFIG_CHECKPOINT_RESTORE */ Just CONFIG_PID_NS please. Either this is good enough for everyone who has pid namespace support enabled or it isn't. > extern struct pid_namespace *task_active_pid_ns(struct task_struct *tsk); > void pidhash_init(void); > void pidmap_init(void); > diff --git a/include/uapi/linux/nsfs.h b/include/uapi/linux/nsfs.h > index 1a3ca79f466b..1254b02a47fa 100644 > --- a/include/uapi/linux/nsfs.h > +++ b/include/uapi/linux/nsfs.h > @@ -14,5 +14,12 @@ > #define NS_GET_NSTYPE _IO(NSIO, 0x3) > /* Get owner UID (in the caller's user namespace) for a user namespace */ > #define NS_GET_OWNER_UID _IO(NSIO, 0x4) > +/* Set a vector of ns_last_pid for a pid namespace stack */ > +#define NS_SET_LAST_PID_VEC _IO(NSIO, 0x5) > + > +struct ns_ioc_pid_vec { > + __u32 nr; > + pid_t pid[0]; > +}; > > #endif /* __LINUX_NSFS_H */ > diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c > index de461aa0bf9a..08b5fef23534 100644 > --- a/kernel/pid_namespace.c > +++ b/kernel/pid_namespace.c > @@ -21,6 +21,7 @@ > #include > #include > #include > +#include > > struct pid_cache { > int nr_ids; > @@ -428,6 +429,40 @@ static struct ns_common *pidns_get_parent(struct ns_common *ns) > return &get_pid_ns(pid_ns)->ns; > } > > +#ifdef CONFIG_CHECKPOINT_RESTORE > +long pidns_set_last_pid_vec(struct ns_common *ns, > + struct ns_ioc_pid_vec __user *vec) > +{ > + struct pid_namespace *pid_ns = to_pid_ns(ns); > + pid_t pid, __user *pid_ptr; > + u32 nr; > + > + if (get_user(nr, &vec->nr)) > + return -EFAULT; > + if (nr > 32 || nr < 1) The maximum needs not to be hard coded. > + return -EINVAL; > + > + pid_ptr = &vec->pid[0]; All of the rest of the vector needs to be read in, in one go. > + do { > + if (!ns_capable(pid_ns->user_ns, CAP_SYS_ADMIN)) > + return -EPERM; Permission to change all of the namespaces should be checked before writing to pid_ns->last_pid happens. > + > + if (get_user(pid, pid_ptr)) > + return -EFAULT; > + if (pid < 0 || pid > pid_max) > + return -EINVAL; > + > + /* Write directly: see the comment in pid_ns_ctl_handler() */ > + pid_ns->last_pid = pid; > + > + pid_ns = pid_ns->parent; > + pid_ptr++; > + } while (--nr > 0 && pid_ns); > + > + return nr ? -EINVAL : 0; > +} > +#endif /* CONFIG_CHECKPOINT_RESTORE */ > + > static struct user_namespace *pidns_owner(struct ns_common *ns) > { > return to_pid_ns(ns)->user_ns; From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from out01.mta.xmission.com ([166.70.13.231]:53603 "EHLO out01.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965729AbdD0PWQ (ORCPT ); Thu, 27 Apr 2017 11:22:16 -0400 From: ebiederm@xmission.com (Eric W. Biederman) To: Kirill Tkhai Cc: , , , , , , , , , , , , , , , References: <149329634856.21195.14196911999722279118.stgit@localhost.localdomain> Date: Thu, 27 Apr 2017 10:15:56 -0500 In-Reply-To: <149329634856.21195.14196911999722279118.stgit@localhost.localdomain> (Kirill Tkhai's message of "Thu, 27 Apr 2017 15:32:46 +0300") Message-ID: <87mvb16fv7.fsf@xmission.com> MIME-Version: 1.0 Content-Type: text/plain Subject: Re: [PATCH v3] pid_ns: Introduce ioctl to set vector of ns_last_pid's on ns hierarhy Sender: linux-fsdevel-owner@vger.kernel.org List-ID: Kirill Tkhai writes: > On implementing of nested pid namespaces support in CRIU > (checkpoint-restore in userspace tool) we run into > the situation, that it's impossible to create a task with > specific NSpid effectively. After commit 49f4d8b93ccf > "pidns: Capture the user namespace and filter ns_last_pid" > it is impossible to set ns_last_pid on any pid namespace, > except task's active pid_ns (before the commit it was possible > to write to pid_ns_for_children). Thus, if a restored task > in a container has more than one pid_ns levels, the restorer > code must have a task helper for every pid namespace > of the task's pid_ns hierarhy. > > This is a big problem, because of communication with > a helper for every pid_ns in the hierarchy is not cheap. > It's not performance-good as it implies many helpers wakeups > to create a single task (independently, how you communicate > with the helpers). This patch tries to decide the problem. I see the problem and we definitely need to do something. Your patch does appear better than what we have been doing. So a tenative conceptual ack. At the same time it is legitimate to claim that the use of task_active_pid_ns(current) rather than current->nsproxy->pid_ns_for_children is a regression caused by the above commit. So we can fix the original issue as well. I do have to ask when was this problem discovered, and why did it take so long to discover? The regeression happened nearly 5 years ago. Was CRIU already using this? It looks like the fix is a one line low danger change to /proc/sys/kernel/ns_last_pid. With a low danger as pid_ns_for_children rarely differs from task_active_pid_ns(). > It introduces a new pid_ns ioctl(NS_SET_LAST_PID_VEC), > which allows to write a vector of last pids on pid_ns hierarchy. > The vector is passed as array of pids in struct ns_ioc_pid_vec, > written in reverse order. The first number corresponds to > the opened namespace ns_last_pid, the second is to its parent, etc. > So, if you have the pid namespaces hierarchy like: > > pid_ns1 (grand father) > | > v > pid_ns2 (father) > | > v > pid_ns3 (child) > > and the pid_ns3 is open, then the corresponding vector will be > {last_ns_pid3, last_ns_pid2, last_ns_pid1}. This vector may be > short and it may contain less levels. For example, > {last_ns_pid3, last_ns_pid2} or even {last_ns_pid3}, in dependence > of which levels you want to populate. > > v3: Use __u32 in uapi instead of unsigned int. > > v2: Kill pid_ns->child_reaper check as it's impossible to have > such a pid namespace file open. > Use generic namespaces ioctl() number. > Pass pids as array, not as a string. > > Signed-off-by: Kirill Tkhai > --- > fs/nsfs.c | 5 +++++ > include/linux/pid_namespace.h | 12 ++++++++++++ > include/uapi/linux/nsfs.h | 7 +++++++ > kernel/pid_namespace.c | 35 +++++++++++++++++++++++++++++++++++ > 4 files changed, 59 insertions(+) > > diff --git a/fs/nsfs.c b/fs/nsfs.c > index 323f492e0822..f669a1552003 100644 > --- a/fs/nsfs.c > +++ b/fs/nsfs.c > @@ -6,6 +6,7 @@ > #include > #include > #include > +#include > #include > #include > > @@ -186,6 +187,10 @@ static long ns_ioctl(struct file *filp, unsigned int ioctl, > argp = (uid_t __user *) arg; > uid = from_kuid_munged(current_user_ns(), user_ns->owner); > return put_user(uid, argp); > + case NS_SET_LAST_PID_VEC: > + if (ns->ops->type != CLONE_NEWPID) > + return -EINVAL; > + return pidns_set_last_pid_vec(ns, (void *)arg); > default: > return -ENOTTY; > } > diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h > index c2a989dee876..c8dc4173a4e8 100644 > --- a/include/linux/pid_namespace.h > +++ b/include/linux/pid_namespace.h > @@ -9,6 +9,7 @@ > #include > #include > #include > +#include No need for the extra include and slowing down the build. Just declare the relevant structures. > > struct pidmap { > atomic_t nr_free; > @@ -103,6 +104,17 @@ static inline int reboot_pid_ns(struct pid_namespace *pid_ns, int cmd) > } > #endif /* CONFIG_PID_NS */ > > +#if defined(CONFIG_PID_NS) && defined(CONFIG_CHECKPOINT_RESTORE) > +extern long pidns_set_last_pid_vec(struct ns_common *ns, > + struct ns_ioc_pid_vec __user *vec); > +#else /* CONFIG_PID_NS && CONFIG_CHECKPOINT_RESTORE */ > +static inline long pidns_set_last_pid_vec(struct ns_common *ns, > + struct ns_ioc_pid_vec __user *vec) > +{ > + return -ENOTTY; > +} > +#endif /* CONFIG_PID_NS && CONFIG_CHECKPOINT_RESTORE */ Just CONFIG_PID_NS please. Either this is good enough for everyone who has pid namespace support enabled or it isn't. > extern struct pid_namespace *task_active_pid_ns(struct task_struct *tsk); > void pidhash_init(void); > void pidmap_init(void); > diff --git a/include/uapi/linux/nsfs.h b/include/uapi/linux/nsfs.h > index 1a3ca79f466b..1254b02a47fa 100644 > --- a/include/uapi/linux/nsfs.h > +++ b/include/uapi/linux/nsfs.h > @@ -14,5 +14,12 @@ > #define NS_GET_NSTYPE _IO(NSIO, 0x3) > /* Get owner UID (in the caller's user namespace) for a user namespace */ > #define NS_GET_OWNER_UID _IO(NSIO, 0x4) > +/* Set a vector of ns_last_pid for a pid namespace stack */ > +#define NS_SET_LAST_PID_VEC _IO(NSIO, 0x5) > + > +struct ns_ioc_pid_vec { > + __u32 nr; > + pid_t pid[0]; > +}; > > #endif /* __LINUX_NSFS_H */ > diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c > index de461aa0bf9a..08b5fef23534 100644 > --- a/kernel/pid_namespace.c > +++ b/kernel/pid_namespace.c > @@ -21,6 +21,7 @@ > #include > #include > #include > +#include > > struct pid_cache { > int nr_ids; > @@ -428,6 +429,40 @@ static struct ns_common *pidns_get_parent(struct ns_common *ns) > return &get_pid_ns(pid_ns)->ns; > } > > +#ifdef CONFIG_CHECKPOINT_RESTORE > +long pidns_set_last_pid_vec(struct ns_common *ns, > + struct ns_ioc_pid_vec __user *vec) > +{ > + struct pid_namespace *pid_ns = to_pid_ns(ns); > + pid_t pid, __user *pid_ptr; > + u32 nr; > + > + if (get_user(nr, &vec->nr)) > + return -EFAULT; > + if (nr > 32 || nr < 1) The maximum needs not to be hard coded. > + return -EINVAL; > + > + pid_ptr = &vec->pid[0]; All of the rest of the vector needs to be read in, in one go. > + do { > + if (!ns_capable(pid_ns->user_ns, CAP_SYS_ADMIN)) > + return -EPERM; Permission to change all of the namespaces should be checked before writing to pid_ns->last_pid happens. > + > + if (get_user(pid, pid_ptr)) > + return -EFAULT; > + if (pid < 0 || pid > pid_max) > + return -EINVAL; > + > + /* Write directly: see the comment in pid_ns_ctl_handler() */ > + pid_ns->last_pid = pid; > + > + pid_ns = pid_ns->parent; > + pid_ptr++; > + } while (--nr > 0 && pid_ns); > + > + return nr ? -EINVAL : 0; > +} > +#endif /* CONFIG_CHECKPOINT_RESTORE */ > + > static struct user_namespace *pidns_owner(struct ns_common *ns) > { > return to_pid_ns(ns)->user_ns;