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.
It introduces a new pid_ns ioctl(NS_SET_LAST_PID_VEC),
which allows to set 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
shorter 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.
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 <ktkhai@xxxxxxxxxxxxx>
---
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 <linux/ktime.h>
#include <linux/seq_file.h>
#include <linux/user_namespace.h>
+#include <linux/pid_namespace.h>
#include <linux/nsfs.h>
#include <linux/uaccess.h>
@@ -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 <linux/nsproxy.h>
#include <linux/kref.h>
#include <linux/ns_common.h>
+#include <uapi/linux/nsfs.h>
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 */
+
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..59adf97d1d63 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 {
+ unsigned int nr;
+ pid_t pid[0];
+};
#endif /* __LINUX_NSFS_H */
diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
index de461aa0bf9a..f68ee8793606 100644
--- a/kernel/pid_namespace.c
+++ b/kernel/pid_namespace.c
@@ -21,6 +21,7 @@
#include <linux/export.h>
#include <linux/sched/task.h>
#include <linux/sched/signal.h>
+#include <uapi/linux/nsfs.h>
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;
+ unsigned int nr;
+
+ if (get_user(nr, &vec->nr))
+ return -EFAULT;
+ if (nr > 32 || nr < 1)
+ return -EINVAL;
+
+ pid_ptr = &vec->pid[0];
+ do {
+ if (!ns_capable(pid_ns->user_ns, CAP_SYS_ADMIN))
+ return -EPERM;
+
+ 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;
