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
and 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 ns_ioctl(PIDNS_REQ_SET_LAST_PID_VEC),
which allows to write a vector of last pids on pid_ns hierarchy.
The vector is passed as a ":"-delimited string with pids,
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 ns of task's of 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.
To write in a pid_ns's ns_last_pid we check that the writer task
has CAP_SYS_ADMIN permittions in this pid_ns's user_ns.
One note about struct pidns_ioc_req. It's made extensible and
may expanded in the future. The always existing fields present
at the moment, the future fields and they sizes may be determined
by pidns_ioc_req::req by the future code.
Signed-off-by: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx>
---
include/uapi/linux/nsfs.h | 9 +++++
kernel/pid_namespace.c | 88 +++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 97 insertions(+)
diff --git a/include/uapi/linux/nsfs.h b/include/uapi/linux/nsfs.h
index 544bbb661475..37bb4af917b5 100644
--- a/include/uapi/linux/nsfs.h
+++ b/include/uapi/linux/nsfs.h
@@ -17,4 +17,13 @@
/* Execute namespace-specific ioctl */
#define NS_SPECIFIC_IOC _IO(NSIO, 0x5)
+struct pidns_ioc_req {
+/* Set vector of last pids in namespace hierarchy */
+#define PIDNS_REQ_SET_LAST_PID_VEC 0x1
+ unsigned int req;
+ void __user *data;
+ unsigned int data_size;
+ char std_fields[0];
+};
+
#endif /* __LINUX_NSFS_H */
diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
index de461aa0bf9a..0e86fa15cd92 100644
--- a/kernel/pid_namespace.c
+++ b/kernel/pid_namespace.c
@@ -21,6 +21,8 @@
#include <linux/export.h>
#include <linux/sched/task.h>
#include <linux/sched/signal.h>
+#include <linux/vmalloc.h>
+#include <uapi/linux/nsfs.h>
struct pid_cache {
int nr_ids;
@@ -428,6 +430,91 @@ static struct ns_common *pidns_get_parent(struct ns_common *ns)
return &get_pid_ns(pid_ns)->ns;
}
+#ifdef CONFIG_CHECKPOINT_RESTORE
+static long set_last_pid_vec(struct pid_namespace *pid_ns,
+ struct pidns_ioc_req *req)
+{
+ char *str, *p;
+ int ret = 0;
+ pid_t pid;
+
+ read_lock(&tasklist_lock);
+ if (!pid_ns->child_reaper)
+ ret = -EINVAL;
+ read_unlock(&tasklist_lock);
+ if (ret)
+ return ret;
+
+ if (req->data_size >= PAGE_SIZE)
+ return -EINVAL;
+ str = vmalloc(req->data_size + 1);
+ if (!str)
+ return -ENOMEM;
+ if (copy_from_user(str, req->data, req->data_size)) {
+ ret = -EFAULT;
+ goto out_vfree;
+ }
+ str[req->data_size] = '\0';
+
+ p = str;
+ while (p && *p != '\0') {
+ if (!ns_capable(pid_ns->user_ns, CAP_SYS_ADMIN)) {
+ ret = -EPERM;
+ goto out_vfree;
+ }
+
+ if (sscanf(p, "%d", &pid) != 1 || pid < 0 || pid > pid_max) {
+ ret = -EINVAL;
+ goto out_vfree;
+ }
+
+ /* Write directly: see the comment in pid_ns_ctl_handler() */
+ pid_ns->last_pid = pid;
+
+ p = strchr(p, ':');
+ pid_ns = pid_ns->parent;
+ if (p) {
+ if (!pid_ns) {
+ ret = -EINVAL;
+ goto out_vfree;
+ }
+ p++;
+ }
+ }
+
+ ret = 0;
+out_vfree:
+ vfree(str);
+ return ret;
+}
+#else /* CONFIG_CHECKPOINT_RESTORE */
+static long set_last_pid_vec(struct pid_namespace *pid_ns,
+ struct pidns_ioc_req *req)
+{
+ return -ENOTTY;
+}
+#endif /* CONFIG_CHECKPOINT_RESTORE */
+
+static long pidns_ioctl(struct ns_common *ns, unsigned long arg)
+{
+ struct pid_namespace *pid_ns = to_pid_ns(ns);
+ struct pidns_ioc_req user_req;
+ int ret;
+
+ ret = copy_from_user(&user_req, (void *)arg,
+ offsetof(struct pidns_ioc_req, std_fields));
+ if (ret)
+ return ret;
+
+ switch (user_req.req) {
+ case PIDNS_REQ_SET_LAST_PID_VEC:
+ return set_last_pid_vec(pid_ns, &user_req);
+ default:
+ return -ENOTTY;
+ }
+ return 0;
+}
+
static struct user_namespace *pidns_owner(struct ns_common *ns)
{
return to_pid_ns(ns)->user_ns;
@@ -441,6 +528,7 @@ const struct proc_ns_operations pidns_operations = {
.install = pidns_install,
.owner = pidns_owner,
.get_parent = pidns_get_parent,
+ .ns_ioctl = pidns_ioctl,
};
static __init int pid_namespaces_init(void)
