Quelle pid_namespace.c Sprache: C

// SPDX-License-Identifier: GPL-2.0-only
/*
* Pid namespaces
*
* Authors:
*    (C) 2007 Pavel Emelyanov <xemul@openvz.org>, OpenVZ, SWsoft Inc.
*    (C) 2007 Sukadev Bhattiprolu <sukadev@us.ibm.com>, IBM
*     Many thanks to Oleg Nesterov for comments and help
*
*/

#include <linux/pid.h>
#include <linux/pid_namespace.h>
#include <linux/user_namespace.h>
#include <linux/syscalls.h>
#include <linux/cred.h>
#include <linux/err.h>
#include <linux/acct.h>
#include <linux/slab.h>
#include <linux/proc_ns.h>
#include <linux/reboot.h>
#include <linux/export.h>
#include <linux/sched/task.h>
#include <linux/sched/signal.h>
#include <linux/idr.h>
#include <uapi/linux/wait.h>
#include "pid_sysctl.h"

static DEFINE_MUTEX(pid_caches_mutex);
static struct kmem_cache *pid_ns_cachep;
/* Write once array, filled from the beginning. */
static struct kmem_cache *pid_cache[MAX_PID_NS_LEVEL];

/*
* creates the kmem cache to allocate pids from.
* @level: pid namespace level
*/

static struct kmem_cache *create_pid_cachep(unsigned int level)
{
/* Level 0 is init_pid_ns.pid_cachep */
struct kmem_cache **pkc = &pid_cache[level - 1];
struct kmem_cache *kc;
char name[4 + 10 + 1];
unsigned int len;

kc = READ_ONCE(*pkc);
if (kc)
  return kc;

snprintf(name, sizeof(name), "pid_%u", level + 1);
len = struct_size_t(struct pid, numbers, level + 1);
mutex_lock(&pid_caches_mutex);
/* Name collision forces to do allocation under mutex. */
if (!*pkc)
  *pkc = kmem_cache_create(name, len, 0,
      SLAB_HWCACHE_ALIGN | SLAB_ACCOUNT, NULL);
mutex_unlock(&pid_caches_mutex);
/* current can fail, but someone else can succeed. */
return READ_ONCE(*pkc);
}

static struct ucounts *inc_pid_namespaces(struct user_namespace *ns)
{
return inc_ucount(ns, current_euid(), UCOUNT_PID_NAMESPACES);
}

static void dec_pid_namespaces(struct ucounts *ucounts)
{
dec_ucount(ucounts, UCOUNT_PID_NAMESPACES);
}

static void destroy_pid_namespace_work(struct work_struct *work);

static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns,
struct pid_namespace *parent_pid_ns)
{
struct pid_namespace *ns;
unsigned int level = parent_pid_ns->level + 1;
struct ucounts *ucounts;
int err;

err = -EINVAL;
if (!in_userns(parent_pid_ns->user_ns, user_ns))
  goto out;

err = -ENOSPC;
if (level > MAX_PID_NS_LEVEL)
  goto out;
ucounts = inc_pid_namespaces(user_ns);
if (!ucounts)
  goto out;

err = -ENOMEM;
ns = kmem_cache_zalloc(pid_ns_cachep, GFP_KERNEL);
if (ns == NULL)
  goto out_dec;

idr_init(&ns->idr);

ns->pid_cachep = create_pid_cachep(level);
if (ns->pid_cachep == NULL)
  goto out_free_idr;

err = ns_alloc_inum(&ns->ns);
if (err)
  goto out_free_idr;
ns->ns.ops = &pidns_operations;

ns->pid_max = PID_MAX_LIMIT;
err = register_pidns_sysctls(ns);
if (err)
  goto out_free_inum;

refcount_set(&ns->ns.count, 1);
ns->level = level;
ns->parent = get_pid_ns(parent_pid_ns);
ns->user_ns = get_user_ns(user_ns);
ns->ucounts = ucounts;
ns->pid_allocated = PIDNS_ADDING;
INIT_WORK(&ns->work, destroy_pid_namespace_work);

#if defined(CONFIG_SYSCTL) && defined(CONFIG_MEMFD_CREATE)
ns->memfd_noexec_scope = pidns_memfd_noexec_scope(parent_pid_ns);
#endif

return ns;

out_free_inum:
ns_free_inum(&ns->ns);
out_free_idr:
idr_destroy(&ns->idr);
kmem_cache_free(pid_ns_cachep, ns);
out_dec:
dec_pid_namespaces(ucounts);
out:
return ERR_PTR(err);
}

static void delayed_free_pidns(struct rcu_head *p)
{
struct pid_namespace *ns = container_of(p, struct pid_namespace, rcu);

dec_pid_namespaces(ns->ucounts);
put_user_ns(ns->user_ns);

kmem_cache_free(pid_ns_cachep, ns);
}

static void destroy_pid_namespace(struct pid_namespace *ns)
{
unregister_pidns_sysctls(ns);

ns_free_inum(&ns->ns);

idr_destroy(&ns->idr);
call_rcu(&ns->rcu, delayed_free_pidns);
}

static void destroy_pid_namespace_work(struct work_struct *work)
{
struct pid_namespace *ns =
  container_of(work, struct pid_namespace, work);

do {
  struct pid_namespace *parent;

  parent = ns->parent;
  destroy_pid_namespace(ns);
  ns = parent;
} while (ns != &init_pid_ns && refcount_dec_and_test(&ns->ns.count));
}

struct pid_namespace *copy_pid_ns(unsigned long flags,
struct user_namespace *user_ns, struct pid_namespace *old_ns)
{
if (!(flags & CLONE_NEWPID))
  return get_pid_ns(old_ns);
if (task_active_pid_ns(current) != old_ns)
  return ERR_PTR(-EINVAL);
return create_pid_namespace(user_ns, old_ns);
}

void put_pid_ns(struct pid_namespace *ns)
{
if (ns && ns != &init_pid_ns && refcount_dec_and_test(&ns->ns.count))
  schedule_work(&ns->work);
}
EXPORT_SYMBOL_GPL(put_pid_ns);

void zap_pid_ns_processes(struct pid_namespace *pid_ns)
{
int nr;
int rc;
struct task_struct *task, *me = current;
int init_pids = thread_group_leader(me) ? 1 : 2;
struct pid *pid;

/* Don't allow any more processes into the pid namespace */
disable_pid_allocation(pid_ns);

/*
* Ignore SIGCHLD causing any terminated children to autoreap.
* This speeds up the namespace shutdown, plus see the comment
* below.
*/
spin_lock_irq(&me->sighand->siglock);
me->sighand->action[SIGCHLD - 1].sa.sa_handler = SIG_IGN;
spin_unlock_irq(&me->sighand->siglock);

/*
* The last thread in the cgroup-init thread group is terminating.
* Find remaining pid_ts in the namespace, signal and wait for them
* to exit.
*
* Note:  This signals each threads in the namespace - even those that
*   belong to the same thread group, To avoid this, we would have
*   to walk the entire tasklist looking a processes in this
*   namespace, but that could be unnecessarily expensive if the
*   pid namespace has just a few processes. Or we need to
*   maintain a tasklist for each pid namespace.
*
*/
rcu_read_lock();
read_lock(&tasklist_lock);
nr = 2;
idr_for_each_entry_continue(&pid_ns->idr, pid, nr) {
  task = pid_task(pid, PIDTYPE_PID);
  if (task && !__fatal_signal_pending(task))
   group_send_sig_info(SIGKILL, SEND_SIG_PRIV, task, PIDTYPE_MAX);
}
read_unlock(&tasklist_lock);
rcu_read_unlock();

/*
* Reap the EXIT_ZOMBIE children we had before we ignored SIGCHLD.
* kernel_wait4() will also block until our children traced from the
* parent namespace are detached and become EXIT_DEAD.
*/
do {
  clear_thread_flag(TIF_SIGPENDING);
  clear_thread_flag(TIF_NOTIFY_SIGNAL);
  rc = kernel_wait4(-1, NULL, __WALL, NULL);
} while (rc != -ECHILD);

/*
* kernel_wait4() misses EXIT_DEAD children, and EXIT_ZOMBIE
* process whose parents processes are outside of the pid
* namespace.  Such processes are created with setns()+fork().
*
* If those EXIT_ZOMBIE processes are not reaped by their
* parents before their parents exit, they will be reparented
* to pid_ns->child_reaper.  Thus pidns->child_reaper needs to
* stay valid until they all go away.
*
* The code relies on the pid_ns->child_reaper ignoring
* SIGCHILD to cause those EXIT_ZOMBIE processes to be
* autoreaped if reparented.
*
* Semantically it is also desirable to wait for EXIT_ZOMBIE
* processes before allowing the child_reaper to be reaped, as
* that gives the invariant that when the init process of a
* pid namespace is reaped all of the processes in the pid
* namespace are gone.
*
* Once all of the other tasks are gone from the pid_namespace
* free_pid() will awaken this task.
*/
for (;;) {
  set_current_state(TASK_INTERRUPTIBLE);
  if (pid_ns->pid_allocated == init_pids)
   break;
  schedule();
}
__set_current_state(TASK_RUNNING);

if (pid_ns->reboot)
  current->signal->group_exit_code = pid_ns->reboot;

acct_exit_ns(pid_ns);
return;
}

#ifdef CONFIG_CHECKPOINT_RESTORE
static int pid_ns_ctl_handler(const struct ctl_table *table, int write,
  void *buffer, size_t *lenp, loff_t *ppos)
{
struct pid_namespace *pid_ns = task_active_pid_ns(current);
struct ctl_table tmp = *table;
int ret, next;

if (write && !checkpoint_restore_ns_capable(pid_ns->user_ns))
  return -EPERM;

next = idr_get_cursor(&pid_ns->idr) - 1;

tmp.data = &next;
tmp.extra2 = &pid_ns->pid_max;
ret = proc_dointvec_minmax(&tmp, write, buffer, lenp, ppos);
if (!ret && write)
  idr_set_cursor(&pid_ns->idr, next + 1);

return ret;
}

static const struct ctl_table pid_ns_ctl_table[] = {
{
  .procname = "ns_last_pid",
  .maxlen = sizeof(int),
  .mode = 0666, /* permissions are checked in the handler */
  .proc_handler = pid_ns_ctl_handler,
  .extra1 = SYSCTL_ZERO,
  .extra2 = &init_pid_ns.pid_max,
},
};
#endif /* CONFIG_CHECKPOINT_RESTORE */

int reboot_pid_ns(struct pid_namespace *pid_ns, int cmd)
{
if (pid_ns == &init_pid_ns)
  return 0;

switch (cmd) {
case LINUX_REBOOT_CMD_RESTART2:
case LINUX_REBOOT_CMD_RESTART:
  pid_ns->reboot = SIGHUP;
  break;

case LINUX_REBOOT_CMD_POWER_OFF:
case LINUX_REBOOT_CMD_HALT:
  pid_ns->reboot = SIGINT;
  break;
default:
  return -EINVAL;
}

read_lock(&tasklist_lock);
send_sig(SIGKILL, pid_ns->child_reaper, 1);
read_unlock(&tasklist_lock);

do_exit(0);

/* Not reached */
return 0;
}

static inline struct pid_namespace *to_pid_ns(struct ns_common *ns)
{
return container_of(ns, struct pid_namespace, ns);
}

static struct ns_common *pidns_get(struct task_struct *task)
{
struct pid_namespace *ns;

rcu_read_lock();
ns = task_active_pid_ns(task);
if (ns)
  get_pid_ns(ns);
rcu_read_unlock();

return ns ? &ns->ns : NULL;
}

static struct ns_common *pidns_for_children_get(struct task_struct *task)
{
struct pid_namespace *ns = NULL;

task_lock(task);
if (task->nsproxy) {
  ns = task->nsproxy->pid_ns_for_children;
  get_pid_ns(ns);
}
task_unlock(task);

if (ns) {
  read_lock(&tasklist_lock);
  if (!ns->child_reaper) {
   put_pid_ns(ns);
   ns = NULL;
  }
  read_unlock(&tasklist_lock);
}

return ns ? &ns->ns : NULL;
}

static void pidns_put(struct ns_common *ns)
{
put_pid_ns(to_pid_ns(ns));
}

static int pidns_install(struct nsset *nsset, struct ns_common *ns)
{
struct nsproxy *nsproxy = nsset->nsproxy;
struct pid_namespace *active = task_active_pid_ns(current);
struct pid_namespace *ancestor, *new = to_pid_ns(ns);

if (!ns_capable(new->user_ns, CAP_SYS_ADMIN) ||
     !ns_capable(nsset->cred->user_ns, CAP_SYS_ADMIN))
  return -EPERM;

/*
* Only allow entering the current active pid namespace
* or a child of the current active pid namespace.
*
* This is required for fork to return a usable pid value and
* this maintains the property that processes and their
* children can not escape their current pid namespace.
*/
if (new->level < active->level)
  return -EINVAL;

ancestor = new;
while (ancestor->level > active->level)
  ancestor = ancestor->parent;
if (ancestor != active)
  return -EINVAL;

put_pid_ns(nsproxy->pid_ns_for_children);
nsproxy->pid_ns_for_children = get_pid_ns(new);
return 0;
}

static struct ns_common *pidns_get_parent(struct ns_common *ns)
{
struct pid_namespace *active = task_active_pid_ns(current);
struct pid_namespace *pid_ns, *p;

/* See if the parent is in the current namespace */
pid_ns = p = to_pid_ns(ns)->parent;
for (;;) {
  if (!p)
   return ERR_PTR(-EPERM);
  if (p == active)
   break;
  p = p->parent;
}

return &get_pid_ns(pid_ns)->ns;
}

static struct user_namespace *pidns_owner(struct ns_common *ns)
{
return to_pid_ns(ns)->user_ns;
}

const struct proc_ns_operations pidns_operations = {
.name  = "pid",
.type  = CLONE_NEWPID,
.get  = pidns_get,
.put  = pidns_put,
.install = pidns_install,
.owner  = pidns_owner,
.get_parent = pidns_get_parent,
};

const struct proc_ns_operations pidns_for_children_operations = {
.name  = "pid_for_children",
.real_ns_name = "pid",
.type  = CLONE_NEWPID,
.get  = pidns_for_children_get,
.put  = pidns_put,
.install = pidns_install,
.owner  = pidns_owner,
.get_parent = pidns_get_parent,
};

static __init int pid_namespaces_init(void)
{
pid_ns_cachep = KMEM_CACHE(pid_namespace, SLAB_PANIC | SLAB_ACCOUNT);

#ifdef CONFIG_CHECKPOINT_RESTORE
register_sysctl_init("kernel", pid_ns_ctl_table);
#endif

register_pid_ns_sysctl_table_vm();
return 0;
}

__initcall(pid_namespaces_init);

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