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![Eric W. Biederman](/assets/img/avatar_default.png)
Oleg pointed out that in a pid namespace the sequence. - pid 1 becomes a zombie - setns(thepidns), fork,... - reaping pid 1. - The injected processes exiting. Can lead to processes attempting access their child reaper and instead following a stale pointer. That waitpid for init can return before all of the processes in the pid namespace have exited is also unfortunate. Avoid these problems by disabling the allocation of new pids in a pid namespace when init dies, instead of when the last process in a pid namespace is reaped. Pointed-out-by: Oleg Nesterov <oleg@redhat.com> Reviewed-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
383 lines
8.8 KiB
C
383 lines
8.8 KiB
C
/*
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* Pid namespaces
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*
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* Authors:
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* (C) 2007 Pavel Emelyanov <xemul@openvz.org>, OpenVZ, SWsoft Inc.
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* (C) 2007 Sukadev Bhattiprolu <sukadev@us.ibm.com>, IBM
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* Many thanks to Oleg Nesterov for comments and help
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*
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*/
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#include <linux/pid.h>
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#include <linux/pid_namespace.h>
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#include <linux/user_namespace.h>
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#include <linux/syscalls.h>
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#include <linux/err.h>
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#include <linux/acct.h>
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#include <linux/slab.h>
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#include <linux/proc_fs.h>
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#include <linux/reboot.h>
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#include <linux/export.h>
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#define BITS_PER_PAGE (PAGE_SIZE*8)
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struct pid_cache {
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int nr_ids;
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char name[16];
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struct kmem_cache *cachep;
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struct list_head list;
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};
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static LIST_HEAD(pid_caches_lh);
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static DEFINE_MUTEX(pid_caches_mutex);
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static struct kmem_cache *pid_ns_cachep;
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/*
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* creates the kmem cache to allocate pids from.
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* @nr_ids: the number of numerical ids this pid will have to carry
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*/
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static struct kmem_cache *create_pid_cachep(int nr_ids)
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{
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struct pid_cache *pcache;
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struct kmem_cache *cachep;
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mutex_lock(&pid_caches_mutex);
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list_for_each_entry(pcache, &pid_caches_lh, list)
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if (pcache->nr_ids == nr_ids)
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goto out;
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pcache = kmalloc(sizeof(struct pid_cache), GFP_KERNEL);
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if (pcache == NULL)
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goto err_alloc;
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snprintf(pcache->name, sizeof(pcache->name), "pid_%d", nr_ids);
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cachep = kmem_cache_create(pcache->name,
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sizeof(struct pid) + (nr_ids - 1) * sizeof(struct upid),
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0, SLAB_HWCACHE_ALIGN, NULL);
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if (cachep == NULL)
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goto err_cachep;
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pcache->nr_ids = nr_ids;
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pcache->cachep = cachep;
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list_add(&pcache->list, &pid_caches_lh);
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out:
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mutex_unlock(&pid_caches_mutex);
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return pcache->cachep;
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err_cachep:
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kfree(pcache);
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err_alloc:
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mutex_unlock(&pid_caches_mutex);
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return NULL;
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}
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static void proc_cleanup_work(struct work_struct *work)
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{
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struct pid_namespace *ns = container_of(work, struct pid_namespace, proc_work);
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pid_ns_release_proc(ns);
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}
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/* MAX_PID_NS_LEVEL is needed for limiting size of 'struct pid' */
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#define MAX_PID_NS_LEVEL 32
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static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns,
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struct pid_namespace *parent_pid_ns)
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{
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struct pid_namespace *ns;
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unsigned int level = parent_pid_ns->level + 1;
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int i;
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int err;
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if (level > MAX_PID_NS_LEVEL) {
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err = -EINVAL;
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goto out;
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}
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err = -ENOMEM;
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ns = kmem_cache_zalloc(pid_ns_cachep, GFP_KERNEL);
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if (ns == NULL)
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goto out;
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ns->pidmap[0].page = kzalloc(PAGE_SIZE, GFP_KERNEL);
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if (!ns->pidmap[0].page)
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goto out_free;
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ns->pid_cachep = create_pid_cachep(level + 1);
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if (ns->pid_cachep == NULL)
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goto out_free_map;
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err = proc_alloc_inum(&ns->proc_inum);
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if (err)
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goto out_free_map;
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kref_init(&ns->kref);
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ns->level = level;
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ns->parent = get_pid_ns(parent_pid_ns);
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ns->user_ns = get_user_ns(user_ns);
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ns->nr_hashed = PIDNS_HASH_ADDING;
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INIT_WORK(&ns->proc_work, proc_cleanup_work);
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set_bit(0, ns->pidmap[0].page);
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atomic_set(&ns->pidmap[0].nr_free, BITS_PER_PAGE - 1);
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for (i = 1; i < PIDMAP_ENTRIES; i++)
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atomic_set(&ns->pidmap[i].nr_free, BITS_PER_PAGE);
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return ns;
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out_free_map:
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kfree(ns->pidmap[0].page);
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out_free:
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kmem_cache_free(pid_ns_cachep, ns);
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out:
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return ERR_PTR(err);
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}
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static void destroy_pid_namespace(struct pid_namespace *ns)
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{
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int i;
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proc_free_inum(ns->proc_inum);
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for (i = 0; i < PIDMAP_ENTRIES; i++)
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kfree(ns->pidmap[i].page);
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put_user_ns(ns->user_ns);
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kmem_cache_free(pid_ns_cachep, ns);
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}
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struct pid_namespace *copy_pid_ns(unsigned long flags,
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struct user_namespace *user_ns, struct pid_namespace *old_ns)
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{
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if (!(flags & CLONE_NEWPID))
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return get_pid_ns(old_ns);
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if (task_active_pid_ns(current) != old_ns)
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return ERR_PTR(-EINVAL);
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return create_pid_namespace(user_ns, old_ns);
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}
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static void free_pid_ns(struct kref *kref)
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{
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struct pid_namespace *ns;
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ns = container_of(kref, struct pid_namespace, kref);
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destroy_pid_namespace(ns);
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}
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void put_pid_ns(struct pid_namespace *ns)
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{
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struct pid_namespace *parent;
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while (ns != &init_pid_ns) {
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parent = ns->parent;
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if (!kref_put(&ns->kref, free_pid_ns))
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break;
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ns = parent;
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}
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}
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EXPORT_SYMBOL_GPL(put_pid_ns);
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void zap_pid_ns_processes(struct pid_namespace *pid_ns)
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{
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int nr;
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int rc;
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struct task_struct *task, *me = current;
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/* Don't allow any more processes into the pid namespace */
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disable_pid_allocation(pid_ns);
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/* Ignore SIGCHLD causing any terminated children to autoreap */
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spin_lock_irq(&me->sighand->siglock);
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me->sighand->action[SIGCHLD - 1].sa.sa_handler = SIG_IGN;
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spin_unlock_irq(&me->sighand->siglock);
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/*
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* The last thread in the cgroup-init thread group is terminating.
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* Find remaining pid_ts in the namespace, signal and wait for them
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* to exit.
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*
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* Note: This signals each threads in the namespace - even those that
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* belong to the same thread group, To avoid this, we would have
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* to walk the entire tasklist looking a processes in this
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* namespace, but that could be unnecessarily expensive if the
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* pid namespace has just a few processes. Or we need to
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* maintain a tasklist for each pid namespace.
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*
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*/
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read_lock(&tasklist_lock);
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nr = next_pidmap(pid_ns, 1);
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while (nr > 0) {
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rcu_read_lock();
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task = pid_task(find_vpid(nr), PIDTYPE_PID);
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if (task && !__fatal_signal_pending(task))
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send_sig_info(SIGKILL, SEND_SIG_FORCED, task);
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rcu_read_unlock();
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nr = next_pidmap(pid_ns, nr);
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}
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read_unlock(&tasklist_lock);
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/* Firstly reap the EXIT_ZOMBIE children we may have. */
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do {
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clear_thread_flag(TIF_SIGPENDING);
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rc = sys_wait4(-1, NULL, __WALL, NULL);
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} while (rc != -ECHILD);
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/*
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* sys_wait4() above can't reap the TASK_DEAD children.
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* Make sure they all go away, see free_pid().
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*/
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for (;;) {
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set_current_state(TASK_UNINTERRUPTIBLE);
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if (pid_ns->nr_hashed == 1)
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break;
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schedule();
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}
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__set_current_state(TASK_RUNNING);
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if (pid_ns->reboot)
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current->signal->group_exit_code = pid_ns->reboot;
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acct_exit_ns(pid_ns);
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return;
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}
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#ifdef CONFIG_CHECKPOINT_RESTORE
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static int pid_ns_ctl_handler(struct ctl_table *table, int write,
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void __user *buffer, size_t *lenp, loff_t *ppos)
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{
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struct pid_namespace *pid_ns = task_active_pid_ns(current);
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struct ctl_table tmp = *table;
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if (write && !ns_capable(pid_ns->user_ns, CAP_SYS_ADMIN))
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return -EPERM;
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/*
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* Writing directly to ns' last_pid field is OK, since this field
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* is volatile in a living namespace anyway and a code writing to
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* it should synchronize its usage with external means.
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*/
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tmp.data = &pid_ns->last_pid;
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return proc_dointvec_minmax(&tmp, write, buffer, lenp, ppos);
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}
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extern int pid_max;
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static int zero = 0;
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static struct ctl_table pid_ns_ctl_table[] = {
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{
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.procname = "ns_last_pid",
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.maxlen = sizeof(int),
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.mode = 0666, /* permissions are checked in the handler */
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.proc_handler = pid_ns_ctl_handler,
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.extra1 = &zero,
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.extra2 = &pid_max,
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},
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{ }
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};
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static struct ctl_path kern_path[] = { { .procname = "kernel", }, { } };
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#endif /* CONFIG_CHECKPOINT_RESTORE */
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int reboot_pid_ns(struct pid_namespace *pid_ns, int cmd)
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{
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if (pid_ns == &init_pid_ns)
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return 0;
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switch (cmd) {
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case LINUX_REBOOT_CMD_RESTART2:
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case LINUX_REBOOT_CMD_RESTART:
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pid_ns->reboot = SIGHUP;
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break;
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case LINUX_REBOOT_CMD_POWER_OFF:
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case LINUX_REBOOT_CMD_HALT:
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pid_ns->reboot = SIGINT;
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break;
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default:
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return -EINVAL;
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}
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read_lock(&tasklist_lock);
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force_sig(SIGKILL, pid_ns->child_reaper);
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read_unlock(&tasklist_lock);
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do_exit(0);
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/* Not reached */
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return 0;
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}
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static void *pidns_get(struct task_struct *task)
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{
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struct pid_namespace *ns;
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rcu_read_lock();
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ns = get_pid_ns(task_active_pid_ns(task));
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rcu_read_unlock();
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return ns;
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}
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static void pidns_put(void *ns)
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{
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put_pid_ns(ns);
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}
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static int pidns_install(struct nsproxy *nsproxy, void *ns)
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{
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struct pid_namespace *active = task_active_pid_ns(current);
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struct pid_namespace *ancestor, *new = ns;
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if (!ns_capable(new->user_ns, CAP_SYS_ADMIN) ||
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!nsown_capable(CAP_SYS_ADMIN))
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return -EPERM;
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/*
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* Only allow entering the current active pid namespace
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* or a child of the current active pid namespace.
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*
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* This is required for fork to return a usable pid value and
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* this maintains the property that processes and their
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* children can not escape their current pid namespace.
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*/
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if (new->level < active->level)
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return -EINVAL;
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ancestor = new;
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while (ancestor->level > active->level)
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ancestor = ancestor->parent;
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if (ancestor != active)
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return -EINVAL;
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put_pid_ns(nsproxy->pid_ns);
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nsproxy->pid_ns = get_pid_ns(new);
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return 0;
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}
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static unsigned int pidns_inum(void *ns)
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{
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struct pid_namespace *pid_ns = ns;
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return pid_ns->proc_inum;
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}
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const struct proc_ns_operations pidns_operations = {
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.name = "pid",
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.type = CLONE_NEWPID,
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.get = pidns_get,
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.put = pidns_put,
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.install = pidns_install,
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.inum = pidns_inum,
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};
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static __init int pid_namespaces_init(void)
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{
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pid_ns_cachep = KMEM_CACHE(pid_namespace, SLAB_PANIC);
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#ifdef CONFIG_CHECKPOINT_RESTORE
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register_sysctl_paths(kern_path, pid_ns_ctl_table);
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#endif
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return 0;
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}
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__initcall(pid_namespaces_init);
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