![Eric W. Biederman](/assets/img/avatar_default.png)
Unsharing of the pid namespace unlike unsharing of other namespaces does not take affect immediately. Instead it affects the children created with fork and clone. The first of these children becomes the init process of the new pid namespace, the rest become oddball children of pid 0. From the point of view of the new pid namespace the process that created it is pid 0, as it's pid does not map. A couple of different semantics were considered but this one was settled on because it is easy to implement and it is usable from pam modules. The core reasons for the existence of unshare. I took a survey of the callers of pam modules and the following appears to be a representative sample of their logic. { setup stuff include pam child = fork(); if (!child) { setuid() exec /bin/bash } waitpid(child); pam and other cleanup } As you can see there is a fork to create the unprivileged user space process. Which means that the unprivileged user space process will appear as pid 1 in the new pid namespace. Further most login processes do not cope with extraneous children which means shifting the duty of reaping extraneous child process to the creator of those extraneous children makes the system more comprehensible. The practical reason for this set of pid namespace semantics is that it is simple to implement and verify they work correctly. Whereas an implementation that requres changing the struct pid on a process comes with a lot more races and pain. Not the least of which is that glibc caches getpid(). These semantics are implemented by having two notions of the pid namespace of a proces. There is task_active_pid_ns which is the pid namspace the process was created with and the pid namespace that all pids are presented to that process in. The task_active_pid_ns is stored in the struct pid of the task. Then there is the pid namespace that will be used for children that pid namespace is stored in task->nsproxy->pid_ns. Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
367 lines
8.4 KiB
C
367 lines
8.4 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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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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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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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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/* 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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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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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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};
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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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