1 // SPDX-License-Identifier: GPL-2.0-only
3 * Generic pidhash and scalable, time-bounded PID allocator
5 * (C) 2002-2003 Nadia Yvette Chambers, IBM
6 * (C) 2004 Nadia Yvette Chambers, Oracle
7 * (C) 2002-2004 Ingo Molnar, Red Hat
9 * pid-structures are backing objects for tasks sharing a given ID to chain
10 * against. There is very little to them aside from hashing them and
11 * parking tasks using given ID's on a list.
13 * The hash is always changed with the tasklist_lock write-acquired,
14 * and the hash is only accessed with the tasklist_lock at least
15 * read-acquired, so there's no additional SMP locking needed here.
17 * We have a list of bitmap pages, which bitmaps represent the PID space.
18 * Allocating and freeing PIDs is completely lockless. The worst-case
19 * allocation scenario when all but one out of 1 million PIDs possible are
20 * allocated already: the scanning of 32 list entries and at most PAGE_SIZE
21 * bytes. The typical fastpath is a single successful setbit. Freeing is O(1).
24 * (C) 2007 Pavel Emelyanov <xemul@openvz.org>, OpenVZ, SWsoft Inc.
25 * (C) 2007 Sukadev Bhattiprolu <sukadev@us.ibm.com>, IBM
26 * Many thanks to Oleg Nesterov for comments and help
31 #include <linux/export.h>
32 #include <linux/slab.h>
33 #include <linux/init.h>
34 #include <linux/rculist.h>
35 #include <linux/memblock.h>
36 #include <linux/pid_namespace.h>
37 #include <linux/init_task.h>
38 #include <linux/syscalls.h>
39 #include <linux/proc_ns.h>
40 #include <linux/refcount.h>
41 #include <linux/anon_inodes.h>
42 #include <linux/sched/signal.h>
43 #include <linux/sched/task.h>
44 #include <linux/idr.h>
46 #include <uapi/linux/pidfd.h>
48 struct pid init_struct_pid = {
49 .count = REFCOUNT_INIT(1),
62 int pid_max = PID_MAX_DEFAULT;
64 #define RESERVED_PIDS 300
66 int pid_max_min = RESERVED_PIDS + 1;
67 int pid_max_max = PID_MAX_LIMIT;
70 * PID-map pages start out as NULL, they get allocated upon
71 * first use and are never deallocated. This way a low pid_max
72 * value does not cause lots of bitmaps to be allocated, but
73 * the scheme scales to up to 4 million PIDs, runtime.
75 struct pid_namespace init_pid_ns = {
76 .ns.count = REFCOUNT_INIT(2),
77 .idr = IDR_INIT(init_pid_ns.idr),
78 .pid_allocated = PIDNS_ADDING,
80 .child_reaper = &init_task,
81 .user_ns = &init_user_ns,
82 .ns.inum = PROC_PID_INIT_INO,
84 .ns.ops = &pidns_operations,
86 #if defined(CONFIG_SYSCTL) && defined(CONFIG_MEMFD_CREATE)
87 .memfd_noexec_scope = MEMFD_NOEXEC_SCOPE_EXEC,
90 EXPORT_SYMBOL_GPL(init_pid_ns);
93 * Note: disable interrupts while the pidmap_lock is held as an
94 * interrupt might come in and do read_lock(&tasklist_lock).
96 * If we don't disable interrupts there is a nasty deadlock between
97 * detach_pid()->free_pid() and another cpu that does
98 * spin_lock(&pidmap_lock) followed by an interrupt routine that does
99 * read_lock(&tasklist_lock);
101 * After we clean up the tasklist_lock and know there are no
102 * irq handlers that take it we can leave the interrupts enabled.
103 * For now it is easier to be safe than to prove it can't happen.
106 static __cacheline_aligned_in_smp DEFINE_SPINLOCK(pidmap_lock);
108 void put_pid(struct pid *pid)
110 struct pid_namespace *ns;
115 ns = pid->numbers[pid->level].ns;
116 if (refcount_dec_and_test(&pid->count)) {
117 kmem_cache_free(ns->pid_cachep, pid);
121 EXPORT_SYMBOL_GPL(put_pid);
123 static void delayed_put_pid(struct rcu_head *rhp)
125 struct pid *pid = container_of(rhp, struct pid, rcu);
129 void free_pid(struct pid *pid)
131 /* We can be called with write_lock_irq(&tasklist_lock) held */
135 spin_lock_irqsave(&pidmap_lock, flags);
136 for (i = 0; i <= pid->level; i++) {
137 struct upid *upid = pid->numbers + i;
138 struct pid_namespace *ns = upid->ns;
139 switch (--ns->pid_allocated) {
142 /* When all that is left in the pid namespace
143 * is the reaper wake up the reaper. The reaper
144 * may be sleeping in zap_pid_ns_processes().
146 wake_up_process(ns->child_reaper);
149 /* Handle a fork failure of the first process */
150 WARN_ON(ns->child_reaper);
151 ns->pid_allocated = 0;
155 idr_remove(&ns->idr, upid->nr);
157 spin_unlock_irqrestore(&pidmap_lock, flags);
159 call_rcu(&pid->rcu, delayed_put_pid);
162 struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
168 struct pid_namespace *tmp;
170 int retval = -ENOMEM;
173 * set_tid_size contains the size of the set_tid array. Starting at
174 * the most nested currently active PID namespace it tells alloc_pid()
175 * which PID to set for a process in that most nested PID namespace
176 * up to set_tid_size PID namespaces. It does not have to set the PID
177 * for a process in all nested PID namespaces but set_tid_size must
178 * never be greater than the current ns->level + 1.
180 if (set_tid_size > ns->level + 1)
181 return ERR_PTR(-EINVAL);
183 pid = kmem_cache_alloc(ns->pid_cachep, GFP_KERNEL);
185 return ERR_PTR(retval);
188 pid->level = ns->level;
190 for (i = ns->level; i >= 0; i--) {
194 tid = set_tid[ns->level - i];
197 if (tid < 1 || tid >= pid_max)
200 * Also fail if a PID != 1 is requested and
203 if (tid != 1 && !tmp->child_reaper)
206 if (!checkpoint_restore_ns_capable(tmp->user_ns))
211 idr_preload(GFP_KERNEL);
212 spin_lock_irq(&pidmap_lock);
215 nr = idr_alloc(&tmp->idr, NULL, tid,
216 tid + 1, GFP_ATOMIC);
218 * If ENOSPC is returned it means that the PID is
219 * alreay in use. Return EEXIST in that case.
226 * init really needs pid 1, but after reaching the
227 * maximum wrap back to RESERVED_PIDS
229 if (idr_get_cursor(&tmp->idr) > RESERVED_PIDS)
230 pid_min = RESERVED_PIDS;
233 * Store a null pointer so find_pid_ns does not find
234 * a partially initialized PID (see below).
236 nr = idr_alloc_cyclic(&tmp->idr, NULL, pid_min,
237 pid_max, GFP_ATOMIC);
239 spin_unlock_irq(&pidmap_lock);
243 retval = (nr == -ENOSPC) ? -EAGAIN : nr;
247 pid->numbers[i].nr = nr;
248 pid->numbers[i].ns = tmp;
253 * ENOMEM is not the most obvious choice especially for the case
254 * where the child subreaper has already exited and the pid
255 * namespace denies the creation of any new processes. But ENOMEM
256 * is what we have exposed to userspace for a long time and it is
257 * documented behavior for pid namespaces. So we can't easily
258 * change it even if there were an error code better suited.
263 refcount_set(&pid->count, 1);
264 spin_lock_init(&pid->lock);
265 for (type = 0; type < PIDTYPE_MAX; ++type)
266 INIT_HLIST_HEAD(&pid->tasks[type]);
268 init_waitqueue_head(&pid->wait_pidfd);
269 INIT_HLIST_HEAD(&pid->inodes);
271 upid = pid->numbers + ns->level;
272 spin_lock_irq(&pidmap_lock);
273 if (!(ns->pid_allocated & PIDNS_ADDING))
275 for ( ; upid >= pid->numbers; --upid) {
276 /* Make the PID visible to find_pid_ns. */
277 idr_replace(&upid->ns->idr, pid, upid->nr);
278 upid->ns->pid_allocated++;
280 spin_unlock_irq(&pidmap_lock);
285 spin_unlock_irq(&pidmap_lock);
289 spin_lock_irq(&pidmap_lock);
290 while (++i <= ns->level) {
291 upid = pid->numbers + i;
292 idr_remove(&upid->ns->idr, upid->nr);
295 /* On failure to allocate the first pid, reset the state */
296 if (ns->pid_allocated == PIDNS_ADDING)
297 idr_set_cursor(&ns->idr, 0);
299 spin_unlock_irq(&pidmap_lock);
301 kmem_cache_free(ns->pid_cachep, pid);
302 return ERR_PTR(retval);
305 void disable_pid_allocation(struct pid_namespace *ns)
307 spin_lock_irq(&pidmap_lock);
308 ns->pid_allocated &= ~PIDNS_ADDING;
309 spin_unlock_irq(&pidmap_lock);
312 struct pid *find_pid_ns(int nr, struct pid_namespace *ns)
314 return idr_find(&ns->idr, nr);
316 EXPORT_SYMBOL_GPL(find_pid_ns);
318 struct pid *find_vpid(int nr)
320 return find_pid_ns(nr, task_active_pid_ns(current));
322 EXPORT_SYMBOL_GPL(find_vpid);
324 static struct pid **task_pid_ptr(struct task_struct *task, enum pid_type type)
326 return (type == PIDTYPE_PID) ?
328 &task->signal->pids[type];
332 * attach_pid() must be called with the tasklist_lock write-held.
334 void attach_pid(struct task_struct *task, enum pid_type type)
336 struct pid *pid = *task_pid_ptr(task, type);
337 hlist_add_head_rcu(&task->pid_links[type], &pid->tasks[type]);
340 static void __change_pid(struct task_struct *task, enum pid_type type,
343 struct pid **pid_ptr = task_pid_ptr(task, type);
349 hlist_del_rcu(&task->pid_links[type]);
352 for (tmp = PIDTYPE_MAX; --tmp >= 0; )
353 if (pid_has_task(pid, tmp))
359 void detach_pid(struct task_struct *task, enum pid_type type)
361 __change_pid(task, type, NULL);
364 void change_pid(struct task_struct *task, enum pid_type type,
367 __change_pid(task, type, pid);
368 attach_pid(task, type);
371 void exchange_tids(struct task_struct *left, struct task_struct *right)
373 struct pid *pid1 = left->thread_pid;
374 struct pid *pid2 = right->thread_pid;
375 struct hlist_head *head1 = &pid1->tasks[PIDTYPE_PID];
376 struct hlist_head *head2 = &pid2->tasks[PIDTYPE_PID];
378 /* Swap the single entry tid lists */
379 hlists_swap_heads_rcu(head1, head2);
381 /* Swap the per task_struct pid */
382 rcu_assign_pointer(left->thread_pid, pid2);
383 rcu_assign_pointer(right->thread_pid, pid1);
385 /* Swap the cached value */
386 WRITE_ONCE(left->pid, pid_nr(pid2));
387 WRITE_ONCE(right->pid, pid_nr(pid1));
390 /* transfer_pid is an optimization of attach_pid(new), detach_pid(old) */
391 void transfer_pid(struct task_struct *old, struct task_struct *new,
394 if (type == PIDTYPE_PID)
395 new->thread_pid = old->thread_pid;
396 hlist_replace_rcu(&old->pid_links[type], &new->pid_links[type]);
399 struct task_struct *pid_task(struct pid *pid, enum pid_type type)
401 struct task_struct *result = NULL;
403 struct hlist_node *first;
404 first = rcu_dereference_check(hlist_first_rcu(&pid->tasks[type]),
405 lockdep_tasklist_lock_is_held());
407 result = hlist_entry(first, struct task_struct, pid_links[(type)]);
411 EXPORT_SYMBOL(pid_task);
414 * Must be called under rcu_read_lock().
416 struct task_struct *find_task_by_pid_ns(pid_t nr, struct pid_namespace *ns)
418 RCU_LOCKDEP_WARN(!rcu_read_lock_held(),
419 "find_task_by_pid_ns() needs rcu_read_lock() protection");
420 return pid_task(find_pid_ns(nr, ns), PIDTYPE_PID);
423 struct task_struct *find_task_by_vpid(pid_t vnr)
425 return find_task_by_pid_ns(vnr, task_active_pid_ns(current));
428 struct task_struct *find_get_task_by_vpid(pid_t nr)
430 struct task_struct *task;
433 task = find_task_by_vpid(nr);
435 get_task_struct(task);
441 struct pid *get_task_pid(struct task_struct *task, enum pid_type type)
445 pid = get_pid(rcu_dereference(*task_pid_ptr(task, type)));
449 EXPORT_SYMBOL_GPL(get_task_pid);
451 struct task_struct *get_pid_task(struct pid *pid, enum pid_type type)
453 struct task_struct *result;
455 result = pid_task(pid, type);
457 get_task_struct(result);
461 EXPORT_SYMBOL_GPL(get_pid_task);
463 struct pid *find_get_pid(pid_t nr)
468 pid = get_pid(find_vpid(nr));
473 EXPORT_SYMBOL_GPL(find_get_pid);
475 pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns)
480 if (pid && ns->level <= pid->level) {
481 upid = &pid->numbers[ns->level];
487 EXPORT_SYMBOL_GPL(pid_nr_ns);
489 pid_t pid_vnr(struct pid *pid)
491 return pid_nr_ns(pid, task_active_pid_ns(current));
493 EXPORT_SYMBOL_GPL(pid_vnr);
495 pid_t __task_pid_nr_ns(struct task_struct *task, enum pid_type type,
496 struct pid_namespace *ns)
502 ns = task_active_pid_ns(current);
503 nr = pid_nr_ns(rcu_dereference(*task_pid_ptr(task, type)), ns);
508 EXPORT_SYMBOL(__task_pid_nr_ns);
510 struct pid_namespace *task_active_pid_ns(struct task_struct *tsk)
512 return ns_of_pid(task_pid(tsk));
514 EXPORT_SYMBOL_GPL(task_active_pid_ns);
517 * Used by proc to find the first pid that is greater than or equal to nr.
519 * If there is a pid at nr this function is exactly the same as find_pid_ns.
521 struct pid *find_ge_pid(int nr, struct pid_namespace *ns)
523 return idr_get_next(&ns->idr, &nr);
525 EXPORT_SYMBOL_GPL(find_ge_pid);
527 struct pid *pidfd_get_pid(unsigned int fd, unsigned int *flags)
534 return ERR_PTR(-EBADF);
536 pid = pidfd_pid(f.file);
539 *flags = f.file->f_flags;
547 * pidfd_get_task() - Get the task associated with a pidfd
549 * @pidfd: pidfd for which to get the task
550 * @flags: flags associated with this pidfd
552 * Return the task associated with @pidfd. The function takes a reference on
553 * the returned task. The caller is responsible for releasing that reference.
555 * Currently, the process identified by @pidfd is always a thread-group leader.
556 * This restriction currently exists for all aspects of pidfds including pidfd
557 * creation (CLONE_PIDFD cannot be used with CLONE_THREAD) and pidfd polling
558 * (only supports thread group leaders).
560 * Return: On success, the task_struct associated with the pidfd.
561 * On error, a negative errno number will be returned.
563 struct task_struct *pidfd_get_task(int pidfd, unsigned int *flags)
565 unsigned int f_flags;
567 struct task_struct *task;
569 pid = pidfd_get_pid(pidfd, &f_flags);
571 return ERR_CAST(pid);
573 task = get_pid_task(pid, PIDTYPE_TGID);
576 return ERR_PTR(-ESRCH);
583 * pidfd_create() - Create a new pid file descriptor.
585 * @pid: struct pid that the pidfd will reference
586 * @flags: flags to pass
588 * This creates a new pid file descriptor with the O_CLOEXEC flag set.
590 * Note, that this function can only be called after the fd table has
591 * been unshared to avoid leaking the pidfd to the new process.
593 * This symbol should not be explicitly exported to loadable modules.
595 * Return: On success, a cloexec pidfd is returned.
596 * On error, a negative errno number will be returned.
598 int pidfd_create(struct pid *pid, unsigned int flags)
601 struct file *pidfd_file;
603 pidfd = pidfd_prepare(pid, flags, &pidfd_file);
607 fd_install(pidfd, pidfd_file);
612 * sys_pidfd_open() - Open new pid file descriptor.
614 * @pid: pid for which to retrieve a pidfd
615 * @flags: flags to pass
617 * This creates a new pid file descriptor with the O_CLOEXEC flag set for
618 * the process identified by @pid. Currently, the process identified by
619 * @pid must be a thread-group leader. This restriction currently exists
620 * for all aspects of pidfds including pidfd creation (CLONE_PIDFD cannot
621 * be used with CLONE_THREAD) and pidfd polling (only supports thread group
624 * Return: On success, a cloexec pidfd is returned.
625 * On error, a negative errno number will be returned.
627 SYSCALL_DEFINE2(pidfd_open, pid_t, pid, unsigned int, flags)
632 if (flags & ~PIDFD_NONBLOCK)
638 p = find_get_pid(pid);
642 fd = pidfd_create(p, flags);
648 void __init pid_idr_init(void)
650 /* Verify no one has done anything silly: */
651 BUILD_BUG_ON(PID_MAX_LIMIT >= PIDNS_ADDING);
653 /* bump default and minimum pid_max based on number of cpus */
654 pid_max = min(pid_max_max, max_t(int, pid_max,
655 PIDS_PER_CPU_DEFAULT * num_possible_cpus()));
656 pid_max_min = max_t(int, pid_max_min,
657 PIDS_PER_CPU_MIN * num_possible_cpus());
658 pr_info("pid_max: default: %u minimum: %u\n", pid_max, pid_max_min);
660 idr_init(&init_pid_ns.idr);
662 init_pid_ns.pid_cachep = kmem_cache_create("pid",
663 struct_size_t(struct pid, numbers, 1),
664 __alignof__(struct pid),
665 SLAB_HWCACHE_ALIGN | SLAB_PANIC | SLAB_ACCOUNT,
669 static struct file *__pidfd_fget(struct task_struct *task, int fd)
674 ret = down_read_killable(&task->signal->exec_update_lock);
678 if (ptrace_may_access(task, PTRACE_MODE_ATTACH_REALCREDS))
679 file = fget_task(task, fd);
681 file = ERR_PTR(-EPERM);
683 up_read(&task->signal->exec_update_lock);
685 return file ?: ERR_PTR(-EBADF);
688 static int pidfd_getfd(struct pid *pid, int fd)
690 struct task_struct *task;
694 task = get_pid_task(pid, PIDTYPE_PID);
698 file = __pidfd_fget(task, fd);
699 put_task_struct(task);
701 return PTR_ERR(file);
703 ret = receive_fd(file, O_CLOEXEC);
710 * sys_pidfd_getfd() - Get a file descriptor from another process
712 * @pidfd: the pidfd file descriptor of the process
713 * @fd: the file descriptor number to get
714 * @flags: flags on how to get the fd (reserved)
716 * This syscall gets a copy of a file descriptor from another process
717 * based on the pidfd, and file descriptor number. It requires that
718 * the calling process has the ability to ptrace the process represented
719 * by the pidfd. The process which is having its file descriptor copied
720 * is otherwise unaffected.
722 * Return: On success, a cloexec file descriptor is returned.
723 * On error, a negative errno number will be returned.
725 SYSCALL_DEFINE3(pidfd_getfd, int, pidfd, int, fd,
732 /* flags is currently unused - make sure it's unset */
740 pid = pidfd_pid(f.file);
744 ret = pidfd_getfd(pid, fd);