projects/linux·blob v5.6-rc6 · refs

680 lines · 16.3 KiB

1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Generic pidhash and scalable, time-bounded PID allocator
4 *
5 * (C) 2002-2003 Nadia Yvette Chambers, IBM
6 * (C) 2004 Nadia Yvette Chambers, Oracle
7 * (C) 2002-2004 Ingo Molnar, Red Hat
8 *
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.
12 *
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.
16 *
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).
22 *
23 * Pid namespaces:
24 * (C) 2007 Pavel Emelyanov <[email protected]>, OpenVZ, SWsoft Inc.
25 * (C) 2007 Sukadev Bhattiprolu <[email protected]>, IBM
26 * Many thanks to Oleg Nesterov for comments and help
27 *
28 */
29
30#include <linux/mm.h>
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>
45
46struct pid init_struct_pid = {
47 .count = REFCOUNT_INIT(1),
48 .tasks = {
49 { .first = NULL },
50 { .first = NULL },
51 { .first = NULL },
52 },
53 .level = 0,
54 .numbers = { {
55 .nr = 0,
56 .ns = &init_pid_ns,
57 }, }
58};
59
60int pid_max = PID_MAX_DEFAULT;
61
62#define RESERVED_PIDS 300
63
64int pid_max_min = RESERVED_PIDS + 1;
65int pid_max_max = PID_MAX_LIMIT;
66
67/*
68 * PID-map pages start out as NULL, they get allocated upon
69 * first use and are never deallocated. This way a low pid_max
70 * value does not cause lots of bitmaps to be allocated, but
71 * the scheme scales to up to 4 million PIDs, runtime.
72 */
73struct pid_namespace init_pid_ns = {
74 .kref = KREF_INIT(2),
75 .idr = IDR_INIT(init_pid_ns.idr),
76 .pid_allocated = PIDNS_ADDING,
77 .level = 0,
78 .child_reaper = &init_task,
79 .user_ns = &init_user_ns,
80 .ns.inum = PROC_PID_INIT_INO,
81#ifdef CONFIG_PID_NS
82 .ns.ops = &pidns_operations,
83#endif
84};
85EXPORT_SYMBOL_GPL(init_pid_ns);
86
87/*
88 * Note: disable interrupts while the pidmap_lock is held as an
89 * interrupt might come in and do read_lock(&tasklist_lock).
90 *
91 * If we don't disable interrupts there is a nasty deadlock between
92 * detach_pid()->free_pid() and another cpu that does
93 * spin_lock(&pidmap_lock) followed by an interrupt routine that does
94 * read_lock(&tasklist_lock);
95 *
96 * After we clean up the tasklist_lock and know there are no
97 * irq handlers that take it we can leave the interrupts enabled.
98 * For now it is easier to be safe than to prove it can't happen.
99 */
100
101static __cacheline_aligned_in_smp DEFINE_SPINLOCK(pidmap_lock);
102
103void put_pid(struct pid *pid)
104{
105 struct pid_namespace *ns;
106
107 if (!pid)
108 return;
109
110 ns = pid->numbers[pid->level].ns;
111 if (refcount_dec_and_test(&pid->count)) {
112 kmem_cache_free(ns->pid_cachep, pid);
113 put_pid_ns(ns);
114 }
115}
116EXPORT_SYMBOL_GPL(put_pid);
117
118static void delayed_put_pid(struct rcu_head *rhp)
119{
120 struct pid *pid = container_of(rhp, struct pid, rcu);
121 put_pid(pid);
122}
123
124void free_pid(struct pid *pid)
125{
126 /* We can be called with write_lock_irq(&tasklist_lock) held */
127 int i;
128 unsigned long flags;
129
130 spin_lock_irqsave(&pidmap_lock, flags);
131 for (i = 0; i <= pid->level; i++) {
132 struct upid *upid = pid->numbers + i;
133 struct pid_namespace *ns = upid->ns;
134 switch (--ns->pid_allocated) {
135 case 2:
136 case 1:
137 /* When all that is left in the pid namespace
138 * is the reaper wake up the reaper. The reaper
139 * may be sleeping in zap_pid_ns_processes().
140 */
141 wake_up_process(ns->child_reaper);
142 break;
143 case PIDNS_ADDING:
144 /* Handle a fork failure of the first process */
145 WARN_ON(ns->child_reaper);
146 ns->pid_allocated = 0;
147 /* fall through */
148 case 0:
149 schedule_work(&ns->proc_work);
150 break;
151 }
152
153 idr_remove(&ns->idr, upid->nr);
154 }
155 spin_unlock_irqrestore(&pidmap_lock, flags);
156
157 call_rcu(&pid->rcu, delayed_put_pid);
158}
159
160struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
161 size_t set_tid_size)
162{
163 struct pid *pid;
164 enum pid_type type;
165 int i, nr;
166 struct pid_namespace *tmp;
167 struct upid *upid;
168 int retval = -ENOMEM;
169
170 /*
171 * set_tid_size contains the size of the set_tid array. Starting at
172 * the most nested currently active PID namespace it tells alloc_pid()
173 * which PID to set for a process in that most nested PID namespace
174 * up to set_tid_size PID namespaces. It does not have to set the PID
175 * for a process in all nested PID namespaces but set_tid_size must
176 * never be greater than the current ns->level + 1.
177 */
178 if (set_tid_size > ns->level + 1)
179 return ERR_PTR(-EINVAL);
180
181 pid = kmem_cache_alloc(ns->pid_cachep, GFP_KERNEL);
182 if (!pid)
183 return ERR_PTR(retval);
184
185 tmp = ns;
186 pid->level = ns->level;
187
188 for (i = ns->level; i >= 0; i--) {
189 int tid = 0;
190
191 if (set_tid_size) {
192 tid = set_tid[ns->level - i];
193
194 retval = -EINVAL;
195 if (tid < 1 || tid >= pid_max)
196 goto out_free;
197 /*
198 * Also fail if a PID != 1 is requested and
199 * no PID 1 exists.
200 */
201 if (tid != 1 && !tmp->child_reaper)
202 goto out_free;
203 retval = -EPERM;
204 if (!ns_capable(tmp->user_ns, CAP_SYS_ADMIN))
205 goto out_free;
206 set_tid_size--;
207 }
208
209 idr_preload(GFP_KERNEL);
210 spin_lock_irq(&pidmap_lock);
211
212 if (tid) {
213 nr = idr_alloc(&tmp->idr, NULL, tid,
214 tid + 1, GFP_ATOMIC);
215 /*
216 * If ENOSPC is returned it means that the PID is
217 * alreay in use. Return EEXIST in that case.
218 */
219 if (nr == -ENOSPC)
220 nr = -EEXIST;
221 } else {
222 int pid_min = 1;
223 /*
224 * init really needs pid 1, but after reaching the
225 * maximum wrap back to RESERVED_PIDS
226 */
227 if (idr_get_cursor(&tmp->idr) > RESERVED_PIDS)
228 pid_min = RESERVED_PIDS;
229
230 /*
231 * Store a null pointer so find_pid_ns does not find
232 * a partially initialized PID (see below).
233 */
234 nr = idr_alloc_cyclic(&tmp->idr, NULL, pid_min,
235 pid_max, GFP_ATOMIC);
236 }
237 spin_unlock_irq(&pidmap_lock);
238 idr_preload_end();
239
240 if (nr < 0) {
241 retval = (nr == -ENOSPC) ? -EAGAIN : nr;
242 goto out_free;
243 }
244
245 pid->numbers[i].nr = nr;
246 pid->numbers[i].ns = tmp;
247 tmp = tmp->parent;
248 }
249
250 /*
251 * ENOMEM is not the most obvious choice especially for the case
252 * where the child subreaper has already exited and the pid
253 * namespace denies the creation of any new processes. But ENOMEM
254 * is what we have exposed to userspace for a long time and it is
255 * documented behavior for pid namespaces. So we can't easily
256 * change it even if there were an error code better suited.
257 */
258 retval = -ENOMEM;
259
260 if (unlikely(is_child_reaper(pid))) {
261 if (pid_ns_prepare_proc(ns))
262 goto out_free;
263 }
264
265 get_pid_ns(ns);
266 refcount_set(&pid->count, 1);
267 for (type = 0; type < PIDTYPE_MAX; ++type)
268 INIT_HLIST_HEAD(&pid->tasks[type]);
269
270 init_waitqueue_head(&pid->wait_pidfd);
271
272 upid = pid->numbers + ns->level;
273 spin_lock_irq(&pidmap_lock);
274 if (!(ns->pid_allocated & PIDNS_ADDING))
275 goto out_unlock;
276 for ( ; upid >= pid->numbers; --upid) {
277 /* Make the PID visible to find_pid_ns. */
278 idr_replace(&upid->ns->idr, pid, upid->nr);
279 upid->ns->pid_allocated++;
280 }
281 spin_unlock_irq(&pidmap_lock);
282
283 return pid;
284
285out_unlock:
286 spin_unlock_irq(&pidmap_lock);
287 put_pid_ns(ns);
288
289out_free:
290 spin_lock_irq(&pidmap_lock);
291 while (++i <= ns->level) {
292 upid = pid->numbers + i;
293 idr_remove(&upid->ns->idr, upid->nr);
294 }
295
296 /* On failure to allocate the first pid, reset the state */
297 if (ns->pid_allocated == PIDNS_ADDING)
298 idr_set_cursor(&ns->idr, 0);
299
300 spin_unlock_irq(&pidmap_lock);
301
302 kmem_cache_free(ns->pid_cachep, pid);
303 return ERR_PTR(retval);
304}
305
306void disable_pid_allocation(struct pid_namespace *ns)
307{
308 spin_lock_irq(&pidmap_lock);
309 ns->pid_allocated &= ~PIDNS_ADDING;
310 spin_unlock_irq(&pidmap_lock);
311}
312
313struct pid *find_pid_ns(int nr, struct pid_namespace *ns)
314{
315 return idr_find(&ns->idr, nr);
316}
317EXPORT_SYMBOL_GPL(find_pid_ns);
318
319struct pid *find_vpid(int nr)
320{
321 return find_pid_ns(nr, task_active_pid_ns(current));
322}
323EXPORT_SYMBOL_GPL(find_vpid);
324
325static struct pid **task_pid_ptr(struct task_struct *task, enum pid_type type)
326{
327 return (type == PIDTYPE_PID) ?
328 &task->thread_pid :
329 &task->signal->pids[type];
330}
331
332/*
333 * attach_pid() must be called with the tasklist_lock write-held.
334 */
335void attach_pid(struct task_struct *task, enum pid_type type)
336{
337 struct pid *pid = *task_pid_ptr(task, type);
338 hlist_add_head_rcu(&task->pid_links[type], &pid->tasks[type]);
339}
340
341static void __change_pid(struct task_struct *task, enum pid_type type,
342 struct pid *new)
343{
344 struct pid **pid_ptr = task_pid_ptr(task, type);
345 struct pid *pid;
346 int tmp;
347
348 pid = *pid_ptr;
349
350 hlist_del_rcu(&task->pid_links[type]);
351 *pid_ptr = new;
352
353 for (tmp = PIDTYPE_MAX; --tmp >= 0; )
354 if (pid_has_task(pid, tmp))
355 return;
356
357 free_pid(pid);
358}
359
360void detach_pid(struct task_struct *task, enum pid_type type)
361{
362 __change_pid(task, type, NULL);
363}
364
365void change_pid(struct task_struct *task, enum pid_type type,
366 struct pid *pid)
367{
368 __change_pid(task, type, pid);
369 attach_pid(task, type);
370}
371
372/* transfer_pid is an optimization of attach_pid(new), detach_pid(old) */
373void transfer_pid(struct task_struct *old, struct task_struct *new,
374 enum pid_type type)
375{
376 if (type == PIDTYPE_PID)
377 new->thread_pid = old->thread_pid;
378 hlist_replace_rcu(&old->pid_links[type], &new->pid_links[type]);
379}
380
381struct task_struct *pid_task(struct pid *pid, enum pid_type type)
382{
383 struct task_struct *result = NULL;
384 if (pid) {
385 struct hlist_node *first;
386 first = rcu_dereference_check(hlist_first_rcu(&pid->tasks[type]),
387 lockdep_tasklist_lock_is_held());
388 if (first)
389 result = hlist_entry(first, struct task_struct, pid_links[(type)]);
390 }
391 return result;
392}
393EXPORT_SYMBOL(pid_task);
394
395/*
396 * Must be called under rcu_read_lock().
397 */
398struct task_struct *find_task_by_pid_ns(pid_t nr, struct pid_namespace *ns)
399{
400 RCU_LOCKDEP_WARN(!rcu_read_lock_held(),
401 "find_task_by_pid_ns() needs rcu_read_lock() protection");
402 return pid_task(find_pid_ns(nr, ns), PIDTYPE_PID);
403}
404
405struct task_struct *find_task_by_vpid(pid_t vnr)
406{
407 return find_task_by_pid_ns(vnr, task_active_pid_ns(current));
408}
409
410struct task_struct *find_get_task_by_vpid(pid_t nr)
411{
412 struct task_struct *task;
413
414 rcu_read_lock();
415 task = find_task_by_vpid(nr);
416 if (task)
417 get_task_struct(task);
418 rcu_read_unlock();
419
420 return task;
421}
422
423struct pid *get_task_pid(struct task_struct *task, enum pid_type type)
424{
425 struct pid *pid;
426 rcu_read_lock();
427 pid = get_pid(rcu_dereference(*task_pid_ptr(task, type)));
428 rcu_read_unlock();
429 return pid;
430}
431EXPORT_SYMBOL_GPL(get_task_pid);
432
433struct task_struct *get_pid_task(struct pid *pid, enum pid_type type)
434{
435 struct task_struct *result;
436 rcu_read_lock();
437 result = pid_task(pid, type);
438 if (result)
439 get_task_struct(result);
440 rcu_read_unlock();
441 return result;
442}
443EXPORT_SYMBOL_GPL(get_pid_task);
444
445struct pid *find_get_pid(pid_t nr)
446{
447 struct pid *pid;
448
449 rcu_read_lock();
450 pid = get_pid(find_vpid(nr));
451 rcu_read_unlock();
452
453 return pid;
454}
455EXPORT_SYMBOL_GPL(find_get_pid);
456
457pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns)
458{
459 struct upid *upid;
460 pid_t nr = 0;
461
462 if (pid && ns->level <= pid->level) {
463 upid = &pid->numbers[ns->level];
464 if (upid->ns == ns)
465 nr = upid->nr;
466 }
467 return nr;
468}
469EXPORT_SYMBOL_GPL(pid_nr_ns);
470
471pid_t pid_vnr(struct pid *pid)
472{
473 return pid_nr_ns(pid, task_active_pid_ns(current));
474}
475EXPORT_SYMBOL_GPL(pid_vnr);
476
477pid_t __task_pid_nr_ns(struct task_struct *task, enum pid_type type,
478 struct pid_namespace *ns)
479{
480 pid_t nr = 0;
481
482 rcu_read_lock();
483 if (!ns)
484 ns = task_active_pid_ns(current);
485 if (likely(pid_alive(task)))
486 nr = pid_nr_ns(rcu_dereference(*task_pid_ptr(task, type)), ns);
487 rcu_read_unlock();
488
489 return nr;
490}
491EXPORT_SYMBOL(__task_pid_nr_ns);
492
493struct pid_namespace *task_active_pid_ns(struct task_struct *tsk)
494{
495 return ns_of_pid(task_pid(tsk));
496}
497EXPORT_SYMBOL_GPL(task_active_pid_ns);
498
499/*
500 * Used by proc to find the first pid that is greater than or equal to nr.
501 *
502 * If there is a pid at nr this function is exactly the same as find_pid_ns.
503 */
504struct pid *find_ge_pid(int nr, struct pid_namespace *ns)
505{
506 return idr_get_next(&ns->idr, &nr);
507}
508
509/**
510 * pidfd_create() - Create a new pid file descriptor.
511 *
512 * @pid: struct pid that the pidfd will reference
513 *
514 * This creates a new pid file descriptor with the O_CLOEXEC flag set.
515 *
516 * Note, that this function can only be called after the fd table has
517 * been unshared to avoid leaking the pidfd to the new process.
518 *
519 * Return: On success, a cloexec pidfd is returned.
520 * On error, a negative errno number will be returned.
521 */
522static int pidfd_create(struct pid *pid)
523{
524 int fd;
525
526 fd = anon_inode_getfd("[pidfd]", &pidfd_fops, get_pid(pid),
527 O_RDWR | O_CLOEXEC);
528 if (fd < 0)
529 put_pid(pid);
530
531 return fd;
532}
533
534/**
535 * pidfd_open() - Open new pid file descriptor.
536 *
537 * @pid: pid for which to retrieve a pidfd
538 * @flags: flags to pass
539 *
540 * This creates a new pid file descriptor with the O_CLOEXEC flag set for
541 * the process identified by @pid. Currently, the process identified by
542 * @pid must be a thread-group leader. This restriction currently exists
543 * for all aspects of pidfds including pidfd creation (CLONE_PIDFD cannot
544 * be used with CLONE_THREAD) and pidfd polling (only supports thread group
545 * leaders).
546 *
547 * Return: On success, a cloexec pidfd is returned.
548 * On error, a negative errno number will be returned.
549 */
550SYSCALL_DEFINE2(pidfd_open, pid_t, pid, unsigned int, flags)
551{
552 int fd;
553 struct pid *p;
554
555 if (flags)
556 return -EINVAL;
557
558 if (pid <= 0)
559 return -EINVAL;
560
561 p = find_get_pid(pid);
562 if (!p)
563 return -ESRCH;
564
565 if (pid_has_task(p, PIDTYPE_TGID))
566 fd = pidfd_create(p);
567 else
568 fd = -EINVAL;
569
570 put_pid(p);
571 return fd;
572}
573
574void __init pid_idr_init(void)
575{
576 /* Verify no one has done anything silly: */
577 BUILD_BUG_ON(PID_MAX_LIMIT >= PIDNS_ADDING);
578
579 /* bump default and minimum pid_max based on number of cpus */
580 pid_max = min(pid_max_max, max_t(int, pid_max,
581 PIDS_PER_CPU_DEFAULT * num_possible_cpus()));
582 pid_max_min = max_t(int, pid_max_min,
583 PIDS_PER_CPU_MIN * num_possible_cpus());
584 pr_info("pid_max: default: %u minimum: %u\n", pid_max, pid_max_min);
585
586 idr_init(&init_pid_ns.idr);
587
588 init_pid_ns.pid_cachep = KMEM_CACHE(pid,
589 SLAB_HWCACHE_ALIGN | SLAB_PANIC | SLAB_ACCOUNT);
590}
591
592static struct file *__pidfd_fget(struct task_struct *task, int fd)
593{
594 struct file *file;
595 int ret;
596
597 ret = mutex_lock_killable(&task->signal->cred_guard_mutex);
598 if (ret)
599 return ERR_PTR(ret);
600
601 if (ptrace_may_access(task, PTRACE_MODE_ATTACH_REALCREDS))
602 file = fget_task(task, fd);
603 else
604 file = ERR_PTR(-EPERM);
605
606 mutex_unlock(&task->signal->cred_guard_mutex);
607
608 return file ?: ERR_PTR(-EBADF);
609}
610
611static int pidfd_getfd(struct pid *pid, int fd)
612{
613 struct task_struct *task;
614 struct file *file;
615 int ret;
616
617 task = get_pid_task(pid, PIDTYPE_PID);
618 if (!task)
619 return -ESRCH;
620
621 file = __pidfd_fget(task, fd);
622 put_task_struct(task);
623 if (IS_ERR(file))
624 return PTR_ERR(file);
625
626 ret = security_file_receive(file);
627 if (ret) {
628 fput(file);
629 return ret;
630 }
631
632 ret = get_unused_fd_flags(O_CLOEXEC);
633 if (ret < 0)
634 fput(file);
635 else
636 fd_install(ret, file);
637
638 return ret;
639}
640
641/**
642 * sys_pidfd_getfd() - Get a file descriptor from another process
643 *
644 * @pidfd: the pidfd file descriptor of the process
645 * @fd: the file descriptor number to get
646 * @flags: flags on how to get the fd (reserved)
647 *
648 * This syscall gets a copy of a file descriptor from another process
649 * based on the pidfd, and file descriptor number. It requires that
650 * the calling process has the ability to ptrace the process represented
651 * by the pidfd. The process which is having its file descriptor copied
652 * is otherwise unaffected.
653 *
654 * Return: On success, a cloexec file descriptor is returned.
655 * On error, a negative errno number will be returned.
656 */
657SYSCALL_DEFINE3(pidfd_getfd, int, pidfd, int, fd,
658 unsigned int, flags)
659{
660 struct pid *pid;
661 struct fd f;
662 int ret;
663
664 /* flags is currently unused - make sure it's unset */
665 if (flags)
666 return -EINVAL;
667
668 f = fdget(pidfd);
669 if (!f.file)
670 return -EBADF;
671
672 pid = pidfd_pid(f.file);
673 if (IS_ERR(pid))
674 ret = PTR_ERR(pid);
675 else
676 ret = pidfd_getfd(pid, fd);
677
678 fdput(f);
679 return ret;
680}