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1/*
2 * Generic pidhash and scalable, time-bounded PID allocator
3 *
4 * (C) 2002-2003 Nadia Yvette Chambers, IBM
5 * (C) 2004 Nadia Yvette Chambers, Oracle
6 * (C) 2002-2004 Ingo Molnar, Red Hat
7 *
8 * pid-structures are backing objects for tasks sharing a given ID to chain
9 * against. There is very little to them aside from hashing them and
10 * parking tasks using given ID's on a list.
11 *
12 * The hash is always changed with the tasklist_lock write-acquired,
13 * and the hash is only accessed with the tasklist_lock at least
14 * read-acquired, so there's no additional SMP locking needed here.
15 *
16 * We have a list of bitmap pages, which bitmaps represent the PID space.
17 * Allocating and freeing PIDs is completely lockless. The worst-case
18 * allocation scenario when all but one out of 1 million PIDs possible are
19 * allocated already: the scanning of 32 list entries and at most PAGE_SIZE
20 * bytes. The typical fastpath is a single successful setbit. Freeing is O(1).
21 *
22 * Pid namespaces:
23 * (C) 2007 Pavel Emelyanov <xemul@openvz.org>, OpenVZ, SWsoft Inc.
24 * (C) 2007 Sukadev Bhattiprolu <sukadev@us.ibm.com>, IBM
25 * Many thanks to Oleg Nesterov for comments and help
26 *
27 */
28
29#include <linux/mm.h>
30#include <linux/export.h>
31#include <linux/slab.h>
32#include <linux/init.h>
33#include <linux/rculist.h>
34#include <linux/bootmem.h>
35#include <linux/hash.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/proc_fs.h>
41#include <linux/sched/task.h>
42#include <linux/idr.h>
43
44struct pid init_struct_pid = {
45 .count = ATOMIC_INIT(1),
46 .tasks = {
47 { .first = NULL },
48 { .first = NULL },
49 { .first = NULL },
50 },
51 .level = 0,
52 .numbers = { {
53 .nr = 0,
54 .ns = &init_pid_ns,
55 }, }
56};
57
58int pid_max = PID_MAX_DEFAULT;
59
60#define RESERVED_PIDS 300
61
62int pid_max_min = RESERVED_PIDS + 1;
63int pid_max_max = PID_MAX_LIMIT;
64
65/*
66 * PID-map pages start out as NULL, they get allocated upon
67 * first use and are never deallocated. This way a low pid_max
68 * value does not cause lots of bitmaps to be allocated, but
69 * the scheme scales to up to 4 million PIDs, runtime.
70 */
71struct pid_namespace init_pid_ns = {
72 .kref = KREF_INIT(2),
73 .idr = IDR_INIT(init_pid_ns.idr),
74 .pid_allocated = PIDNS_ADDING,
75 .level = 0,
76 .child_reaper = &init_task,
77 .user_ns = &init_user_ns,
78 .ns.inum = PROC_PID_INIT_INO,
79#ifdef CONFIG_PID_NS
80 .ns.ops = &pidns_operations,
81#endif
82};
83EXPORT_SYMBOL_GPL(init_pid_ns);
84
85/*
86 * Note: disable interrupts while the pidmap_lock is held as an
87 * interrupt might come in and do read_lock(&tasklist_lock).
88 *
89 * If we don't disable interrupts there is a nasty deadlock between
90 * detach_pid()->free_pid() and another cpu that does
91 * spin_lock(&pidmap_lock) followed by an interrupt routine that does
92 * read_lock(&tasklist_lock);
93 *
94 * After we clean up the tasklist_lock and know there are no
95 * irq handlers that take it we can leave the interrupts enabled.
96 * For now it is easier to be safe than to prove it can't happen.
97 */
98
99static __cacheline_aligned_in_smp DEFINE_SPINLOCK(pidmap_lock);
100
101void put_pid(struct pid *pid)
102{
103 struct pid_namespace *ns;
104
105 if (!pid)
106 return;
107
108 ns = pid->numbers[pid->level].ns;
109 if ((atomic_read(&pid->count) == 1) ||
110 atomic_dec_and_test(&pid->count)) {
111 kmem_cache_free(ns->pid_cachep, pid);
112 put_pid_ns(ns);
113 }
114}
115EXPORT_SYMBOL_GPL(put_pid);
116
117static void delayed_put_pid(struct rcu_head *rhp)
118{
119 struct pid *pid = container_of(rhp, struct pid, rcu);
120 put_pid(pid);
121}
122
123void free_pid(struct pid *pid)
124{
125 /* We can be called with write_lock_irq(&tasklist_lock) held */
126 int i;
127 unsigned long flags;
128
129 spin_lock_irqsave(&pidmap_lock, flags);
130 for (i = 0; i <= pid->level; i++) {
131 struct upid *upid = pid->numbers + i;
132 struct pid_namespace *ns = upid->ns;
133 switch (--ns->pid_allocated) {
134 case 2:
135 case 1:
136 /* When all that is left in the pid namespace
137 * is the reaper wake up the reaper. The reaper
138 * may be sleeping in zap_pid_ns_processes().
139 */
140 wake_up_process(ns->child_reaper);
141 break;
142 case PIDNS_ADDING:
143 /* Handle a fork failure of the first process */
144 WARN_ON(ns->child_reaper);
145 ns->pid_allocated = 0;
146 /* fall through */
147 case 0:
148 schedule_work(&ns->proc_work);
149 break;
150 }
151
152 idr_remove(&ns->idr, upid->nr);
153 }
154 spin_unlock_irqrestore(&pidmap_lock, flags);
155
156 call_rcu(&pid->rcu, delayed_put_pid);
157}
158
159struct pid *alloc_pid(struct pid_namespace *ns)
160{
161 struct pid *pid;
162 enum pid_type type;
163 int i, nr;
164 struct pid_namespace *tmp;
165 struct upid *upid;
166 int retval = -ENOMEM;
167
168 pid = kmem_cache_alloc(ns->pid_cachep, GFP_KERNEL);
169 if (!pid)
170 return ERR_PTR(retval);
171
172 tmp = ns;
173 pid->level = ns->level;
174
175 for (i = ns->level; i >= 0; i--) {
176 int pid_min = 1;
177
178 idr_preload(GFP_KERNEL);
179 spin_lock_irq(&pidmap_lock);
180
181 /*
182 * init really needs pid 1, but after reaching the maximum
183 * wrap back to RESERVED_PIDS
184 */
185 if (idr_get_cursor(&tmp->idr) > RESERVED_PIDS)
186 pid_min = RESERVED_PIDS;
187
188 /*
189 * Store a null pointer so find_pid_ns does not find
190 * a partially initialized PID (see below).
191 */
192 nr = idr_alloc_cyclic(&tmp->idr, NULL, pid_min,
193 pid_max, GFP_ATOMIC);
194 spin_unlock_irq(&pidmap_lock);
195 idr_preload_end();
196
197 if (nr < 0) {
198 retval = nr;
199 goto out_free;
200 }
201
202 pid->numbers[i].nr = nr;
203 pid->numbers[i].ns = tmp;
204 tmp = tmp->parent;
205 }
206
207 if (unlikely(is_child_reaper(pid))) {
208 if (pid_ns_prepare_proc(ns))
209 goto out_free;
210 }
211
212 get_pid_ns(ns);
213 atomic_set(&pid->count, 1);
214 for (type = 0; type < PIDTYPE_MAX; ++type)
215 INIT_HLIST_HEAD(&pid->tasks[type]);
216
217 upid = pid->numbers + ns->level;
218 spin_lock_irq(&pidmap_lock);
219 if (!(ns->pid_allocated & PIDNS_ADDING))
220 goto out_unlock;
221 for ( ; upid >= pid->numbers; --upid) {
222 /* Make the PID visible to find_pid_ns. */
223 idr_replace(&upid->ns->idr, pid, upid->nr);
224 upid->ns->pid_allocated++;
225 }
226 spin_unlock_irq(&pidmap_lock);
227
228 return pid;
229
230out_unlock:
231 spin_unlock_irq(&pidmap_lock);
232 put_pid_ns(ns);
233
234out_free:
235 spin_lock_irq(&pidmap_lock);
236 while (++i <= ns->level)
237 idr_remove(&ns->idr, (pid->numbers + i)->nr);
238
239 /* On failure to allocate the first pid, reset the state */
240 if (ns->pid_allocated == PIDNS_ADDING)
241 idr_set_cursor(&ns->idr, 0);
242
243 spin_unlock_irq(&pidmap_lock);
244
245 kmem_cache_free(ns->pid_cachep, pid);
246 return ERR_PTR(retval);
247}
248
249void disable_pid_allocation(struct pid_namespace *ns)
250{
251 spin_lock_irq(&pidmap_lock);
252 ns->pid_allocated &= ~PIDNS_ADDING;
253 spin_unlock_irq(&pidmap_lock);
254}
255
256struct pid *find_pid_ns(int nr, struct pid_namespace *ns)
257{
258 return idr_find(&ns->idr, nr);
259}
260EXPORT_SYMBOL_GPL(find_pid_ns);
261
262struct pid *find_vpid(int nr)
263{
264 return find_pid_ns(nr, task_active_pid_ns(current));
265}
266EXPORT_SYMBOL_GPL(find_vpid);
267
268/*
269 * attach_pid() must be called with the tasklist_lock write-held.
270 */
271void attach_pid(struct task_struct *task, enum pid_type type)
272{
273 struct pid_link *link = &task->pids[type];
274 hlist_add_head_rcu(&link->node, &link->pid->tasks[type]);
275}
276
277static void __change_pid(struct task_struct *task, enum pid_type type,
278 struct pid *new)
279{
280 struct pid_link *link;
281 struct pid *pid;
282 int tmp;
283
284 link = &task->pids[type];
285 pid = link->pid;
286
287 hlist_del_rcu(&link->node);
288 link->pid = new;
289
290 for (tmp = PIDTYPE_MAX; --tmp >= 0; )
291 if (!hlist_empty(&pid->tasks[tmp]))
292 return;
293
294 free_pid(pid);
295}
296
297void detach_pid(struct task_struct *task, enum pid_type type)
298{
299 __change_pid(task, type, NULL);
300}
301
302void change_pid(struct task_struct *task, enum pid_type type,
303 struct pid *pid)
304{
305 __change_pid(task, type, pid);
306 attach_pid(task, type);
307}
308
309/* transfer_pid is an optimization of attach_pid(new), detach_pid(old) */
310void transfer_pid(struct task_struct *old, struct task_struct *new,
311 enum pid_type type)
312{
313 new->pids[type].pid = old->pids[type].pid;
314 hlist_replace_rcu(&old->pids[type].node, &new->pids[type].node);
315}
316
317struct task_struct *pid_task(struct pid *pid, enum pid_type type)
318{
319 struct task_struct *result = NULL;
320 if (pid) {
321 struct hlist_node *first;
322 first = rcu_dereference_check(hlist_first_rcu(&pid->tasks[type]),
323 lockdep_tasklist_lock_is_held());
324 if (first)
325 result = hlist_entry(first, struct task_struct, pids[(type)].node);
326 }
327 return result;
328}
329EXPORT_SYMBOL(pid_task);
330
331/*
332 * Must be called under rcu_read_lock().
333 */
334struct task_struct *find_task_by_pid_ns(pid_t nr, struct pid_namespace *ns)
335{
336 RCU_LOCKDEP_WARN(!rcu_read_lock_held(),
337 "find_task_by_pid_ns() needs rcu_read_lock() protection");
338 return pid_task(find_pid_ns(nr, ns), PIDTYPE_PID);
339}
340
341struct task_struct *find_task_by_vpid(pid_t vnr)
342{
343 return find_task_by_pid_ns(vnr, task_active_pid_ns(current));
344}
345
346struct task_struct *find_get_task_by_vpid(pid_t nr)
347{
348 struct task_struct *task;
349
350 rcu_read_lock();
351 task = find_task_by_vpid(nr);
352 if (task)
353 get_task_struct(task);
354 rcu_read_unlock();
355
356 return task;
357}
358
359struct pid *get_task_pid(struct task_struct *task, enum pid_type type)
360{
361 struct pid *pid;
362 rcu_read_lock();
363 if (type != PIDTYPE_PID)
364 task = task->group_leader;
365 pid = get_pid(rcu_dereference(task->pids[type].pid));
366 rcu_read_unlock();
367 return pid;
368}
369EXPORT_SYMBOL_GPL(get_task_pid);
370
371struct task_struct *get_pid_task(struct pid *pid, enum pid_type type)
372{
373 struct task_struct *result;
374 rcu_read_lock();
375 result = pid_task(pid, type);
376 if (result)
377 get_task_struct(result);
378 rcu_read_unlock();
379 return result;
380}
381EXPORT_SYMBOL_GPL(get_pid_task);
382
383struct pid *find_get_pid(pid_t nr)
384{
385 struct pid *pid;
386
387 rcu_read_lock();
388 pid = get_pid(find_vpid(nr));
389 rcu_read_unlock();
390
391 return pid;
392}
393EXPORT_SYMBOL_GPL(find_get_pid);
394
395pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns)
396{
397 struct upid *upid;
398 pid_t nr = 0;
399
400 if (pid && ns->level <= pid->level) {
401 upid = &pid->numbers[ns->level];
402 if (upid->ns == ns)
403 nr = upid->nr;
404 }
405 return nr;
406}
407EXPORT_SYMBOL_GPL(pid_nr_ns);
408
409pid_t pid_vnr(struct pid *pid)
410{
411 return pid_nr_ns(pid, task_active_pid_ns(current));
412}
413EXPORT_SYMBOL_GPL(pid_vnr);
414
415pid_t __task_pid_nr_ns(struct task_struct *task, enum pid_type type,
416 struct pid_namespace *ns)
417{
418 pid_t nr = 0;
419
420 rcu_read_lock();
421 if (!ns)
422 ns = task_active_pid_ns(current);
423 if (likely(pid_alive(task))) {
424 if (type != PIDTYPE_PID) {
425 if (type == __PIDTYPE_TGID)
426 type = PIDTYPE_PID;
427
428 task = task->group_leader;
429 }
430 nr = pid_nr_ns(rcu_dereference(task->pids[type].pid), ns);
431 }
432 rcu_read_unlock();
433
434 return nr;
435}
436EXPORT_SYMBOL(__task_pid_nr_ns);
437
438struct pid_namespace *task_active_pid_ns(struct task_struct *tsk)
439{
440 return ns_of_pid(task_pid(tsk));
441}
442EXPORT_SYMBOL_GPL(task_active_pid_ns);
443
444/*
445 * Used by proc to find the first pid that is greater than or equal to nr.
446 *
447 * If there is a pid at nr this function is exactly the same as find_pid_ns.
448 */
449struct pid *find_ge_pid(int nr, struct pid_namespace *ns)
450{
451 return idr_get_next(&ns->idr, &nr);
452}
453
454void __init pid_idr_init(void)
455{
456 /* Verify no one has done anything silly: */
457 BUILD_BUG_ON(PID_MAX_LIMIT >= PIDNS_ADDING);
458
459 /* bump default and minimum pid_max based on number of cpus */
460 pid_max = min(pid_max_max, max_t(int, pid_max,
461 PIDS_PER_CPU_DEFAULT * num_possible_cpus()));
462 pid_max_min = max_t(int, pid_max_min,
463 PIDS_PER_CPU_MIN * num_possible_cpus());
464 pr_info("pid_max: default: %u minimum: %u\n", pid_max, pid_max_min);
465
466 idr_init(&init_pid_ns.idr);
467
468 init_pid_ns.pid_cachep = KMEM_CACHE(pid,
469 SLAB_HWCACHE_ALIGN | SLAB_PANIC | SLAB_ACCOUNT);
470}
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 <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
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#include <net/sock.h>
46#include <uapi/linux/pidfd.h>
47
48struct pid init_struct_pid = {
49 .count = REFCOUNT_INIT(1),
50 .tasks = {
51 { .first = NULL },
52 { .first = NULL },
53 { .first = NULL },
54 },
55 .level = 0,
56 .numbers = { {
57 .nr = 0,
58 .ns = &init_pid_ns,
59 }, }
60};
61
62int pid_max = PID_MAX_DEFAULT;
63
64#define RESERVED_PIDS 300
65
66int pid_max_min = RESERVED_PIDS + 1;
67int pid_max_max = PID_MAX_LIMIT;
68
69/*
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.
74 */
75struct pid_namespace init_pid_ns = {
76 .ns.count = REFCOUNT_INIT(2),
77 .idr = IDR_INIT(init_pid_ns.idr),
78 .pid_allocated = PIDNS_ADDING,
79 .level = 0,
80 .child_reaper = &init_task,
81 .user_ns = &init_user_ns,
82 .ns.inum = PROC_PID_INIT_INO,
83#ifdef CONFIG_PID_NS
84 .ns.ops = &pidns_operations,
85#endif
86#if defined(CONFIG_SYSCTL) && defined(CONFIG_MEMFD_CREATE)
87 .memfd_noexec_scope = MEMFD_NOEXEC_SCOPE_EXEC,
88#endif
89};
90EXPORT_SYMBOL_GPL(init_pid_ns);
91
92/*
93 * Note: disable interrupts while the pidmap_lock is held as an
94 * interrupt might come in and do read_lock(&tasklist_lock).
95 *
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);
100 *
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.
104 */
105
106static __cacheline_aligned_in_smp DEFINE_SPINLOCK(pidmap_lock);
107
108void put_pid(struct pid *pid)
109{
110 struct pid_namespace *ns;
111
112 if (!pid)
113 return;
114
115 ns = pid->numbers[pid->level].ns;
116 if (refcount_dec_and_test(&pid->count)) {
117 kmem_cache_free(ns->pid_cachep, pid);
118 put_pid_ns(ns);
119 }
120}
121EXPORT_SYMBOL_GPL(put_pid);
122
123static void delayed_put_pid(struct rcu_head *rhp)
124{
125 struct pid *pid = container_of(rhp, struct pid, rcu);
126 put_pid(pid);
127}
128
129void free_pid(struct pid *pid)
130{
131 /* We can be called with write_lock_irq(&tasklist_lock) held */
132 int i;
133 unsigned long flags;
134
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) {
140 case 2:
141 case 1:
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().
145 */
146 wake_up_process(ns->child_reaper);
147 break;
148 case PIDNS_ADDING:
149 /* Handle a fork failure of the first process */
150 WARN_ON(ns->child_reaper);
151 ns->pid_allocated = 0;
152 break;
153 }
154
155 idr_remove(&ns->idr, upid->nr);
156 }
157 spin_unlock_irqrestore(&pidmap_lock, flags);
158
159 call_rcu(&pid->rcu, delayed_put_pid);
160}
161
162struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
163 size_t set_tid_size)
164{
165 struct pid *pid;
166 enum pid_type type;
167 int i, nr;
168 struct pid_namespace *tmp;
169 struct upid *upid;
170 int retval = -ENOMEM;
171
172 /*
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.
179 */
180 if (set_tid_size > ns->level + 1)
181 return ERR_PTR(-EINVAL);
182
183 pid = kmem_cache_alloc(ns->pid_cachep, GFP_KERNEL);
184 if (!pid)
185 return ERR_PTR(retval);
186
187 tmp = ns;
188 pid->level = ns->level;
189
190 for (i = ns->level; i >= 0; i--) {
191 int tid = 0;
192
193 if (set_tid_size) {
194 tid = set_tid[ns->level - i];
195
196 retval = -EINVAL;
197 if (tid < 1 || tid >= pid_max)
198 goto out_free;
199 /*
200 * Also fail if a PID != 1 is requested and
201 * no PID 1 exists.
202 */
203 if (tid != 1 && !tmp->child_reaper)
204 goto out_free;
205 retval = -EPERM;
206 if (!checkpoint_restore_ns_capable(tmp->user_ns))
207 goto out_free;
208 set_tid_size--;
209 }
210
211 idr_preload(GFP_KERNEL);
212 spin_lock_irq(&pidmap_lock);
213
214 if (tid) {
215 nr = idr_alloc(&tmp->idr, NULL, tid,
216 tid + 1, GFP_ATOMIC);
217 /*
218 * If ENOSPC is returned it means that the PID is
219 * alreay in use. Return EEXIST in that case.
220 */
221 if (nr == -ENOSPC)
222 nr = -EEXIST;
223 } else {
224 int pid_min = 1;
225 /*
226 * init really needs pid 1, but after reaching the
227 * maximum wrap back to RESERVED_PIDS
228 */
229 if (idr_get_cursor(&tmp->idr) > RESERVED_PIDS)
230 pid_min = RESERVED_PIDS;
231
232 /*
233 * Store a null pointer so find_pid_ns does not find
234 * a partially initialized PID (see below).
235 */
236 nr = idr_alloc_cyclic(&tmp->idr, NULL, pid_min,
237 pid_max, GFP_ATOMIC);
238 }
239 spin_unlock_irq(&pidmap_lock);
240 idr_preload_end();
241
242 if (nr < 0) {
243 retval = (nr == -ENOSPC) ? -EAGAIN : nr;
244 goto out_free;
245 }
246
247 pid->numbers[i].nr = nr;
248 pid->numbers[i].ns = tmp;
249 tmp = tmp->parent;
250 }
251
252 /*
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.
259 */
260 retval = -ENOMEM;
261
262 get_pid_ns(ns);
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]);
267
268 init_waitqueue_head(&pid->wait_pidfd);
269 INIT_HLIST_HEAD(&pid->inodes);
270
271 upid = pid->numbers + ns->level;
272 spin_lock_irq(&pidmap_lock);
273 if (!(ns->pid_allocated & PIDNS_ADDING))
274 goto out_unlock;
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++;
279 }
280 spin_unlock_irq(&pidmap_lock);
281
282 return pid;
283
284out_unlock:
285 spin_unlock_irq(&pidmap_lock);
286 put_pid_ns(ns);
287
288out_free:
289 spin_lock_irq(&pidmap_lock);
290 while (++i <= ns->level) {
291 upid = pid->numbers + i;
292 idr_remove(&upid->ns->idr, upid->nr);
293 }
294
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);
298
299 spin_unlock_irq(&pidmap_lock);
300
301 kmem_cache_free(ns->pid_cachep, pid);
302 return ERR_PTR(retval);
303}
304
305void disable_pid_allocation(struct pid_namespace *ns)
306{
307 spin_lock_irq(&pidmap_lock);
308 ns->pid_allocated &= ~PIDNS_ADDING;
309 spin_unlock_irq(&pidmap_lock);
310}
311
312struct pid *find_pid_ns(int nr, struct pid_namespace *ns)
313{
314 return idr_find(&ns->idr, nr);
315}
316EXPORT_SYMBOL_GPL(find_pid_ns);
317
318struct pid *find_vpid(int nr)
319{
320 return find_pid_ns(nr, task_active_pid_ns(current));
321}
322EXPORT_SYMBOL_GPL(find_vpid);
323
324static struct pid **task_pid_ptr(struct task_struct *task, enum pid_type type)
325{
326 return (type == PIDTYPE_PID) ?
327 &task->thread_pid :
328 &task->signal->pids[type];
329}
330
331/*
332 * attach_pid() must be called with the tasklist_lock write-held.
333 */
334void attach_pid(struct task_struct *task, enum pid_type type)
335{
336 struct pid *pid = *task_pid_ptr(task, type);
337 hlist_add_head_rcu(&task->pid_links[type], &pid->tasks[type]);
338}
339
340static void __change_pid(struct task_struct *task, enum pid_type type,
341 struct pid *new)
342{
343 struct pid **pid_ptr = task_pid_ptr(task, type);
344 struct pid *pid;
345 int tmp;
346
347 pid = *pid_ptr;
348
349 hlist_del_rcu(&task->pid_links[type]);
350 *pid_ptr = new;
351
352 for (tmp = PIDTYPE_MAX; --tmp >= 0; )
353 if (pid_has_task(pid, tmp))
354 return;
355
356 free_pid(pid);
357}
358
359void detach_pid(struct task_struct *task, enum pid_type type)
360{
361 __change_pid(task, type, NULL);
362}
363
364void change_pid(struct task_struct *task, enum pid_type type,
365 struct pid *pid)
366{
367 __change_pid(task, type, pid);
368 attach_pid(task, type);
369}
370
371void exchange_tids(struct task_struct *left, struct task_struct *right)
372{
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];
377
378 /* Swap the single entry tid lists */
379 hlists_swap_heads_rcu(head1, head2);
380
381 /* Swap the per task_struct pid */
382 rcu_assign_pointer(left->thread_pid, pid2);
383 rcu_assign_pointer(right->thread_pid, pid1);
384
385 /* Swap the cached value */
386 WRITE_ONCE(left->pid, pid_nr(pid2));
387 WRITE_ONCE(right->pid, pid_nr(pid1));
388}
389
390/* transfer_pid is an optimization of attach_pid(new), detach_pid(old) */
391void transfer_pid(struct task_struct *old, struct task_struct *new,
392 enum pid_type type)
393{
394 if (type == PIDTYPE_PID)
395 new->thread_pid = old->thread_pid;
396 hlist_replace_rcu(&old->pid_links[type], &new->pid_links[type]);
397}
398
399struct task_struct *pid_task(struct pid *pid, enum pid_type type)
400{
401 struct task_struct *result = NULL;
402 if (pid) {
403 struct hlist_node *first;
404 first = rcu_dereference_check(hlist_first_rcu(&pid->tasks[type]),
405 lockdep_tasklist_lock_is_held());
406 if (first)
407 result = hlist_entry(first, struct task_struct, pid_links[(type)]);
408 }
409 return result;
410}
411EXPORT_SYMBOL(pid_task);
412
413/*
414 * Must be called under rcu_read_lock().
415 */
416struct task_struct *find_task_by_pid_ns(pid_t nr, struct pid_namespace *ns)
417{
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);
421}
422
423struct task_struct *find_task_by_vpid(pid_t vnr)
424{
425 return find_task_by_pid_ns(vnr, task_active_pid_ns(current));
426}
427
428struct task_struct *find_get_task_by_vpid(pid_t nr)
429{
430 struct task_struct *task;
431
432 rcu_read_lock();
433 task = find_task_by_vpid(nr);
434 if (task)
435 get_task_struct(task);
436 rcu_read_unlock();
437
438 return task;
439}
440
441struct pid *get_task_pid(struct task_struct *task, enum pid_type type)
442{
443 struct pid *pid;
444 rcu_read_lock();
445 pid = get_pid(rcu_dereference(*task_pid_ptr(task, type)));
446 rcu_read_unlock();
447 return pid;
448}
449EXPORT_SYMBOL_GPL(get_task_pid);
450
451struct task_struct *get_pid_task(struct pid *pid, enum pid_type type)
452{
453 struct task_struct *result;
454 rcu_read_lock();
455 result = pid_task(pid, type);
456 if (result)
457 get_task_struct(result);
458 rcu_read_unlock();
459 return result;
460}
461EXPORT_SYMBOL_GPL(get_pid_task);
462
463struct pid *find_get_pid(pid_t nr)
464{
465 struct pid *pid;
466
467 rcu_read_lock();
468 pid = get_pid(find_vpid(nr));
469 rcu_read_unlock();
470
471 return pid;
472}
473EXPORT_SYMBOL_GPL(find_get_pid);
474
475pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns)
476{
477 struct upid *upid;
478 pid_t nr = 0;
479
480 if (pid && ns->level <= pid->level) {
481 upid = &pid->numbers[ns->level];
482 if (upid->ns == ns)
483 nr = upid->nr;
484 }
485 return nr;
486}
487EXPORT_SYMBOL_GPL(pid_nr_ns);
488
489pid_t pid_vnr(struct pid *pid)
490{
491 return pid_nr_ns(pid, task_active_pid_ns(current));
492}
493EXPORT_SYMBOL_GPL(pid_vnr);
494
495pid_t __task_pid_nr_ns(struct task_struct *task, enum pid_type type,
496 struct pid_namespace *ns)
497{
498 pid_t nr = 0;
499
500 rcu_read_lock();
501 if (!ns)
502 ns = task_active_pid_ns(current);
503 nr = pid_nr_ns(rcu_dereference(*task_pid_ptr(task, type)), ns);
504 rcu_read_unlock();
505
506 return nr;
507}
508EXPORT_SYMBOL(__task_pid_nr_ns);
509
510struct pid_namespace *task_active_pid_ns(struct task_struct *tsk)
511{
512 return ns_of_pid(task_pid(tsk));
513}
514EXPORT_SYMBOL_GPL(task_active_pid_ns);
515
516/*
517 * Used by proc to find the first pid that is greater than or equal to nr.
518 *
519 * If there is a pid at nr this function is exactly the same as find_pid_ns.
520 */
521struct pid *find_ge_pid(int nr, struct pid_namespace *ns)
522{
523 return idr_get_next(&ns->idr, &nr);
524}
525EXPORT_SYMBOL_GPL(find_ge_pid);
526
527struct pid *pidfd_get_pid(unsigned int fd, unsigned int *flags)
528{
529 struct fd f;
530 struct pid *pid;
531
532 f = fdget(fd);
533 if (!f.file)
534 return ERR_PTR(-EBADF);
535
536 pid = pidfd_pid(f.file);
537 if (!IS_ERR(pid)) {
538 get_pid(pid);
539 *flags = f.file->f_flags;
540 }
541
542 fdput(f);
543 return pid;
544}
545
546/**
547 * pidfd_get_task() - Get the task associated with a pidfd
548 *
549 * @pidfd: pidfd for which to get the task
550 * @flags: flags associated with this pidfd
551 *
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.
554 *
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).
559 *
560 * Return: On success, the task_struct associated with the pidfd.
561 * On error, a negative errno number will be returned.
562 */
563struct task_struct *pidfd_get_task(int pidfd, unsigned int *flags)
564{
565 unsigned int f_flags;
566 struct pid *pid;
567 struct task_struct *task;
568
569 pid = pidfd_get_pid(pidfd, &f_flags);
570 if (IS_ERR(pid))
571 return ERR_CAST(pid);
572
573 task = get_pid_task(pid, PIDTYPE_TGID);
574 put_pid(pid);
575 if (!task)
576 return ERR_PTR(-ESRCH);
577
578 *flags = f_flags;
579 return task;
580}
581
582/**
583 * pidfd_create() - Create a new pid file descriptor.
584 *
585 * @pid: struct pid that the pidfd will reference
586 * @flags: flags to pass
587 *
588 * This creates a new pid file descriptor with the O_CLOEXEC flag set.
589 *
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.
592 *
593 * This symbol should not be explicitly exported to loadable modules.
594 *
595 * Return: On success, a cloexec pidfd is returned.
596 * On error, a negative errno number will be returned.
597 */
598int pidfd_create(struct pid *pid, unsigned int flags)
599{
600 int pidfd;
601 struct file *pidfd_file;
602
603 pidfd = pidfd_prepare(pid, flags, &pidfd_file);
604 if (pidfd < 0)
605 return pidfd;
606
607 fd_install(pidfd, pidfd_file);
608 return pidfd;
609}
610
611/**
612 * sys_pidfd_open() - Open new pid file descriptor.
613 *
614 * @pid: pid for which to retrieve a pidfd
615 * @flags: flags to pass
616 *
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
622 * leaders).
623 *
624 * Return: On success, a cloexec pidfd is returned.
625 * On error, a negative errno number will be returned.
626 */
627SYSCALL_DEFINE2(pidfd_open, pid_t, pid, unsigned int, flags)
628{
629 int fd;
630 struct pid *p;
631
632 if (flags & ~PIDFD_NONBLOCK)
633 return -EINVAL;
634
635 if (pid <= 0)
636 return -EINVAL;
637
638 p = find_get_pid(pid);
639 if (!p)
640 return -ESRCH;
641
642 fd = pidfd_create(p, flags);
643
644 put_pid(p);
645 return fd;
646}
647
648void __init pid_idr_init(void)
649{
650 /* Verify no one has done anything silly: */
651 BUILD_BUG_ON(PID_MAX_LIMIT >= PIDNS_ADDING);
652
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);
659
660 idr_init(&init_pid_ns.idr);
661
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,
666 NULL);
667}
668
669static struct file *__pidfd_fget(struct task_struct *task, int fd)
670{
671 struct file *file;
672 int ret;
673
674 ret = down_read_killable(&task->signal->exec_update_lock);
675 if (ret)
676 return ERR_PTR(ret);
677
678 if (ptrace_may_access(task, PTRACE_MODE_ATTACH_REALCREDS))
679 file = fget_task(task, fd);
680 else
681 file = ERR_PTR(-EPERM);
682
683 up_read(&task->signal->exec_update_lock);
684
685 return file ?: ERR_PTR(-EBADF);
686}
687
688static int pidfd_getfd(struct pid *pid, int fd)
689{
690 struct task_struct *task;
691 struct file *file;
692 int ret;
693
694 task = get_pid_task(pid, PIDTYPE_PID);
695 if (!task)
696 return -ESRCH;
697
698 file = __pidfd_fget(task, fd);
699 put_task_struct(task);
700 if (IS_ERR(file))
701 return PTR_ERR(file);
702
703 ret = receive_fd(file, NULL, O_CLOEXEC);
704 fput(file);
705
706 return ret;
707}
708
709/**
710 * sys_pidfd_getfd() - Get a file descriptor from another process
711 *
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)
715 *
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.
721 *
722 * Return: On success, a cloexec file descriptor is returned.
723 * On error, a negative errno number will be returned.
724 */
725SYSCALL_DEFINE3(pidfd_getfd, int, pidfd, int, fd,
726 unsigned int, flags)
727{
728 struct pid *pid;
729 struct fd f;
730 int ret;
731
732 /* flags is currently unused - make sure it's unset */
733 if (flags)
734 return -EINVAL;
735
736 f = fdget(pidfd);
737 if (!f.file)
738 return -EBADF;
739
740 pid = pidfd_pid(f.file);
741 if (IS_ERR(pid))
742 ret = PTR_ERR(pid);
743 else
744 ret = pidfd_getfd(pid, fd);
745
746 fdput(f);
747 return ret;
748}