1/* SPDX-License-Identifier: GPL-2.0 */
2#ifndef _LINUX_PID_H
3#define _LINUX_PID_H
4
5#include <linux/pid_types.h>
6#include <linux/rculist.h>
7#include <linux/rcupdate.h>
8#include <linux/refcount.h>
9#include <linux/sched.h>
10#include <linux/wait.h>
11
12/*
13 * What is struct pid?
14 *
15 * A struct pid is the kernel's internal notion of a process identifier.
16 * It refers to individual tasks, process groups, and sessions.  While
17 * there are processes attached to it the struct pid lives in a hash
18 * table, so it and then the processes that it refers to can be found
19 * quickly from the numeric pid value.  The attached processes may be
20 * quickly accessed by following pointers from struct pid.
21 *
22 * Storing pid_t values in the kernel and referring to them later has a
23 * problem.  The process originally with that pid may have exited and the
24 * pid allocator wrapped, and another process could have come along
25 * and been assigned that pid.
26 *
27 * Referring to user space processes by holding a reference to struct
28 * task_struct has a problem.  When the user space process exits
29 * the now useless task_struct is still kept.  A task_struct plus a
30 * stack consumes around 10K of low kernel memory.  More precisely
31 * this is THREAD_SIZE + sizeof(struct task_struct).  By comparison
32 * a struct pid is about 64 bytes.
33 *
34 * Holding a reference to struct pid solves both of these problems.
35 * It is small so holding a reference does not consume a lot of
36 * resources, and since a new struct pid is allocated when the numeric pid
37 * value is reused (when pids wrap around) we don't mistakenly refer to new
38 * processes.
39 */
40
41
42/*
43 * struct upid is used to get the id of the struct pid, as it is
44 * seen in particular namespace. Later the struct pid is found with
45 * find_pid_ns() using the int nr and struct pid_namespace *ns.
46 */
47
48#define RESERVED_PIDS 300
49
50struct upid {
51	int nr;
52	struct pid_namespace *ns;
53};
54
55struct pid
56{
57	refcount_t count;
58	unsigned int level;
59	spinlock_t lock;
60	struct dentry *stashed;
61	u64 ino;
62	/* lists of tasks that use this pid */
63	struct hlist_head tasks[PIDTYPE_MAX];
64	struct hlist_head inodes;
65	/* wait queue for pidfd notifications */
66	wait_queue_head_t wait_pidfd;
67	struct rcu_head rcu;
68	struct upid numbers[];
69};
70
71extern struct pid init_struct_pid;
72
73struct file;
74
75struct pid *pidfd_pid(const struct file *file);
76struct pid *pidfd_get_pid(unsigned int fd, unsigned int *flags);
77struct task_struct *pidfd_get_task(int pidfd, unsigned int *flags);
78int pidfd_prepare(struct pid *pid, unsigned int flags, struct file **ret);
79void do_notify_pidfd(struct task_struct *task);
80
81static inline struct pid *get_pid(struct pid *pid)
82{
83	if (pid)
84		refcount_inc(&pid->count);
85	return pid;
86}
87
88extern void put_pid(struct pid *pid);
89extern struct task_struct *pid_task(struct pid *pid, enum pid_type);
90static inline bool pid_has_task(struct pid *pid, enum pid_type type)
91{
92	return !hlist_empty(&pid->tasks[type]);
93}
94extern struct task_struct *get_pid_task(struct pid *pid, enum pid_type);
95
96extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type);
97
98/*
99 * these helpers must be called with the tasklist_lock write-held.
100 */
101extern void attach_pid(struct task_struct *task, enum pid_type);
102extern void detach_pid(struct task_struct *task, enum pid_type);
103extern void change_pid(struct task_struct *task, enum pid_type,
104			struct pid *pid);
105extern void exchange_tids(struct task_struct *task, struct task_struct *old);
106extern void transfer_pid(struct task_struct *old, struct task_struct *new,
107			 enum pid_type);
108
109extern int pid_max;
110extern int pid_max_min, pid_max_max;
111
112/*
113 * look up a PID in the hash table. Must be called with the tasklist_lock
114 * or rcu_read_lock() held.
115 *
116 * find_pid_ns() finds the pid in the namespace specified
117 * find_vpid() finds the pid by its virtual id, i.e. in the current namespace
118 *
119 * see also find_task_by_vpid() set in include/linux/sched.h
120 */
121extern struct pid *find_pid_ns(int nr, struct pid_namespace *ns);
122extern struct pid *find_vpid(int nr);
123
124/*
125 * Lookup a PID in the hash table, and return with it's count elevated.
126 */
127extern struct pid *find_get_pid(int nr);
128extern struct pid *find_ge_pid(int nr, struct pid_namespace *);
129
130extern struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
131			     size_t set_tid_size);
132extern void free_pid(struct pid *pid);
133extern void disable_pid_allocation(struct pid_namespace *ns);
134
135/*
136 * ns_of_pid() returns the pid namespace in which the specified pid was
137 * allocated.
138 *
139 * NOTE:
140 * 	ns_of_pid() is expected to be called for a process (task) that has
141 * 	an attached 'struct pid' (see attach_pid(), detach_pid()) i.e @pid
142 * 	is expected to be non-NULL. If @pid is NULL, caller should handle
143 * 	the resulting NULL pid-ns.
144 */
145static inline struct pid_namespace *ns_of_pid(struct pid *pid)
146{
147	struct pid_namespace *ns = NULL;
148	if (pid)
149		ns = pid->numbers[pid->level].ns;
150	return ns;
151}
152
153/*
154 * is_child_reaper returns true if the pid is the init process
155 * of the current namespace. As this one could be checked before
156 * pid_ns->child_reaper is assigned in copy_process, we check
157 * with the pid number.
158 */
159static inline bool is_child_reaper(struct pid *pid)
160{
161	return pid->numbers[pid->level].nr == 1;
162}
163
164/*
165 * the helpers to get the pid's id seen from different namespaces
166 *
167 * pid_nr()    : global id, i.e. the id seen from the init namespace;
168 * pid_vnr()   : virtual id, i.e. the id seen from the pid namespace of
169 *               current.
170 * pid_nr_ns() : id seen from the ns specified.
171 *
172 * see also task_xid_nr() etc in include/linux/sched.h
173 */
174
175static inline pid_t pid_nr(struct pid *pid)
176{
177	pid_t nr = 0;
178	if (pid)
179		nr = pid->numbers[0].nr;
180	return nr;
181}
182
183pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns);
184pid_t pid_vnr(struct pid *pid);
185
186#define do_each_pid_task(pid, type, task)				\
187	do {								\
188		if ((pid) != NULL)					\
189			hlist_for_each_entry_rcu((task),		\
190				&(pid)->tasks[type], pid_links[type]) {
191
192			/*
193			 * Both old and new leaders may be attached to
194			 * the same pid in the middle of de_thread().
195			 */
196#define while_each_pid_task(pid, type, task)				\
197				if (type == PIDTYPE_PID)		\
198					break;				\
199			}						\
200	} while (0)
201
202#define do_each_pid_thread(pid, type, task)				\
203	do_each_pid_task(pid, type, task) {				\
204		struct task_struct *tg___ = task;			\
205		for_each_thread(tg___, task) {
206
207#define while_each_pid_thread(pid, type, task)				\
208		}							\
209		task = tg___;						\
210	} while_each_pid_task(pid, type, task)
211
212static inline struct pid *task_pid(struct task_struct *task)
213{
214	return task->thread_pid;
215}
216
217/*
218 * the helpers to get the task's different pids as they are seen
219 * from various namespaces
220 *
221 * task_xid_nr()     : global id, i.e. the id seen from the init namespace;
222 * task_xid_vnr()    : virtual id, i.e. the id seen from the pid namespace of
223 *                     current.
224 * task_xid_nr_ns()  : id seen from the ns specified;
225 *
226 * see also pid_nr() etc in include/linux/pid.h
227 */
228pid_t __task_pid_nr_ns(struct task_struct *task, enum pid_type type, struct pid_namespace *ns);
229
230static inline pid_t task_pid_nr(struct task_struct *tsk)
231{
232	return tsk->pid;
233}
234
235static inline pid_t task_pid_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)
236{
237	return __task_pid_nr_ns(tsk, PIDTYPE_PID, ns);
238}
239
240static inline pid_t task_pid_vnr(struct task_struct *tsk)
241{
242	return __task_pid_nr_ns(tsk, PIDTYPE_PID, NULL);
243}
244
245
246static inline pid_t task_tgid_nr(struct task_struct *tsk)
247{
248	return tsk->tgid;
249}
250
251/**
252 * pid_alive - check that a task structure is not stale
253 * @p: Task structure to be checked.
254 *
255 * Test if a process is not yet dead (at most zombie state)
256 * If pid_alive fails, then pointers within the task structure
257 * can be stale and must not be dereferenced.
258 *
259 * Return: 1 if the process is alive. 0 otherwise.
260 */
261static inline int pid_alive(const struct task_struct *p)
262{
263	return p->thread_pid != NULL;
264}
265
266static inline pid_t task_pgrp_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)
267{
268	return __task_pid_nr_ns(tsk, PIDTYPE_PGID, ns);
269}
270
271static inline pid_t task_pgrp_vnr(struct task_struct *tsk)
272{
273	return __task_pid_nr_ns(tsk, PIDTYPE_PGID, NULL);
274}
275
276
277static inline pid_t task_session_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)
278{
279	return __task_pid_nr_ns(tsk, PIDTYPE_SID, ns);
280}
281
282static inline pid_t task_session_vnr(struct task_struct *tsk)
283{
284	return __task_pid_nr_ns(tsk, PIDTYPE_SID, NULL);
285}
286
287static inline pid_t task_tgid_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)
288{
289	return __task_pid_nr_ns(tsk, PIDTYPE_TGID, ns);
290}
291
292static inline pid_t task_tgid_vnr(struct task_struct *tsk)
293{
294	return __task_pid_nr_ns(tsk, PIDTYPE_TGID, NULL);
295}
296
297static inline pid_t task_ppid_nr_ns(const struct task_struct *tsk, struct pid_namespace *ns)
298{
299	pid_t pid = 0;
300
301	rcu_read_lock();
302	if (pid_alive(tsk))
303		pid = task_tgid_nr_ns(rcu_dereference(tsk->real_parent), ns);
304	rcu_read_unlock();
305
306	return pid;
307}
308
309static inline pid_t task_ppid_nr(const struct task_struct *tsk)
310{
311	return task_ppid_nr_ns(tsk, &init_pid_ns);
312}
313
314/* Obsolete, do not use: */
315static inline pid_t task_pgrp_nr(struct task_struct *tsk)
316{
317	return task_pgrp_nr_ns(tsk, &init_pid_ns);
318}
319
320/**
321 * is_global_init - check if a task structure is init. Since init
322 * is free to have sub-threads we need to check tgid.
323 * @tsk: Task structure to be checked.
324 *
325 * Check if a task structure is the first user space task the kernel created.
326 *
327 * Return: 1 if the task structure is init. 0 otherwise.
328 */
329static inline int is_global_init(struct task_struct *tsk)
330{
331	return task_tgid_nr(tsk) == 1;
332}
333
334#endif /* _LINUX_PID_H */
335