1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef _LINUX_PID_H
3 #define _LINUX_PID_H
4 
5 #include <linux/rculist.h>
6 #include <linux/wait.h>
7 #include <linux/refcount.h>
8 
9 enum pid_type
10 {
11 	PIDTYPE_PID,
12 	PIDTYPE_TGID,
13 	PIDTYPE_PGID,
14 	PIDTYPE_SID,
15 	PIDTYPE_MAX,
16 };
17 
18 /*
19  * What is struct pid?
20  *
21  * A struct pid is the kernel's internal notion of a process identifier.
22  * It refers to individual tasks, process groups, and sessions.  While
23  * there are processes attached to it the struct pid lives in a hash
24  * table, so it and then the processes that it refers to can be found
25  * quickly from the numeric pid value.  The attached processes may be
26  * quickly accessed by following pointers from struct pid.
27  *
28  * Storing pid_t values in the kernel and referring to them later has a
29  * problem.  The process originally with that pid may have exited and the
30  * pid allocator wrapped, and another process could have come along
31  * and been assigned that pid.
32  *
33  * Referring to user space processes by holding a reference to struct
34  * task_struct has a problem.  When the user space process exits
35  * the now useless task_struct is still kept.  A task_struct plus a
36  * stack consumes around 10K of low kernel memory.  More precisely
37  * this is THREAD_SIZE + sizeof(struct task_struct).  By comparison
38  * a struct pid is about 64 bytes.
39  *
40  * Holding a reference to struct pid solves both of these problems.
41  * It is small so holding a reference does not consume a lot of
42  * resources, and since a new struct pid is allocated when the numeric pid
43  * value is reused (when pids wrap around) we don't mistakenly refer to new
44  * processes.
45  */
46 
47 
48 /*
49  * struct upid is used to get the id of the struct pid, as it is
50  * seen in particular namespace. Later the struct pid is found with
51  * find_pid_ns() using the int nr and struct pid_namespace *ns.
52  */
53 
54 struct upid {
55 	int nr;
56 	struct pid_namespace *ns;
57 };
58 
59 struct pid
60 {
61 	refcount_t count;
62 	unsigned int level;
63 	spinlock_t lock;
64 	/* lists of tasks that use this pid */
65 	struct hlist_head tasks[PIDTYPE_MAX];
66 	struct hlist_head inodes;
67 	/* wait queue for pidfd notifications */
68 	wait_queue_head_t wait_pidfd;
69 	struct rcu_head rcu;
70 	struct upid numbers[1];
71 };
72 
73 extern struct pid init_struct_pid;
74 
75 extern const struct file_operations pidfd_fops;
76 
77 struct file;
78 
79 extern struct pid *pidfd_pid(const struct file *file);
80 struct pid *pidfd_get_pid(unsigned int fd, unsigned int *flags);
81 struct task_struct *pidfd_get_task(int pidfd, unsigned int *flags);
82 int pidfd_create(struct pid *pid, unsigned int flags);
83 
get_pid(struct pid * pid)84 static inline struct pid *get_pid(struct pid *pid)
85 {
86 	if (pid)
87 		refcount_inc(&pid->count);
88 	return pid;
89 }
90 
91 extern void put_pid(struct pid *pid);
92 extern struct task_struct *pid_task(struct pid *pid, enum pid_type);
pid_has_task(struct pid * pid,enum pid_type type)93 static inline bool pid_has_task(struct pid *pid, enum pid_type type)
94 {
95 	return !hlist_empty(&pid->tasks[type]);
96 }
97 extern struct task_struct *get_pid_task(struct pid *pid, enum pid_type);
98 
99 extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type);
100 
101 /*
102  * these helpers must be called with the tasklist_lock write-held.
103  */
104 extern void attach_pid(struct task_struct *task, enum pid_type);
105 extern void detach_pid(struct task_struct *task, enum pid_type);
106 extern void change_pid(struct task_struct *task, enum pid_type,
107 			struct pid *pid);
108 extern void exchange_tids(struct task_struct *task, struct task_struct *old);
109 extern void transfer_pid(struct task_struct *old, struct task_struct *new,
110 			 enum pid_type);
111 
112 struct pid_namespace;
113 extern struct pid_namespace init_pid_ns;
114 
115 extern int pid_max;
116 extern int pid_max_min, pid_max_max;
117 
118 /*
119  * look up a PID in the hash table. Must be called with the tasklist_lock
120  * or rcu_read_lock() held.
121  *
122  * find_pid_ns() finds the pid in the namespace specified
123  * find_vpid() finds the pid by its virtual id, i.e. in the current namespace
124  *
125  * see also find_task_by_vpid() set in include/linux/sched.h
126  */
127 extern struct pid *find_pid_ns(int nr, struct pid_namespace *ns);
128 extern struct pid *find_vpid(int nr);
129 
130 /*
131  * Lookup a PID in the hash table, and return with it's count elevated.
132  */
133 extern struct pid *find_get_pid(int nr);
134 extern struct pid *find_ge_pid(int nr, struct pid_namespace *);
135 
136 extern struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
137 			     size_t set_tid_size);
138 extern void free_pid(struct pid *pid);
139 extern void disable_pid_allocation(struct pid_namespace *ns);
140 
141 /*
142  * ns_of_pid() returns the pid namespace in which the specified pid was
143  * allocated.
144  *
145  * NOTE:
146  * 	ns_of_pid() is expected to be called for a process (task) that has
147  * 	an attached 'struct pid' (see attach_pid(), detach_pid()) i.e @pid
148  * 	is expected to be non-NULL. If @pid is NULL, caller should handle
149  * 	the resulting NULL pid-ns.
150  */
ns_of_pid(struct pid * pid)151 static inline struct pid_namespace *ns_of_pid(struct pid *pid)
152 {
153 	struct pid_namespace *ns = NULL;
154 	if (pid)
155 		ns = pid->numbers[pid->level].ns;
156 	return ns;
157 }
158 
159 /*
160  * is_child_reaper returns true if the pid is the init process
161  * of the current namespace. As this one could be checked before
162  * pid_ns->child_reaper is assigned in copy_process, we check
163  * with the pid number.
164  */
is_child_reaper(struct pid * pid)165 static inline bool is_child_reaper(struct pid *pid)
166 {
167 	return pid->numbers[pid->level].nr == 1;
168 }
169 
170 /*
171  * the helpers to get the pid's id seen from different namespaces
172  *
173  * pid_nr()    : global id, i.e. the id seen from the init namespace;
174  * pid_vnr()   : virtual id, i.e. the id seen from the pid namespace of
175  *               current.
176  * pid_nr_ns() : id seen from the ns specified.
177  *
178  * see also task_xid_nr() etc in include/linux/sched.h
179  */
180 
pid_nr(struct pid * pid)181 static inline pid_t pid_nr(struct pid *pid)
182 {
183 	pid_t nr = 0;
184 	if (pid)
185 		nr = pid->numbers[0].nr;
186 	return nr;
187 }
188 
189 pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns);
190 pid_t pid_vnr(struct pid *pid);
191 
192 #define do_each_pid_task(pid, type, task)				\
193 	do {								\
194 		if ((pid) != NULL)					\
195 			hlist_for_each_entry_rcu((task),		\
196 				&(pid)->tasks[type], pid_links[type]) {
197 
198 			/*
199 			 * Both old and new leaders may be attached to
200 			 * the same pid in the middle of de_thread().
201 			 */
202 #define while_each_pid_task(pid, type, task)				\
203 				if (type == PIDTYPE_PID)		\
204 					break;				\
205 			}						\
206 	} while (0)
207 
208 #define do_each_pid_thread(pid, type, task)				\
209 	do_each_pid_task(pid, type, task) {				\
210 		struct task_struct *tg___ = task;			\
211 		for_each_thread(tg___, task) {
212 
213 #define while_each_pid_thread(pid, type, task)				\
214 		}							\
215 		task = tg___;						\
216 	} while_each_pid_task(pid, type, task)
217 #endif /* _LINUX_PID_H */
218