1 // SPDX-License-Identifier: GPL-2.0
3 * Copyright (C) 1991, 1992 Linus Torvalds
6 #include <linux/types.h>
7 #include <linux/errno.h>
8 #include <linux/signal.h>
9 #include <linux/sched/signal.h>
10 #include <linux/sched/task.h>
11 #include <linux/tty.h>
12 #include <linux/fcntl.h>
13 #include <linux/uaccess.h>
16 static int is_ignored(int sig)
18 return (sigismember(¤t->blocked, sig) ||
19 current->sighand->action[sig-1].sa.sa_handler == SIG_IGN);
23 * tty_check_change - check for POSIX terminal changes
25 * @sig: signal to send
27 * If we try to write to, or set the state of, a terminal and we're
28 * not in the foreground, send a SIGTTOU. If the signal is blocked or
29 * ignored, go ahead and perform the operation. (POSIX 7.2)
33 int __tty_check_change(struct tty_struct *tty, int sig)
36 struct pid *pgrp, *tty_pgrp;
39 if (current->signal->tty != tty)
43 pgrp = task_pgrp(current);
45 spin_lock_irqsave(&tty->ctrl_lock, flags);
47 spin_unlock_irqrestore(&tty->ctrl_lock, flags);
49 if (tty_pgrp && pgrp != tty_pgrp) {
50 if (is_ignored(sig)) {
53 } else if (is_current_pgrp_orphaned())
56 kill_pgrp(pgrp, sig, 1);
57 set_thread_flag(TIF_SIGPENDING);
64 tty_warn(tty, "sig=%d, tty->pgrp == NULL!\n", sig);
69 int tty_check_change(struct tty_struct *tty)
71 return __tty_check_change(tty, SIGTTOU);
73 EXPORT_SYMBOL(tty_check_change);
75 void proc_clear_tty(struct task_struct *p)
78 struct tty_struct *tty;
80 spin_lock_irqsave(&p->sighand->siglock, flags);
82 p->signal->tty = NULL;
83 spin_unlock_irqrestore(&p->sighand->siglock, flags);
88 * proc_set_tty - set the controlling terminal
91 * Only callable by the session leader and only if it does not already have
92 * a controlling terminal.
94 * Caller must hold: tty_lock()
95 * a readlock on tasklist_lock
98 static void __proc_set_tty(struct tty_struct *tty)
102 spin_lock_irqsave(&tty->ctrl_lock, flags);
104 * The session and fg pgrp references will be non-NULL if
105 * tiocsctty() is stealing the controlling tty
107 put_pid(tty->session);
109 tty->pgrp = get_pid(task_pgrp(current));
110 tty->session = get_pid(task_session(current));
111 spin_unlock_irqrestore(&tty->ctrl_lock, flags);
112 if (current->signal->tty) {
113 tty_debug(tty, "current tty %s not NULL!!\n",
114 current->signal->tty->name);
115 tty_kref_put(current->signal->tty);
117 put_pid(current->signal->tty_old_pgrp);
118 current->signal->tty = tty_kref_get(tty);
119 current->signal->tty_old_pgrp = NULL;
122 static void proc_set_tty(struct tty_struct *tty)
124 spin_lock_irq(¤t->sighand->siglock);
126 spin_unlock_irq(¤t->sighand->siglock);
130 * Called by tty_open() to set the controlling tty if applicable.
132 void tty_open_proc_set_tty(struct file *filp, struct tty_struct *tty)
134 read_lock(&tasklist_lock);
135 spin_lock_irq(¤t->sighand->siglock);
136 if (current->signal->leader &&
137 !current->signal->tty &&
138 tty->session == NULL) {
140 * Don't let a process that only has write access to the tty
141 * obtain the privileges associated with having a tty as
142 * controlling terminal (being able to reopen it with full
143 * access through /dev/tty, being able to perform pushback).
144 * Many distributions set the group of all ttys to "tty" and
145 * grant write-only access to all terminals for setgid tty
146 * binaries, which should not imply full privileges on all ttys.
148 * This could theoretically break old code that performs open()
149 * on a write-only file descriptor. In that case, it might be
150 * necessary to also permit this if
151 * inode_permission(inode, MAY_READ) == 0.
153 if (filp->f_mode & FMODE_READ)
156 spin_unlock_irq(¤t->sighand->siglock);
157 read_unlock(&tasklist_lock);
160 struct tty_struct *get_current_tty(void)
162 struct tty_struct *tty;
165 spin_lock_irqsave(¤t->sighand->siglock, flags);
166 tty = tty_kref_get(current->signal->tty);
167 spin_unlock_irqrestore(¤t->sighand->siglock, flags);
170 EXPORT_SYMBOL_GPL(get_current_tty);
173 * Called from tty_release().
175 void session_clear_tty(struct pid *session)
177 struct task_struct *p;
179 do_each_pid_task(session, PIDTYPE_SID, p) {
181 } while_each_pid_task(session, PIDTYPE_SID, p);
185 * tty_signal_session_leader - sends SIGHUP to session leader
186 * @tty: controlling tty
187 * @exit_session: if non-zero, signal all foreground group processes
189 * Send SIGHUP and SIGCONT to the session leader and its process group.
190 * Optionally, signal all processes in the foreground process group.
192 * Returns the number of processes in the session with this tty
193 * as their controlling terminal. This value is used to drop
194 * tty references for those processes.
196 int tty_signal_session_leader(struct tty_struct *tty, int exit_session)
198 struct task_struct *p;
200 struct pid *tty_pgrp = NULL;
202 read_lock(&tasklist_lock);
204 do_each_pid_task(tty->session, PIDTYPE_SID, p) {
205 spin_lock_irq(&p->sighand->siglock);
206 if (p->signal->tty == tty) {
207 p->signal->tty = NULL;
209 * We defer the dereferences outside of
214 if (!p->signal->leader) {
215 spin_unlock_irq(&p->sighand->siglock);
218 __group_send_sig_info(SIGHUP, SEND_SIG_PRIV, p);
219 __group_send_sig_info(SIGCONT, SEND_SIG_PRIV, p);
220 put_pid(p->signal->tty_old_pgrp); /* A noop */
221 spin_lock(&tty->ctrl_lock);
222 tty_pgrp = get_pid(tty->pgrp);
224 p->signal->tty_old_pgrp = get_pid(tty->pgrp);
225 spin_unlock(&tty->ctrl_lock);
226 spin_unlock_irq(&p->sighand->siglock);
227 } while_each_pid_task(tty->session, PIDTYPE_SID, p);
229 read_unlock(&tasklist_lock);
233 kill_pgrp(tty_pgrp, SIGHUP, exit_session);
241 * disassociate_ctty - disconnect controlling tty
242 * @on_exit: true if exiting so need to "hang up" the session
244 * This function is typically called only by the session leader, when
245 * it wants to disassociate itself from its controlling tty.
247 * It performs the following functions:
248 * (1) Sends a SIGHUP and SIGCONT to the foreground process group
249 * (2) Clears the tty from being controlling the session
250 * (3) Clears the controlling tty for all processes in the
253 * The argument on_exit is set to 1 if called when a process is
254 * exiting; it is 0 if called by the ioctl TIOCNOTTY.
257 * BTM is taken for hysterical raisons, and held when
258 * called from no_tty().
259 * tty_mutex is taken to protect tty
260 * ->siglock is taken to protect ->signal/->sighand
261 * tasklist_lock is taken to walk process list for sessions
262 * ->siglock is taken to protect ->signal/->sighand
264 void disassociate_ctty(int on_exit)
266 struct tty_struct *tty;
268 if (!current->signal->leader)
271 tty = get_current_tty();
273 if (on_exit && tty->driver->type != TTY_DRIVER_TYPE_PTY) {
274 tty_vhangup_session(tty);
276 struct pid *tty_pgrp = tty_get_pgrp(tty);
279 kill_pgrp(tty_pgrp, SIGHUP, on_exit);
281 kill_pgrp(tty_pgrp, SIGCONT, on_exit);
287 } else if (on_exit) {
288 struct pid *old_pgrp;
290 spin_lock_irq(¤t->sighand->siglock);
291 old_pgrp = current->signal->tty_old_pgrp;
292 current->signal->tty_old_pgrp = NULL;
293 spin_unlock_irq(¤t->sighand->siglock);
295 kill_pgrp(old_pgrp, SIGHUP, on_exit);
296 kill_pgrp(old_pgrp, SIGCONT, on_exit);
302 spin_lock_irq(¤t->sighand->siglock);
303 put_pid(current->signal->tty_old_pgrp);
304 current->signal->tty_old_pgrp = NULL;
305 tty = tty_kref_get(current->signal->tty);
306 spin_unlock_irq(¤t->sighand->siglock);
312 spin_lock_irqsave(&tty->ctrl_lock, flags);
313 put_pid(tty->session);
317 spin_unlock_irqrestore(&tty->ctrl_lock, flags);
322 /* Now clear signal->tty under the lock */
323 read_lock(&tasklist_lock);
324 session_clear_tty(task_session(current));
325 read_unlock(&tasklist_lock);
330 * no_tty - Ensure the current process does not have a controlling tty
335 * FIXME: Review locking here. The tty_lock never covered any race
336 * between a new association and proc_clear_tty but possibly we need
337 * to protect against this anyway.
339 struct task_struct *tsk = current;
341 disassociate_ctty(0);
346 * tiocsctty - set controlling tty
347 * @tty: tty structure
348 * @file: file structure used to check permissions
349 * @arg: user argument
351 * This ioctl is used to manage job control. It permits a session
352 * leader to set this tty as the controlling tty for the session.
355 * Takes tty_lock() to serialize proc_set_tty() for this tty
356 * Takes tasklist_lock internally to walk sessions
357 * Takes ->siglock() when updating signal->tty
359 static int tiocsctty(struct tty_struct *tty, struct file *file, int arg)
364 read_lock(&tasklist_lock);
366 if (current->signal->leader && (task_session(current) == tty->session))
370 * The process must be a session leader and
371 * not have a controlling tty already.
373 if (!current->signal->leader || current->signal->tty) {
380 * This tty is already the controlling
381 * tty for another session group!
383 if (arg == 1 && capable(CAP_SYS_ADMIN)) {
387 session_clear_tty(tty->session);
394 /* See the comment in tty_open_proc_set_tty(). */
395 if ((file->f_mode & FMODE_READ) == 0 && !capable(CAP_SYS_ADMIN)) {
402 read_unlock(&tasklist_lock);
408 * tty_get_pgrp - return a ref counted pgrp pid
411 * Returns a refcounted instance of the pid struct for the process
412 * group controlling the tty.
414 struct pid *tty_get_pgrp(struct tty_struct *tty)
419 spin_lock_irqsave(&tty->ctrl_lock, flags);
420 pgrp = get_pid(tty->pgrp);
421 spin_unlock_irqrestore(&tty->ctrl_lock, flags);
425 EXPORT_SYMBOL_GPL(tty_get_pgrp);
428 * This checks not only the pgrp, but falls back on the pid if no
429 * satisfactory pgrp is found. I dunno - gdb doesn't work correctly
432 * The caller must hold rcu lock or the tasklist lock.
434 static struct pid *session_of_pgrp(struct pid *pgrp)
436 struct task_struct *p;
437 struct pid *sid = NULL;
439 p = pid_task(pgrp, PIDTYPE_PGID);
441 p = pid_task(pgrp, PIDTYPE_PID);
443 sid = task_session(p);
449 * tiocgpgrp - get process group
450 * @tty: tty passed by user
451 * @real_tty: tty side of the tty passed by the user if a pty else the tty
454 * Obtain the process group of the tty. If there is no process group
457 * Locking: none. Reference to current->signal->tty is safe.
459 static int tiocgpgrp(struct tty_struct *tty, struct tty_struct *real_tty, pid_t __user *p)
464 * (tty == real_tty) is a cheap way of
465 * testing if the tty is NOT a master pty.
467 if (tty == real_tty && current->signal->tty != real_tty)
469 pid = tty_get_pgrp(real_tty);
470 ret = put_user(pid_vnr(pid), p);
476 * tiocspgrp - attempt to set process group
477 * @tty: tty passed by user
478 * @real_tty: tty side device matching tty passed by user
481 * Set the process group of the tty to the session passed. Only
482 * permitted where the tty session is our session.
484 * Locking: RCU, ctrl lock
486 static int tiocspgrp(struct tty_struct *tty, struct tty_struct *real_tty, pid_t __user *p)
490 int retval = tty_check_change(real_tty);
497 if (get_user(pgrp_nr, p))
502 spin_lock_irq(&real_tty->ctrl_lock);
503 if (!current->signal->tty ||
504 (current->signal->tty != real_tty) ||
505 (real_tty->session != task_session(current))) {
507 goto out_unlock_ctrl;
510 pgrp = find_vpid(pgrp_nr);
515 if (session_of_pgrp(pgrp) != task_session(current))
518 put_pid(real_tty->pgrp);
519 real_tty->pgrp = get_pid(pgrp);
523 spin_unlock_irq(&real_tty->ctrl_lock);
528 * tiocgsid - get session id
529 * @tty: tty passed by user
530 * @real_tty: tty side of the tty passed by the user if a pty else the tty
531 * @p: pointer to returned session id
533 * Obtain the session id of the tty. If there is no session
536 static int tiocgsid(struct tty_struct *tty, struct tty_struct *real_tty, pid_t __user *p)
542 * (tty == real_tty) is a cheap way of
543 * testing if the tty is NOT a master pty.
545 if (tty == real_tty && current->signal->tty != real_tty)
548 spin_lock_irqsave(&real_tty->ctrl_lock, flags);
549 if (!real_tty->session)
551 sid = pid_vnr(real_tty->session);
552 spin_unlock_irqrestore(&real_tty->ctrl_lock, flags);
554 return put_user(sid, p);
557 spin_unlock_irqrestore(&real_tty->ctrl_lock, flags);
562 * Called from tty_ioctl(). If tty is a pty then real_tty is the slave side,
563 * if not then tty == real_tty.
565 long tty_jobctrl_ioctl(struct tty_struct *tty, struct tty_struct *real_tty,
566 struct file *file, unsigned int cmd, unsigned long arg)
568 void __user *p = (void __user *)arg;
572 if (current->signal->tty != tty)
577 return tiocsctty(real_tty, file, arg);
579 return tiocgpgrp(tty, real_tty, p);
581 return tiocspgrp(tty, real_tty, p);
583 return tiocgsid(tty, real_tty, p);