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>
15 static int is_ignored(int sig)
17 return (sigismember(¤t->blocked, sig) ||
18 current->sighand->action[sig-1].sa.sa_handler == SIG_IGN);
22 * tty_check_change - check for POSIX terminal changes
25 * If we try to write to, or set the state of, a terminal and we're
26 * not in the foreground, send a SIGTTOU. If the signal is blocked or
27 * ignored, go ahead and perform the operation. (POSIX 7.2)
31 int __tty_check_change(struct tty_struct *tty, int sig)
34 struct pid *pgrp, *tty_pgrp;
37 if (current->signal->tty != tty)
41 pgrp = task_pgrp(current);
43 spin_lock_irqsave(&tty->ctrl_lock, flags);
45 spin_unlock_irqrestore(&tty->ctrl_lock, flags);
47 if (tty_pgrp && pgrp != tty_pgrp) {
48 if (is_ignored(sig)) {
51 } else if (is_current_pgrp_orphaned())
54 kill_pgrp(pgrp, sig, 1);
55 set_thread_flag(TIF_SIGPENDING);
62 tty_warn(tty, "sig=%d, tty->pgrp == NULL!\n", sig);
67 int tty_check_change(struct tty_struct *tty)
69 return __tty_check_change(tty, SIGTTOU);
71 EXPORT_SYMBOL(tty_check_change);
73 void proc_clear_tty(struct task_struct *p)
76 struct tty_struct *tty;
77 spin_lock_irqsave(&p->sighand->siglock, flags);
79 p->signal->tty = NULL;
80 spin_unlock_irqrestore(&p->sighand->siglock, flags);
85 * proc_set_tty - set the controlling terminal
87 * Only callable by the session leader and only if it does not already have
88 * a controlling terminal.
90 * Caller must hold: tty_lock()
91 * a readlock on tasklist_lock
94 static void __proc_set_tty(struct tty_struct *tty)
98 spin_lock_irqsave(&tty->ctrl_lock, flags);
100 * The session and fg pgrp references will be non-NULL if
101 * tiocsctty() is stealing the controlling tty
103 put_pid(tty->session);
105 tty->pgrp = get_pid(task_pgrp(current));
106 spin_unlock_irqrestore(&tty->ctrl_lock, flags);
107 tty->session = get_pid(task_session(current));
108 if (current->signal->tty) {
109 tty_debug(tty, "current tty %s not NULL!!\n",
110 current->signal->tty->name);
111 tty_kref_put(current->signal->tty);
113 put_pid(current->signal->tty_old_pgrp);
114 current->signal->tty = tty_kref_get(tty);
115 current->signal->tty_old_pgrp = NULL;
118 static void proc_set_tty(struct tty_struct *tty)
120 spin_lock_irq(¤t->sighand->siglock);
122 spin_unlock_irq(¤t->sighand->siglock);
126 * Called by tty_open() to set the controlling tty if applicable.
128 void tty_open_proc_set_tty(struct file *filp, struct tty_struct *tty)
130 read_lock(&tasklist_lock);
131 spin_lock_irq(¤t->sighand->siglock);
132 if (current->signal->leader &&
133 !current->signal->tty &&
134 tty->session == NULL) {
136 * Don't let a process that only has write access to the tty
137 * obtain the privileges associated with having a tty as
138 * controlling terminal (being able to reopen it with full
139 * access through /dev/tty, being able to perform pushback).
140 * Many distributions set the group of all ttys to "tty" and
141 * grant write-only access to all terminals for setgid tty
142 * binaries, which should not imply full privileges on all ttys.
144 * This could theoretically break old code that performs open()
145 * on a write-only file descriptor. In that case, it might be
146 * necessary to also permit this if
147 * inode_permission(inode, MAY_READ) == 0.
149 if (filp->f_mode & FMODE_READ)
152 spin_unlock_irq(¤t->sighand->siglock);
153 read_unlock(&tasklist_lock);
156 struct tty_struct *get_current_tty(void)
158 struct tty_struct *tty;
161 spin_lock_irqsave(¤t->sighand->siglock, flags);
162 tty = tty_kref_get(current->signal->tty);
163 spin_unlock_irqrestore(¤t->sighand->siglock, flags);
166 EXPORT_SYMBOL_GPL(get_current_tty);
169 * Called from tty_release().
171 void session_clear_tty(struct pid *session)
173 struct task_struct *p;
174 do_each_pid_task(session, PIDTYPE_SID, p) {
176 } while_each_pid_task(session, PIDTYPE_SID, p);
180 * tty_signal_session_leader - sends SIGHUP to session leader
181 * @tty controlling tty
182 * @exit_session if non-zero, signal all foreground group processes
184 * Send SIGHUP and SIGCONT to the session leader and its process group.
185 * Optionally, signal all processes in the foreground process group.
187 * Returns the number of processes in the session with this tty
188 * as their controlling terminal. This value is used to drop
189 * tty references for those processes.
191 int tty_signal_session_leader(struct tty_struct *tty, int exit_session)
193 struct task_struct *p;
195 struct pid *tty_pgrp = NULL;
197 read_lock(&tasklist_lock);
199 do_each_pid_task(tty->session, PIDTYPE_SID, p) {
200 spin_lock_irq(&p->sighand->siglock);
201 if (p->signal->tty == tty) {
202 p->signal->tty = NULL;
203 /* We defer the dereferences outside fo
207 if (!p->signal->leader) {
208 spin_unlock_irq(&p->sighand->siglock);
211 __group_send_sig_info(SIGHUP, SEND_SIG_PRIV, p);
212 __group_send_sig_info(SIGCONT, SEND_SIG_PRIV, p);
213 put_pid(p->signal->tty_old_pgrp); /* A noop */
214 spin_lock(&tty->ctrl_lock);
215 tty_pgrp = get_pid(tty->pgrp);
217 p->signal->tty_old_pgrp = get_pid(tty->pgrp);
218 spin_unlock(&tty->ctrl_lock);
219 spin_unlock_irq(&p->sighand->siglock);
220 } while_each_pid_task(tty->session, PIDTYPE_SID, p);
222 read_unlock(&tasklist_lock);
226 kill_pgrp(tty_pgrp, SIGHUP, exit_session);
234 * disassociate_ctty - disconnect controlling tty
235 * @on_exit: true if exiting so need to "hang up" the session
237 * This function is typically called only by the session leader, when
238 * it wants to disassociate itself from its controlling tty.
240 * It performs the following functions:
241 * (1) Sends a SIGHUP and SIGCONT to the foreground process group
242 * (2) Clears the tty from being controlling the session
243 * (3) Clears the controlling tty for all processes in the
246 * The argument on_exit is set to 1 if called when a process is
247 * exiting; it is 0 if called by the ioctl TIOCNOTTY.
250 * BTM is taken for hysterical raisons, and held when
251 * called from no_tty().
252 * tty_mutex is taken to protect tty
253 * ->siglock is taken to protect ->signal/->sighand
254 * tasklist_lock is taken to walk process list for sessions
255 * ->siglock is taken to protect ->signal/->sighand
257 void disassociate_ctty(int on_exit)
259 struct tty_struct *tty;
261 if (!current->signal->leader)
264 tty = get_current_tty();
266 if (on_exit && tty->driver->type != TTY_DRIVER_TYPE_PTY) {
267 tty_vhangup_session(tty);
269 struct pid *tty_pgrp = tty_get_pgrp(tty);
271 kill_pgrp(tty_pgrp, SIGHUP, on_exit);
273 kill_pgrp(tty_pgrp, SIGCONT, on_exit);
279 } else if (on_exit) {
280 struct pid *old_pgrp;
281 spin_lock_irq(¤t->sighand->siglock);
282 old_pgrp = current->signal->tty_old_pgrp;
283 current->signal->tty_old_pgrp = NULL;
284 spin_unlock_irq(¤t->sighand->siglock);
286 kill_pgrp(old_pgrp, SIGHUP, on_exit);
287 kill_pgrp(old_pgrp, SIGCONT, on_exit);
293 spin_lock_irq(¤t->sighand->siglock);
294 put_pid(current->signal->tty_old_pgrp);
295 current->signal->tty_old_pgrp = NULL;
297 tty = tty_kref_get(current->signal->tty);
300 spin_lock_irqsave(&tty->ctrl_lock, flags);
301 put_pid(tty->session);
305 spin_unlock_irqrestore(&tty->ctrl_lock, flags);
309 spin_unlock_irq(¤t->sighand->siglock);
310 /* Now clear signal->tty under the lock */
311 read_lock(&tasklist_lock);
312 session_clear_tty(task_session(current));
313 read_unlock(&tasklist_lock);
318 * no_tty - Ensure the current process does not have a controlling tty
322 /* FIXME: Review locking here. The tty_lock never covered any race
323 between a new association and proc_clear_tty but possible we need
324 to protect against this anyway */
325 struct task_struct *tsk = current;
326 disassociate_ctty(0);
331 * tiocsctty - set controlling tty
332 * @tty: tty structure
333 * @arg: user argument
335 * This ioctl is used to manage job control. It permits a session
336 * leader to set this tty as the controlling tty for the session.
339 * Takes tty_lock() to serialize proc_set_tty() for this tty
340 * Takes tasklist_lock internally to walk sessions
341 * Takes ->siglock() when updating signal->tty
343 static int tiocsctty(struct tty_struct *tty, struct file *file, int arg)
348 read_lock(&tasklist_lock);
350 if (current->signal->leader && (task_session(current) == tty->session))
354 * The process must be a session leader and
355 * not have a controlling tty already.
357 if (!current->signal->leader || current->signal->tty) {
364 * This tty is already the controlling
365 * tty for another session group!
367 if (arg == 1 && capable(CAP_SYS_ADMIN)) {
371 session_clear_tty(tty->session);
378 /* See the comment in tty_open_proc_set_tty(). */
379 if ((file->f_mode & FMODE_READ) == 0 && !capable(CAP_SYS_ADMIN)) {
386 read_unlock(&tasklist_lock);
392 * tty_get_pgrp - return a ref counted pgrp pid
395 * Returns a refcounted instance of the pid struct for the process
396 * group controlling the tty.
398 struct pid *tty_get_pgrp(struct tty_struct *tty)
403 spin_lock_irqsave(&tty->ctrl_lock, flags);
404 pgrp = get_pid(tty->pgrp);
405 spin_unlock_irqrestore(&tty->ctrl_lock, flags);
409 EXPORT_SYMBOL_GPL(tty_get_pgrp);
412 * This checks not only the pgrp, but falls back on the pid if no
413 * satisfactory pgrp is found. I dunno - gdb doesn't work correctly
416 * The caller must hold rcu lock or the tasklist lock.
418 static struct pid *session_of_pgrp(struct pid *pgrp)
420 struct task_struct *p;
421 struct pid *sid = NULL;
423 p = pid_task(pgrp, PIDTYPE_PGID);
425 p = pid_task(pgrp, PIDTYPE_PID);
427 sid = task_session(p);
433 * tiocgpgrp - get process group
434 * @tty: tty passed by user
435 * @real_tty: tty side of the tty passed by the user if a pty else the tty
438 * Obtain the process group of the tty. If there is no process group
441 * Locking: none. Reference to current->signal->tty is safe.
443 static int tiocgpgrp(struct tty_struct *tty, struct tty_struct *real_tty, pid_t __user *p)
448 * (tty == real_tty) is a cheap way of
449 * testing if the tty is NOT a master pty.
451 if (tty == real_tty && current->signal->tty != real_tty)
453 pid = tty_get_pgrp(real_tty);
454 ret = put_user(pid_vnr(pid), p);
460 * tiocspgrp - attempt to set process group
461 * @tty: tty passed by user
462 * @real_tty: tty side device matching tty passed by user
465 * Set the process group of the tty to the session passed. Only
466 * permitted where the tty session is our session.
468 * Locking: RCU, ctrl lock
470 static int tiocspgrp(struct tty_struct *tty, struct tty_struct *real_tty, pid_t __user *p)
474 int retval = tty_check_change(real_tty);
480 if (!current->signal->tty ||
481 (current->signal->tty != real_tty) ||
482 (real_tty->session != task_session(current)))
484 if (get_user(pgrp_nr, p))
489 pgrp = find_vpid(pgrp_nr);
494 if (session_of_pgrp(pgrp) != task_session(current))
497 spin_lock_irq(&tty->ctrl_lock);
498 put_pid(real_tty->pgrp);
499 real_tty->pgrp = get_pid(pgrp);
500 spin_unlock_irq(&tty->ctrl_lock);
507 * tiocgsid - get session id
508 * @tty: tty passed by user
509 * @real_tty: tty side of the tty passed by the user if a pty else the tty
510 * @p: pointer to returned session id
512 * Obtain the session id of the tty. If there is no session
515 * Locking: none. Reference to current->signal->tty is safe.
517 static int tiocgsid(struct tty_struct *tty, struct tty_struct *real_tty, pid_t __user *p)
520 * (tty == real_tty) is a cheap way of
521 * testing if the tty is NOT a master pty.
523 if (tty == real_tty && current->signal->tty != real_tty)
525 if (!real_tty->session)
527 return put_user(pid_vnr(real_tty->session), p);
531 * Called from tty_ioctl(). If tty is a pty then real_tty is the slave side,
532 * if not then tty == real_tty.
534 long tty_jobctrl_ioctl(struct tty_struct *tty, struct tty_struct *real_tty,
535 struct file *file, unsigned int cmd, unsigned long arg)
537 void __user *p = (void __user *)arg;
541 if (current->signal->tty != tty)
546 return tiocsctty(real_tty, file, arg);
548 return tiocgpgrp(tty, real_tty, p);
550 return tiocspgrp(tty, real_tty, p);
552 return tiocgsid(tty, real_tty, p);