Line data Source code
1 : // SPDX-License-Identifier: GPL-2.0
2 : /*
3 : * Copyright (C) 1991, 1992 Linus Torvalds
4 : */
5 :
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>
14 : #include "tty.h"
15 :
16 : static int is_ignored(int sig)
17 : {
18 0 : return (sigismember(¤t->blocked, sig) ||
19 0 : current->sighand->action[sig-1].sa.sa_handler == SIG_IGN);
20 : }
21 :
22 : /**
23 : * __tty_check_change - check for POSIX terminal changes
24 : * @tty: tty to check
25 : * @sig: signal to send
26 : *
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)
30 : *
31 : * Locking: ctrl.lock
32 : */
33 0 : int __tty_check_change(struct tty_struct *tty, int sig)
34 : {
35 : unsigned long flags;
36 : struct pid *pgrp, *tty_pgrp;
37 0 : int ret = 0;
38 :
39 0 : if (current->signal->tty != tty)
40 : return 0;
41 :
42 : rcu_read_lock();
43 0 : pgrp = task_pgrp(current);
44 :
45 0 : spin_lock_irqsave(&tty->ctrl.lock, flags);
46 0 : tty_pgrp = tty->ctrl.pgrp;
47 0 : spin_unlock_irqrestore(&tty->ctrl.lock, flags);
48 :
49 0 : if (tty_pgrp && pgrp != tty_pgrp) {
50 0 : if (is_ignored(sig)) {
51 0 : if (sig == SIGTTIN)
52 0 : ret = -EIO;
53 0 : } else if (is_current_pgrp_orphaned())
54 : ret = -EIO;
55 : else {
56 0 : kill_pgrp(pgrp, sig, 1);
57 0 : set_thread_flag(TIF_SIGPENDING);
58 0 : ret = -ERESTARTSYS;
59 : }
60 : }
61 : rcu_read_unlock();
62 :
63 0 : if (!tty_pgrp)
64 0 : tty_warn(tty, "sig=%d, tty->pgrp == NULL!\n", sig);
65 :
66 : return ret;
67 : }
68 :
69 0 : int tty_check_change(struct tty_struct *tty)
70 : {
71 0 : return __tty_check_change(tty, SIGTTOU);
72 : }
73 : EXPORT_SYMBOL(tty_check_change);
74 :
75 0 : void proc_clear_tty(struct task_struct *p)
76 : {
77 : unsigned long flags;
78 : struct tty_struct *tty;
79 :
80 0 : spin_lock_irqsave(&p->sighand->siglock, flags);
81 0 : tty = p->signal->tty;
82 0 : p->signal->tty = NULL;
83 0 : spin_unlock_irqrestore(&p->sighand->siglock, flags);
84 0 : tty_kref_put(tty);
85 0 : }
86 :
87 : /**
88 : * __proc_set_tty - set the controlling terminal
89 : * @tty: tty structure
90 : *
91 : * Only callable by the session leader and only if it does not already have
92 : * a controlling terminal.
93 : *
94 : * Caller must hold: tty_lock()
95 : * a readlock on tasklist_lock
96 : * sighand lock
97 : */
98 0 : static void __proc_set_tty(struct tty_struct *tty)
99 : {
100 : unsigned long flags;
101 :
102 0 : spin_lock_irqsave(&tty->ctrl.lock, flags);
103 : /*
104 : * The session and fg pgrp references will be non-NULL if
105 : * tiocsctty() is stealing the controlling tty
106 : */
107 0 : put_pid(tty->ctrl.session);
108 0 : put_pid(tty->ctrl.pgrp);
109 0 : tty->ctrl.pgrp = get_pid(task_pgrp(current));
110 0 : tty->ctrl.session = get_pid(task_session(current));
111 0 : spin_unlock_irqrestore(&tty->ctrl.lock, flags);
112 0 : if (current->signal->tty) {
113 : tty_debug(tty, "current tty %s not NULL!!\n",
114 : current->signal->tty->name);
115 0 : tty_kref_put(current->signal->tty);
116 : }
117 0 : put_pid(current->signal->tty_old_pgrp);
118 0 : current->signal->tty = tty_kref_get(tty);
119 0 : current->signal->tty_old_pgrp = NULL;
120 0 : }
121 :
122 : static void proc_set_tty(struct tty_struct *tty)
123 : {
124 0 : spin_lock_irq(¤t->sighand->siglock);
125 0 : __proc_set_tty(tty);
126 0 : spin_unlock_irq(¤t->sighand->siglock);
127 : }
128 :
129 : /*
130 : * Called by tty_open() to set the controlling tty if applicable.
131 : */
132 0 : void tty_open_proc_set_tty(struct file *filp, struct tty_struct *tty)
133 : {
134 0 : read_lock(&tasklist_lock);
135 0 : spin_lock_irq(¤t->sighand->siglock);
136 0 : if (current->signal->leader &&
137 0 : !current->signal->tty &&
138 0 : tty->ctrl.session == NULL) {
139 : /*
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.
147 : *
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.
152 : */
153 0 : if (filp->f_mode & FMODE_READ)
154 0 : __proc_set_tty(tty);
155 : }
156 0 : spin_unlock_irq(¤t->sighand->siglock);
157 0 : read_unlock(&tasklist_lock);
158 0 : }
159 :
160 0 : struct tty_struct *get_current_tty(void)
161 : {
162 : struct tty_struct *tty;
163 : unsigned long flags;
164 :
165 0 : spin_lock_irqsave(¤t->sighand->siglock, flags);
166 0 : tty = tty_kref_get(current->signal->tty);
167 0 : spin_unlock_irqrestore(¤t->sighand->siglock, flags);
168 0 : return tty;
169 : }
170 : EXPORT_SYMBOL_GPL(get_current_tty);
171 :
172 : /*
173 : * Called from tty_release().
174 : */
175 0 : void session_clear_tty(struct pid *session)
176 : {
177 : struct task_struct *p;
178 :
179 0 : do_each_pid_task(session, PIDTYPE_SID, p) {
180 0 : proc_clear_tty(p);
181 : } while_each_pid_task(session, PIDTYPE_SID, p);
182 0 : }
183 :
184 : /**
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
188 : *
189 : * Send SIGHUP and SIGCONT to the session leader and its process group.
190 : * Optionally, signal all processes in the foreground process group.
191 : *
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.
195 : */
196 0 : int tty_signal_session_leader(struct tty_struct *tty, int exit_session)
197 : {
198 : struct task_struct *p;
199 0 : int refs = 0;
200 0 : struct pid *tty_pgrp = NULL;
201 :
202 0 : read_lock(&tasklist_lock);
203 0 : if (tty->ctrl.session) {
204 0 : do_each_pid_task(tty->ctrl.session, PIDTYPE_SID, p) {
205 0 : spin_lock_irq(&p->sighand->siglock);
206 0 : if (p->signal->tty == tty) {
207 0 : p->signal->tty = NULL;
208 : /*
209 : * We defer the dereferences outside of
210 : * the tasklist lock.
211 : */
212 0 : refs++;
213 : }
214 0 : if (!p->signal->leader) {
215 0 : spin_unlock_irq(&p->sighand->siglock);
216 0 : continue;
217 : }
218 0 : send_signal_locked(SIGHUP, SEND_SIG_PRIV, p, PIDTYPE_TGID);
219 0 : send_signal_locked(SIGCONT, SEND_SIG_PRIV, p, PIDTYPE_TGID);
220 0 : put_pid(p->signal->tty_old_pgrp); /* A noop */
221 0 : spin_lock(&tty->ctrl.lock);
222 0 : tty_pgrp = get_pid(tty->ctrl.pgrp);
223 0 : if (tty->ctrl.pgrp)
224 0 : p->signal->tty_old_pgrp =
225 0 : get_pid(tty->ctrl.pgrp);
226 0 : spin_unlock(&tty->ctrl.lock);
227 0 : spin_unlock_irq(&p->sighand->siglock);
228 : } while_each_pid_task(tty->ctrl.session, PIDTYPE_SID, p);
229 : }
230 0 : read_unlock(&tasklist_lock);
231 :
232 0 : if (tty_pgrp) {
233 0 : if (exit_session)
234 0 : kill_pgrp(tty_pgrp, SIGHUP, exit_session);
235 0 : put_pid(tty_pgrp);
236 : }
237 :
238 0 : return refs;
239 : }
240 :
241 : /**
242 : * disassociate_ctty - disconnect controlling tty
243 : * @on_exit: true if exiting so need to "hang up" the session
244 : *
245 : * This function is typically called only by the session leader, when
246 : * it wants to disassociate itself from its controlling tty.
247 : *
248 : * It performs the following functions:
249 : * (1) Sends a SIGHUP and SIGCONT to the foreground process group
250 : * (2) Clears the tty from being controlling the session
251 : * (3) Clears the controlling tty for all processes in the
252 : * session group.
253 : *
254 : * The argument on_exit is set to 1 if called when a process is
255 : * exiting; it is 0 if called by the ioctl TIOCNOTTY.
256 : *
257 : * Locking:
258 : * BTM is taken for hysterical raisons, and held when
259 : * called from no_tty().
260 : * tty_mutex is taken to protect tty
261 : * ->siglock is taken to protect ->signal/->sighand
262 : * tasklist_lock is taken to walk process list for sessions
263 : * ->siglock is taken to protect ->signal/->sighand
264 : */
265 367 : void disassociate_ctty(int on_exit)
266 : {
267 : struct tty_struct *tty;
268 :
269 367 : if (!current->signal->leader)
270 : return;
271 :
272 0 : tty = get_current_tty();
273 0 : if (tty) {
274 0 : if (on_exit && tty->driver->type != TTY_DRIVER_TYPE_PTY) {
275 0 : tty_vhangup_session(tty);
276 : } else {
277 0 : struct pid *tty_pgrp = tty_get_pgrp(tty);
278 :
279 0 : if (tty_pgrp) {
280 0 : kill_pgrp(tty_pgrp, SIGHUP, on_exit);
281 0 : if (!on_exit)
282 0 : kill_pgrp(tty_pgrp, SIGCONT, on_exit);
283 0 : put_pid(tty_pgrp);
284 : }
285 : }
286 0 : tty_kref_put(tty);
287 :
288 0 : } else if (on_exit) {
289 : struct pid *old_pgrp;
290 :
291 0 : spin_lock_irq(¤t->sighand->siglock);
292 0 : old_pgrp = current->signal->tty_old_pgrp;
293 0 : current->signal->tty_old_pgrp = NULL;
294 0 : spin_unlock_irq(¤t->sighand->siglock);
295 0 : if (old_pgrp) {
296 0 : kill_pgrp(old_pgrp, SIGHUP, on_exit);
297 0 : kill_pgrp(old_pgrp, SIGCONT, on_exit);
298 0 : put_pid(old_pgrp);
299 : }
300 : return;
301 : }
302 :
303 0 : spin_lock_irq(¤t->sighand->siglock);
304 0 : put_pid(current->signal->tty_old_pgrp);
305 0 : current->signal->tty_old_pgrp = NULL;
306 0 : tty = tty_kref_get(current->signal->tty);
307 0 : spin_unlock_irq(¤t->sighand->siglock);
308 :
309 0 : if (tty) {
310 : unsigned long flags;
311 :
312 0 : tty_lock(tty);
313 0 : spin_lock_irqsave(&tty->ctrl.lock, flags);
314 0 : put_pid(tty->ctrl.session);
315 0 : put_pid(tty->ctrl.pgrp);
316 0 : tty->ctrl.session = NULL;
317 0 : tty->ctrl.pgrp = NULL;
318 0 : spin_unlock_irqrestore(&tty->ctrl.lock, flags);
319 0 : tty_unlock(tty);
320 0 : tty_kref_put(tty);
321 : }
322 :
323 : /* Now clear signal->tty under the lock */
324 0 : read_lock(&tasklist_lock);
325 0 : session_clear_tty(task_session(current));
326 0 : read_unlock(&tasklist_lock);
327 : }
328 :
329 : /*
330 : *
331 : * no_tty - Ensure the current process does not have a controlling tty
332 : */
333 0 : void no_tty(void)
334 : {
335 : /*
336 : * FIXME: Review locking here. The tty_lock never covered any race
337 : * between a new association and proc_clear_tty but possibly we need
338 : * to protect against this anyway.
339 : */
340 0 : struct task_struct *tsk = current;
341 :
342 0 : disassociate_ctty(0);
343 0 : proc_clear_tty(tsk);
344 0 : }
345 :
346 : /**
347 : * tiocsctty - set controlling tty
348 : * @tty: tty structure
349 : * @file: file structure used to check permissions
350 : * @arg: user argument
351 : *
352 : * This ioctl is used to manage job control. It permits a session
353 : * leader to set this tty as the controlling tty for the session.
354 : *
355 : * Locking:
356 : * Takes tty_lock() to serialize proc_set_tty() for this tty
357 : * Takes tasklist_lock internally to walk sessions
358 : * Takes ->siglock() when updating signal->tty
359 : */
360 0 : static int tiocsctty(struct tty_struct *tty, struct file *file, int arg)
361 : {
362 0 : int ret = 0;
363 :
364 0 : tty_lock(tty);
365 0 : read_lock(&tasklist_lock);
366 :
367 0 : if (current->signal->leader &&
368 0 : task_session(current) == tty->ctrl.session)
369 : goto unlock;
370 :
371 : /*
372 : * The process must be a session leader and
373 : * not have a controlling tty already.
374 : */
375 0 : if (!current->signal->leader || current->signal->tty) {
376 : ret = -EPERM;
377 : goto unlock;
378 : }
379 :
380 0 : if (tty->ctrl.session) {
381 : /*
382 : * This tty is already the controlling
383 : * tty for another session group!
384 : */
385 0 : if (arg == 1 && capable(CAP_SYS_ADMIN)) {
386 : /*
387 : * Steal it away
388 : */
389 0 : session_clear_tty(tty->ctrl.session);
390 : } else {
391 : ret = -EPERM;
392 : goto unlock;
393 : }
394 : }
395 :
396 : /* See the comment in tty_open_proc_set_tty(). */
397 0 : if ((file->f_mode & FMODE_READ) == 0 && !capable(CAP_SYS_ADMIN)) {
398 : ret = -EPERM;
399 : goto unlock;
400 : }
401 :
402 : proc_set_tty(tty);
403 : unlock:
404 0 : read_unlock(&tasklist_lock);
405 0 : tty_unlock(tty);
406 0 : return ret;
407 : }
408 :
409 : /**
410 : * tty_get_pgrp - return a ref counted pgrp pid
411 : * @tty: tty to read
412 : *
413 : * Returns a refcounted instance of the pid struct for the process
414 : * group controlling the tty.
415 : */
416 0 : struct pid *tty_get_pgrp(struct tty_struct *tty)
417 : {
418 : unsigned long flags;
419 : struct pid *pgrp;
420 :
421 0 : spin_lock_irqsave(&tty->ctrl.lock, flags);
422 0 : pgrp = get_pid(tty->ctrl.pgrp);
423 0 : spin_unlock_irqrestore(&tty->ctrl.lock, flags);
424 :
425 0 : return pgrp;
426 : }
427 : EXPORT_SYMBOL_GPL(tty_get_pgrp);
428 :
429 : /*
430 : * This checks not only the pgrp, but falls back on the pid if no
431 : * satisfactory pgrp is found. I dunno - gdb doesn't work correctly
432 : * without this...
433 : *
434 : * The caller must hold rcu lock or the tasklist lock.
435 : */
436 0 : static struct pid *session_of_pgrp(struct pid *pgrp)
437 : {
438 : struct task_struct *p;
439 0 : struct pid *sid = NULL;
440 :
441 0 : p = pid_task(pgrp, PIDTYPE_PGID);
442 0 : if (p == NULL)
443 0 : p = pid_task(pgrp, PIDTYPE_PID);
444 0 : if (p != NULL)
445 0 : sid = task_session(p);
446 :
447 0 : return sid;
448 : }
449 :
450 : /**
451 : * tiocgpgrp - get process group
452 : * @tty: tty passed by user
453 : * @real_tty: tty side of the tty passed by the user if a pty else the tty
454 : * @p: returned pid
455 : *
456 : * Obtain the process group of the tty. If there is no process group
457 : * return an error.
458 : *
459 : * Locking: none. Reference to current->signal->tty is safe.
460 : */
461 0 : static int tiocgpgrp(struct tty_struct *tty, struct tty_struct *real_tty, pid_t __user *p)
462 : {
463 : struct pid *pid;
464 : int ret;
465 : /*
466 : * (tty == real_tty) is a cheap way of
467 : * testing if the tty is NOT a master pty.
468 : */
469 0 : if (tty == real_tty && current->signal->tty != real_tty)
470 : return -ENOTTY;
471 0 : pid = tty_get_pgrp(real_tty);
472 0 : ret = put_user(pid_vnr(pid), p);
473 0 : put_pid(pid);
474 0 : return ret;
475 : }
476 :
477 : /**
478 : * tiocspgrp - attempt to set process group
479 : * @tty: tty passed by user
480 : * @real_tty: tty side device matching tty passed by user
481 : * @p: pid pointer
482 : *
483 : * Set the process group of the tty to the session passed. Only
484 : * permitted where the tty session is our session.
485 : *
486 : * Locking: RCU, ctrl lock
487 : */
488 0 : static int tiocspgrp(struct tty_struct *tty, struct tty_struct *real_tty, pid_t __user *p)
489 : {
490 : struct pid *pgrp;
491 : pid_t pgrp_nr;
492 0 : int retval = tty_check_change(real_tty);
493 :
494 0 : if (retval == -EIO)
495 : return -ENOTTY;
496 0 : if (retval)
497 : return retval;
498 :
499 0 : if (get_user(pgrp_nr, p))
500 : return -EFAULT;
501 0 : if (pgrp_nr < 0)
502 : return -EINVAL;
503 :
504 0 : spin_lock_irq(&real_tty->ctrl.lock);
505 0 : if (!current->signal->tty ||
506 0 : (current->signal->tty != real_tty) ||
507 0 : (real_tty->ctrl.session != task_session(current))) {
508 : retval = -ENOTTY;
509 : goto out_unlock_ctrl;
510 : }
511 : rcu_read_lock();
512 0 : pgrp = find_vpid(pgrp_nr);
513 0 : retval = -ESRCH;
514 0 : if (!pgrp)
515 : goto out_unlock;
516 0 : retval = -EPERM;
517 0 : if (session_of_pgrp(pgrp) != task_session(current))
518 : goto out_unlock;
519 0 : retval = 0;
520 0 : put_pid(real_tty->ctrl.pgrp);
521 0 : real_tty->ctrl.pgrp = get_pid(pgrp);
522 : out_unlock:
523 : rcu_read_unlock();
524 : out_unlock_ctrl:
525 0 : spin_unlock_irq(&real_tty->ctrl.lock);
526 : return retval;
527 : }
528 :
529 : /**
530 : * tiocgsid - get session id
531 : * @tty: tty passed by user
532 : * @real_tty: tty side of the tty passed by the user if a pty else the tty
533 : * @p: pointer to returned session id
534 : *
535 : * Obtain the session id of the tty. If there is no session
536 : * return an error.
537 : */
538 0 : static int tiocgsid(struct tty_struct *tty, struct tty_struct *real_tty, pid_t __user *p)
539 : {
540 : unsigned long flags;
541 : pid_t sid;
542 :
543 : /*
544 : * (tty == real_tty) is a cheap way of
545 : * testing if the tty is NOT a master pty.
546 : */
547 0 : if (tty == real_tty && current->signal->tty != real_tty)
548 : return -ENOTTY;
549 :
550 0 : spin_lock_irqsave(&real_tty->ctrl.lock, flags);
551 0 : if (!real_tty->ctrl.session)
552 : goto err;
553 0 : sid = pid_vnr(real_tty->ctrl.session);
554 0 : spin_unlock_irqrestore(&real_tty->ctrl.lock, flags);
555 :
556 0 : return put_user(sid, p);
557 :
558 : err:
559 0 : spin_unlock_irqrestore(&real_tty->ctrl.lock, flags);
560 0 : return -ENOTTY;
561 : }
562 :
563 : /*
564 : * Called from tty_ioctl(). If tty is a pty then real_tty is the slave side,
565 : * if not then tty == real_tty.
566 : */
567 0 : long tty_jobctrl_ioctl(struct tty_struct *tty, struct tty_struct *real_tty,
568 : struct file *file, unsigned int cmd, unsigned long arg)
569 : {
570 0 : void __user *p = (void __user *)arg;
571 :
572 0 : switch (cmd) {
573 : case TIOCNOTTY:
574 0 : if (current->signal->tty != tty)
575 : return -ENOTTY;
576 0 : no_tty();
577 0 : return 0;
578 : case TIOCSCTTY:
579 0 : return tiocsctty(real_tty, file, arg);
580 : case TIOCGPGRP:
581 0 : return tiocgpgrp(tty, real_tty, p);
582 : case TIOCSPGRP:
583 0 : return tiocspgrp(tty, real_tty, p);
584 : case TIOCGSID:
585 0 : return tiocgsid(tty, real_tty, p);
586 : }
587 : return -ENOIOCTLCMD;
588 : }
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