drivers/tty/tty_jobctrl.c

   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
  15 static int is_ignored(int sig)
  16 {
  17         return (sigismember(&current->blocked, sig) ||
  18                 current->sighand->action[sig-1].sa.sa_handler == SIG_IGN);
  19 }
  20
  21 /**
  22  *      tty_check_change        -       check for POSIX terminal changes
  23  *      @tty: tty to check
  24  *      @sig: signal to send
  25  *
  26  *      If we try to write to, or set the state of, a terminal and we're
  27  *      not in the foreground, send a SIGTTOU.  If the signal is blocked or
  28  *      ignored, go ahead and perform the operation.  (POSIX 7.2)
  29  *
  30  *      Locking: ctrl_lock
  31  */
  32 int __tty_check_change(struct tty_struct *tty, int sig)
  33 {
  34         unsigned long flags;
  35         struct pid *pgrp, *tty_pgrp;
  36         int ret = 0;
  37
  38         if (current->signal->tty != tty)
  39                 return 0;
  40
  41         rcu_read_lock();
  42         pgrp = task_pgrp(current);
  43
  44         spin_lock_irqsave(&tty->ctrl_lock, flags);
  45         tty_pgrp = tty->pgrp;
  46         spin_unlock_irqrestore(&tty->ctrl_lock, flags);
  47
  48         if (tty_pgrp && pgrp != tty_pgrp) {
  49                 if (is_ignored(sig)) {
  50                         if (sig == SIGTTIN)
  51                                 ret = -EIO;
  52                 } else if (is_current_pgrp_orphaned())
  53                         ret = -EIO;
  54                 else {
  55                         kill_pgrp(pgrp, sig, 1);
  56                         set_thread_flag(TIF_SIGPENDING);
  57                         ret = -ERESTARTSYS;
  58                 }
  59         }
  60         rcu_read_unlock();
  61
  62         if (!tty_pgrp)
  63                 tty_warn(tty, "sig=%d, tty->pgrp == NULL!\n", sig);
  64
  65         return ret;
  66 }
  67
  68 int tty_check_change(struct tty_struct *tty)
  69 {
  70         return __tty_check_change(tty, SIGTTOU);
  71 }
  72 EXPORT_SYMBOL(tty_check_change);
  73
  74 void proc_clear_tty(struct task_struct *p)
  75 {
  76         unsigned long flags;
  77         struct tty_struct *tty;
  78         spin_lock_irqsave(&p->sighand->siglock, flags);
  79         tty = p->signal->tty;
  80         p->signal->tty = NULL;
  81         spin_unlock_irqrestore(&p->sighand->siglock, flags);
  82         tty_kref_put(tty);
  83 }
  84
  85 /**
  86  * proc_set_tty -  set the controlling terminal
  87  *      @tty: tty structure
  88  *
  89  * Only callable by the session leader and only if it does not already have
  90  * a controlling terminal.
  91  *
  92  * Caller must hold:  tty_lock()
  93  *                    a readlock on tasklist_lock
  94  *                    sighand lock
  95  */
  96 static void __proc_set_tty(struct tty_struct *tty)
  97 {
  98         unsigned long flags;
  99
 100         spin_lock_irqsave(&tty->ctrl_lock, flags);
 101         /*
 102          * The session and fg pgrp references will be non-NULL if
 103          * tiocsctty() is stealing the controlling tty
 104          */
 105         put_pid(tty->session);
 106         put_pid(tty->pgrp);
 107         tty->pgrp = get_pid(task_pgrp(current));
 108         tty->session = get_pid(task_session(current));
 109         spin_unlock_irqrestore(&tty->ctrl_lock, flags);
 110         if (current->signal->tty) {
 111                 tty_debug(tty, "current tty %s not NULL!!\n",
 112                           current->signal->tty->name);
 113                 tty_kref_put(current->signal->tty);
 114         }
 115         put_pid(current->signal->tty_old_pgrp);
 116         current->signal->tty = tty_kref_get(tty);
 117         current->signal->tty_old_pgrp = NULL;
 118 }
 119
 120 static void proc_set_tty(struct tty_struct *tty)
 121 {
 122         spin_lock_irq(&current->sighand->siglock);
 123         __proc_set_tty(tty);
 124         spin_unlock_irq(&current->sighand->siglock);
 125 }
 126
 127 /*
 128  * Called by tty_open() to set the controlling tty if applicable.
 129  */
 130 void tty_open_proc_set_tty(struct file *filp, struct tty_struct *tty)
 131 {
 132         read_lock(&tasklist_lock);
 133         spin_lock_irq(&current->sighand->siglock);
 134         if (current->signal->leader &&
 135             !current->signal->tty &&
 136             tty->session == NULL) {
 137                 /*
 138                  * Don't let a process that only has write access to the tty
 139                  * obtain the privileges associated with having a tty as
 140                  * controlling terminal (being able to reopen it with full
 141                  * access through /dev/tty, being able to perform pushback).
 142                  * Many distributions set the group of all ttys to "tty" and
 143                  * grant write-only access to all terminals for setgid tty
 144                  * binaries, which should not imply full privileges on all ttys.
 145                  *
 146                  * This could theoretically break old code that performs open()
 147                  * on a write-only file descriptor. In that case, it might be
 148                  * necessary to also permit this if
 149                  * inode_permission(inode, MAY_READ) == 0.
 150                  */
 151                 if (filp->f_mode & FMODE_READ)
 152                         __proc_set_tty(tty);
 153         }
 154         spin_unlock_irq(&current->sighand->siglock);
 155         read_unlock(&tasklist_lock);
 156 }
 157
 158 struct tty_struct *get_current_tty(void)
 159 {
 160         struct tty_struct *tty;
 161         unsigned long flags;
 162
 163         spin_lock_irqsave(&current->sighand->siglock, flags);
 164         tty = tty_kref_get(current->signal->tty);
 165         spin_unlock_irqrestore(&current->sighand->siglock, flags);
 166         return tty;
 167 }
 168 EXPORT_SYMBOL_GPL(get_current_tty);
 169
 170 /*
 171  * Called from tty_release().
 172  */
 173 void session_clear_tty(struct pid *session)
 174 {
 175         struct task_struct *p;
 176         do_each_pid_task(session, PIDTYPE_SID, p) {
 177                 proc_clear_tty(p);
 178         } while_each_pid_task(session, PIDTYPE_SID, p);
 179 }
 180
 181 /**
 182  *      tty_signal_session_leader       - sends SIGHUP to session leader
 183  *      @tty: controlling tty
 184  *      @exit_session: if non-zero, signal all foreground group processes
 185  *
 186  *      Send SIGHUP and SIGCONT to the session leader and its process group.
 187  *      Optionally, signal all processes in the foreground process group.
 188  *
 189  *      Returns the number of processes in the session with this tty
 190  *      as their controlling terminal. This value is used to drop
 191  *      tty references for those processes.
 192  */
 193 int tty_signal_session_leader(struct tty_struct *tty, int exit_session)
 194 {
 195         struct task_struct *p;
 196         int refs = 0;
 197         struct pid *tty_pgrp = NULL;
 198
 199         read_lock(&tasklist_lock);
 200         if (tty->session) {
 201                 do_each_pid_task(tty->session, PIDTYPE_SID, p) {
 202                         spin_lock_irq(&p->sighand->siglock);
 203                         if (p->signal->tty == tty) {
 204                                 p->signal->tty = NULL;
 205                                 /* We defer the dereferences outside fo
 206                                    the tasklist lock */
 207                                 refs++;
 208                         }
 209                         if (!p->signal->leader) {
 210                                 spin_unlock_irq(&p->sighand->siglock);
 211                                 continue;
 212                         }
 213                         __group_send_sig_info(SIGHUP, SEND_SIG_PRIV, p);
 214                         __group_send_sig_info(SIGCONT, SEND_SIG_PRIV, p);
 215                         put_pid(p->signal->tty_old_pgrp);  /* A noop */
 216                         spin_lock(&tty->ctrl_lock);
 217                         tty_pgrp = get_pid(tty->pgrp);
 218                         if (tty->pgrp)
 219                                 p->signal->tty_old_pgrp = get_pid(tty->pgrp);
 220                         spin_unlock(&tty->ctrl_lock);
 221                         spin_unlock_irq(&p->sighand->siglock);
 222                 } while_each_pid_task(tty->session, PIDTYPE_SID, p);
 223         }
 224         read_unlock(&tasklist_lock);
 225
 226         if (tty_pgrp) {
 227                 if (exit_session)
 228                         kill_pgrp(tty_pgrp, SIGHUP, exit_session);
 229                 put_pid(tty_pgrp);
 230         }
 231
 232         return refs;
 233 }
 234
 235 /**
 236  *      disassociate_ctty       -       disconnect controlling tty
 237  *      @on_exit: true if exiting so need to "hang up" the session
 238  *
 239  *      This function is typically called only by the session leader, when
 240  *      it wants to disassociate itself from its controlling tty.
 241  *
 242  *      It performs the following functions:
 243  *      (1)  Sends a SIGHUP and SIGCONT to the foreground process group
 244  *      (2)  Clears the tty from being controlling the session
 245  *      (3)  Clears the controlling tty for all processes in the
 246  *              session group.
 247  *
 248  *      The argument on_exit is set to 1 if called when a process is
 249  *      exiting; it is 0 if called by the ioctl TIOCNOTTY.
 250  *
 251  *      Locking:
 252  *              BTM is taken for hysterical raisons, and held when
 253  *                called from no_tty().
 254  *                tty_mutex is taken to protect tty
 255  *                ->siglock is taken to protect ->signal/->sighand
 256  *                tasklist_lock is taken to walk process list for sessions
 257  *                  ->siglock is taken to protect ->signal/->sighand
 258  */
 259 void disassociate_ctty(int on_exit)
 260 {
 261         struct tty_struct *tty;
 262
 263         if (!current->signal->leader)
 264                 return;
 265
 266         tty = get_current_tty();
 267         if (tty) {
 268                 if (on_exit && tty->driver->type != TTY_DRIVER_TYPE_PTY) {
 269                         tty_vhangup_session(tty);
 270                 } else {
 271                         struct pid *tty_pgrp = tty_get_pgrp(tty);
 272                         if (tty_pgrp) {
 273                                 kill_pgrp(tty_pgrp, SIGHUP, on_exit);
 274                                 if (!on_exit)
 275                                         kill_pgrp(tty_pgrp, SIGCONT, on_exit);
 276                                 put_pid(tty_pgrp);
 277                         }
 278                 }
 279                 tty_kref_put(tty);
 280
 281         } else if (on_exit) {
 282                 struct pid *old_pgrp;
 283                 spin_lock_irq(&current->sighand->siglock);
 284                 old_pgrp = current->signal->tty_old_pgrp;
 285                 current->signal->tty_old_pgrp = NULL;
 286                 spin_unlock_irq(&current->sighand->siglock);
 287                 if (old_pgrp) {
 288                         kill_pgrp(old_pgrp, SIGHUP, on_exit);
 289                         kill_pgrp(old_pgrp, SIGCONT, on_exit);
 290                         put_pid(old_pgrp);
 291                 }
 292                 return;
 293         }
 294
 295         spin_lock_irq(&current->sighand->siglock);
 296         put_pid(current->signal->tty_old_pgrp);
 297         current->signal->tty_old_pgrp = NULL;
 298         tty = tty_kref_get(current->signal->tty);
 299         spin_unlock_irq(&current->sighand->siglock);
 300
 301         if (tty) {
 302                 unsigned long flags;
 303
 304                 tty_lock(tty);
 305                 spin_lock_irqsave(&tty->ctrl_lock, flags);
 306                 put_pid(tty->session);
 307                 put_pid(tty->pgrp);
 308                 tty->session = NULL;
 309                 tty->pgrp = NULL;
 310                 spin_unlock_irqrestore(&tty->ctrl_lock, flags);
 311                 tty_unlock(tty);
 312                 tty_kref_put(tty);
 313         }
 314
 315         /* Now clear signal->tty under the lock */
 316         read_lock(&tasklist_lock);
 317         session_clear_tty(task_session(current));
 318         read_unlock(&tasklist_lock);
 319 }
 320
 321 /*
 322  *
 323  *      no_tty  - Ensure the current process does not have a controlling tty
 324  */
 325 void no_tty(void)
 326 {
 327         /* FIXME: Review locking here. The tty_lock never covered any race
 328            between a new association and proc_clear_tty but possible we need
 329            to protect against this anyway */
 330         struct task_struct *tsk = current;
 331         disassociate_ctty(0);
 332         proc_clear_tty(tsk);
 333 }
 334
 335 /**
 336  *      tiocsctty       -       set controlling tty
 337  *      @tty: tty structure
 338  *      @file: file structure used to check permissions
 339  *      @arg: user argument
 340  *
 341  *      This ioctl is used to manage job control. It permits a session
 342  *      leader to set this tty as the controlling tty for the session.
 343  *
 344  *      Locking:
 345  *              Takes tty_lock() to serialize proc_set_tty() for this tty
 346  *              Takes tasklist_lock internally to walk sessions
 347  *              Takes ->siglock() when updating signal->tty
 348  */
 349 static int tiocsctty(struct tty_struct *tty, struct file *file, int arg)
 350 {
 351         int ret = 0;
 352
 353         tty_lock(tty);
 354         read_lock(&tasklist_lock);
 355
 356         if (current->signal->leader && (task_session(current) == tty->session))
 357                 goto unlock;
 358
 359         /*
 360          * The process must be a session leader and
 361          * not have a controlling tty already.
 362          */
 363         if (!current->signal->leader || current->signal->tty) {
 364                 ret = -EPERM;
 365                 goto unlock;
 366         }
 367
 368         if (tty->session) {
 369                 /*
 370                  * This tty is already the controlling
 371                  * tty for another session group!
 372                  */
 373                 if (arg == 1 && capable(CAP_SYS_ADMIN)) {
 374                         /*
 375                          * Steal it away
 376                          */
 377                         session_clear_tty(tty->session);
 378                 } else {
 379                         ret = -EPERM;
 380                         goto unlock;
 381                 }
 382         }
 383
 384         /* See the comment in tty_open_proc_set_tty(). */
 385         if ((file->f_mode & FMODE_READ) == 0 && !capable(CAP_SYS_ADMIN)) {
 386                 ret = -EPERM;
 387                 goto unlock;
 388         }
 389
 390         proc_set_tty(tty);
 391 unlock:
 392         read_unlock(&tasklist_lock);
 393         tty_unlock(tty);
 394         return ret;
 395 }
 396
 397 /**
 398  *      tty_get_pgrp    -       return a ref counted pgrp pid
 399  *      @tty: tty to read
 400  *
 401  *      Returns a refcounted instance of the pid struct for the process
 402  *      group controlling the tty.
 403  */
 404 struct pid *tty_get_pgrp(struct tty_struct *tty)
 405 {
 406         unsigned long flags;
 407         struct pid *pgrp;
 408
 409         spin_lock_irqsave(&tty->ctrl_lock, flags);
 410         pgrp = get_pid(tty->pgrp);
 411         spin_unlock_irqrestore(&tty->ctrl_lock, flags);
 412
 413         return pgrp;
 414 }
 415 EXPORT_SYMBOL_GPL(tty_get_pgrp);
 416
 417 /*
 418  * This checks not only the pgrp, but falls back on the pid if no
 419  * satisfactory pgrp is found. I dunno - gdb doesn't work correctly
 420  * without this...
 421  *
 422  * The caller must hold rcu lock or the tasklist lock.
 423  */
 424 static struct pid *session_of_pgrp(struct pid *pgrp)
 425 {
 426         struct task_struct *p;
 427         struct pid *sid = NULL;
 428
 429         p = pid_task(pgrp, PIDTYPE_PGID);
 430         if (p == NULL)
 431                 p = pid_task(pgrp, PIDTYPE_PID);
 432         if (p != NULL)
 433                 sid = task_session(p);
 434
 435         return sid;
 436 }
 437
 438 /**
 439  *      tiocgpgrp               -       get process group
 440  *      @tty: tty passed by user
 441  *      @real_tty: tty side of the tty passed by the user if a pty else the tty
 442  *      @p: returned pid
 443  *
 444  *      Obtain the process group of the tty. If there is no process group
 445  *      return an error.
 446  *
 447  *      Locking: none. Reference to current->signal->tty is safe.
 448  */
 449 static int tiocgpgrp(struct tty_struct *tty, struct tty_struct *real_tty, pid_t __user *p)
 450 {
 451         struct pid *pid;
 452         int ret;
 453         /*
 454          * (tty == real_tty) is a cheap way of
 455          * testing if the tty is NOT a master pty.
 456          */
 457         if (tty == real_tty && current->signal->tty != real_tty)
 458                 return -ENOTTY;
 459         pid = tty_get_pgrp(real_tty);
 460         ret =  put_user(pid_vnr(pid), p);
 461         put_pid(pid);
 462         return ret;
 463 }
 464
 465 /**
 466  *      tiocspgrp               -       attempt to set process group
 467  *      @tty: tty passed by user
 468  *      @real_tty: tty side device matching tty passed by user
 469  *      @p: pid pointer
 470  *
 471  *      Set the process group of the tty to the session passed. Only
 472  *      permitted where the tty session is our session.
 473  *
 474  *      Locking: RCU, ctrl lock
 475  */
 476 static int tiocspgrp(struct tty_struct *tty, struct tty_struct *real_tty, pid_t __user *p)
 477 {
 478         struct pid *pgrp;
 479         pid_t pgrp_nr;
 480         int retval = tty_check_change(real_tty);
 481
 482         if (retval == -EIO)
 483                 return -ENOTTY;
 484         if (retval)
 485                 return retval;
 486
 487         if (get_user(pgrp_nr, p))
 488                 return -EFAULT;
 489         if (pgrp_nr < 0)
 490                 return -EINVAL;
 491
 492         spin_lock_irq(&real_tty->ctrl_lock);
 493         if (!current->signal->tty ||
 494             (current->signal->tty != real_tty) ||
 495             (real_tty->session != task_session(current))) {
 496                 retval = -ENOTTY;
 497                 goto out_unlock_ctrl;
 498         }
 499         rcu_read_lock();
 500         pgrp = find_vpid(pgrp_nr);
 501         retval = -ESRCH;
 502         if (!pgrp)
 503                 goto out_unlock;
 504         retval = -EPERM;
 505         if (session_of_pgrp(pgrp) != task_session(current))
 506                 goto out_unlock;
 507         retval = 0;
 508         put_pid(real_tty->pgrp);
 509         real_tty->pgrp = get_pid(pgrp);
 510 out_unlock:
 511         rcu_read_unlock();
 512 out_unlock_ctrl:
 513         spin_unlock_irq(&real_tty->ctrl_lock);
 514         return retval;
 515 }
 516
 517 /**
 518  *      tiocgsid                -       get session id
 519  *      @tty: tty passed by user
 520  *      @real_tty: tty side of the tty passed by the user if a pty else the tty
 521  *      @p: pointer to returned session id
 522  *
 523  *      Obtain the session id of the tty. If there is no session
 524  *      return an error.
 525  */
 526 static int tiocgsid(struct tty_struct *tty, struct tty_struct *real_tty, pid_t __user *p)
 527 {
 528         unsigned long flags;
 529         pid_t sid;
 530
 531         /*
 532          * (tty == real_tty) is a cheap way of
 533          * testing if the tty is NOT a master pty.
 534         */
 535         if (tty == real_tty && current->signal->tty != real_tty)
 536                 return -ENOTTY;
 537
 538         spin_lock_irqsave(&real_tty->ctrl_lock, flags);
 539         if (!real_tty->session)
 540                 goto err;
 541         sid = pid_vnr(real_tty->session);
 542         spin_unlock_irqrestore(&real_tty->ctrl_lock, flags);
 543
 544         return put_user(sid, p);
 545
 546 err:
 547         spin_unlock_irqrestore(&real_tty->ctrl_lock, flags);
 548         return -ENOTTY;
 549 }
 550
 551 /*
 552  * Called from tty_ioctl(). If tty is a pty then real_tty is the slave side,
 553  * if not then tty == real_tty.
 554  */
 555 long tty_jobctrl_ioctl(struct tty_struct *tty, struct tty_struct *real_tty,
 556                        struct file *file, unsigned int cmd, unsigned long arg)
 557 {
 558         void __user *p = (void __user *)arg;
 559
 560         switch (cmd) {
 561         case TIOCNOTTY:
 562                 if (current->signal->tty != tty)
 563                         return -ENOTTY;
 564                 no_tty();
 565                 return 0;
 566         case TIOCSCTTY:
 567                 return tiocsctty(real_tty, file, arg);
 568         case TIOCGPGRP:
 569                 return tiocgpgrp(tty, real_tty, p);
 570         case TIOCSPGRP:
 571                 return tiocspgrp(tty, real_tty, p);
 572         case TIOCGSID:
 573                 return tiocgsid(tty, real_tty, p);
 574         }
 575         return -ENOIOCTLCMD;
 576 }