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 #include "tty.h"
  15
  16 static int is_ignored(int sig)
  17 {
  18         return (sigismember(&current->blocked, sig) ||
  19                 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 int __tty_check_change(struct tty_struct *tty, int sig)
  34 {
  35         unsigned long flags;
  36         struct pid *pgrp, *tty_pgrp;
  37         int ret = 0;
  38
  39         if (current->signal->tty != tty)
  40                 return 0;
  41
  42         rcu_read_lock();
  43         pgrp = task_pgrp(current);
  44
  45         spin_lock_irqsave(&tty->ctrl.lock, flags);
  46         tty_pgrp = tty->ctrl.pgrp;
  47         spin_unlock_irqrestore(&tty->ctrl.lock, flags);
  48
  49         if (tty_pgrp && pgrp != tty_pgrp) {
  50                 if (is_ignored(sig)) {
  51                         if (sig == SIGTTIN)
  52                                 ret = -EIO;
  53                 } else if (is_current_pgrp_orphaned())
  54                         ret = -EIO;
  55                 else {
  56                         kill_pgrp(pgrp, sig, 1);
  57                         set_thread_flag(TIF_SIGPENDING);
  58                         ret = -ERESTARTSYS;
  59                 }
  60         }
  61         rcu_read_unlock();
  62
  63         if (!tty_pgrp)
  64                 tty_warn(tty, "sig=%d, tty->pgrp == NULL!\n", sig);
  65
  66         return ret;
  67 }
  68
  69 int tty_check_change(struct tty_struct *tty)
  70 {
  71         return __tty_check_change(tty, SIGTTOU);
  72 }
  73 EXPORT_SYMBOL(tty_check_change);
  74
  75 void proc_clear_tty(struct task_struct *p)
  76 {
  77         unsigned long flags;
  78         struct tty_struct *tty;
  79
  80         spin_lock_irqsave(&p->sighand->siglock, flags);
  81         tty = p->signal->tty;
  82         p->signal->tty = NULL;
  83         spin_unlock_irqrestore(&p->sighand->siglock, flags);
  84         tty_kref_put(tty);
  85 }
  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 static void __proc_set_tty(struct tty_struct *tty)
  99 {
 100         unsigned long flags;
 101
 102         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         put_pid(tty->ctrl.session);
 108         put_pid(tty->ctrl.pgrp);
 109         tty->ctrl.pgrp = get_pid(task_pgrp(current));
 110         tty->ctrl.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);
 116         }
 117         put_pid(current->signal->tty_old_pgrp);
 118         current->signal->tty = tty_kref_get(tty);
 119         current->signal->tty_old_pgrp = NULL;
 120 }
 121
 122 static void proc_set_tty(struct tty_struct *tty)
 123 {
 124         spin_lock_irq(&current->sighand->siglock);
 125         __proc_set_tty(tty);
 126         spin_unlock_irq(&current->sighand->siglock);
 127 }
 128
 129 /*
 130  * Called by tty_open() to set the controlling tty if applicable.
 131  */
 132 void tty_open_proc_set_tty(struct file *filp, struct tty_struct *tty)
 133 {
 134         read_lock(&tasklist_lock);
 135         spin_lock_irq(&current->sighand->siglock);
 136         if (current->signal->leader &&
 137             !current->signal->tty &&
 138             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                 if (filp->f_mode & FMODE_READ)
 154                         __proc_set_tty(tty);
 155         }
 156         spin_unlock_irq(&current->sighand->siglock);
 157         read_unlock(&tasklist_lock);
 158 }
 159
 160 struct tty_struct *get_current_tty(void)
 161 {
 162         struct tty_struct *tty;
 163         unsigned long flags;
 164
 165         spin_lock_irqsave(&current->sighand->siglock, flags);
 166         tty = tty_kref_get(current->signal->tty);
 167         spin_unlock_irqrestore(&current->sighand->siglock, flags);
 168         return tty;
 169 }
 170 EXPORT_SYMBOL_GPL(get_current_tty);
 171
 172 /*
 173  * Called from tty_release().
 174  */
 175 void session_clear_tty(struct pid *session)
 176 {
 177         struct task_struct *p;
 178
 179         do_each_pid_task(session, PIDTYPE_SID, p) {
 180                 proc_clear_tty(p);
 181         } while_each_pid_task(session, PIDTYPE_SID, p);
 182 }
 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 int tty_signal_session_leader(struct tty_struct *tty, int exit_session)
 197 {
 198         struct task_struct *p;
 199         int refs = 0;
 200         struct pid *tty_pgrp = NULL;
 201
 202         read_lock(&tasklist_lock);
 203         if (tty->ctrl.session) {
 204                 do_each_pid_task(tty->ctrl.session, PIDTYPE_SID, p) {
 205                         spin_lock_irq(&p->sighand->siglock);
 206                         if (p->signal->tty == tty) {
 207                                 p->signal->tty = NULL;
 208                                 /*
 209                                  * We defer the dereferences outside of
 210                                  * the tasklist lock.
 211                                  */
 212                                 refs++;
 213                         }
 214                         if (!p->signal->leader) {
 215                                 spin_unlock_irq(&p->sighand->siglock);
 216                                 continue;
 217                         }
 218                         send_signal_locked(SIGHUP, SEND_SIG_PRIV, p, PIDTYPE_TGID);
 219                         send_signal_locked(SIGCONT, SEND_SIG_PRIV, p, PIDTYPE_TGID);
 220                         put_pid(p->signal->tty_old_pgrp);  /* A noop */
 221                         spin_lock(&tty->ctrl.lock);
 222                         tty_pgrp = get_pid(tty->ctrl.pgrp);
 223                         if (tty->ctrl.pgrp)
 224                                 p->signal->tty_old_pgrp =
 225                                         get_pid(tty->ctrl.pgrp);
 226                         spin_unlock(&tty->ctrl.lock);
 227                         spin_unlock_irq(&p->sighand->siglock);
 228                 } while_each_pid_task(tty->ctrl.session, PIDTYPE_SID, p);
 229         }
 230         read_unlock(&tasklist_lock);
 231
 232         if (tty_pgrp) {
 233                 if (exit_session)
 234                         kill_pgrp(tty_pgrp, SIGHUP, exit_session);
 235                 put_pid(tty_pgrp);
 236         }
 237
 238         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 void disassociate_ctty(int on_exit)
 266 {
 267         struct tty_struct *tty;
 268
 269         if (!current->signal->leader)
 270                 return;
 271
 272         tty = get_current_tty();
 273         if (tty) {
 274                 if (on_exit && tty->driver->type != TTY_DRIVER_TYPE_PTY) {
 275                         tty_vhangup_session(tty);
 276                 } else {
 277                         struct pid *tty_pgrp = tty_get_pgrp(tty);
 278
 279                         if (tty_pgrp) {
 280                                 kill_pgrp(tty_pgrp, SIGHUP, on_exit);
 281                                 if (!on_exit)
 282                                         kill_pgrp(tty_pgrp, SIGCONT, on_exit);
 283                                 put_pid(tty_pgrp);
 284                         }
 285                 }
 286                 tty_kref_put(tty);
 287
 288         } else if (on_exit) {
 289                 struct pid *old_pgrp;
 290
 291                 spin_lock_irq(&current->sighand->siglock);
 292                 old_pgrp = current->signal->tty_old_pgrp;
 293                 current->signal->tty_old_pgrp = NULL;
 294                 spin_unlock_irq(&current->sighand->siglock);
 295                 if (old_pgrp) {
 296                         kill_pgrp(old_pgrp, SIGHUP, on_exit);
 297                         kill_pgrp(old_pgrp, SIGCONT, on_exit);
 298                         put_pid(old_pgrp);
 299                 }
 300                 return;
 301         }
 302
 303         spin_lock_irq(&current->sighand->siglock);
 304         put_pid(current->signal->tty_old_pgrp);
 305         current->signal->tty_old_pgrp = NULL;
 306         tty = tty_kref_get(current->signal->tty);
 307         spin_unlock_irq(&current->sighand->siglock);
 308
 309         if (tty) {
 310                 unsigned long flags;
 311
 312                 tty_lock(tty);
 313                 spin_lock_irqsave(&tty->ctrl.lock, flags);
 314                 put_pid(tty->ctrl.session);
 315                 put_pid(tty->ctrl.pgrp);
 316                 tty->ctrl.session = NULL;
 317                 tty->ctrl.pgrp = NULL;
 318                 spin_unlock_irqrestore(&tty->ctrl.lock, flags);
 319                 tty_unlock(tty);
 320                 tty_kref_put(tty);
 321         }
 322
 323         /* Now clear signal->tty under the lock */
 324         read_lock(&tasklist_lock);
 325         session_clear_tty(task_session(current));
 326         read_unlock(&tasklist_lock);
 327 }
 328
 329 /*
 330  *
 331  *      no_tty  - Ensure the current process does not have a controlling tty
 332  */
 333 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         struct task_struct *tsk = current;
 341
 342         disassociate_ctty(0);
 343         proc_clear_tty(tsk);
 344 }
 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 static int tiocsctty(struct tty_struct *tty, struct file *file, int arg)
 361 {
 362         int ret = 0;
 363
 364         tty_lock(tty);
 365         read_lock(&tasklist_lock);
 366
 367         if (current->signal->leader &&
 368                         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         if (!current->signal->leader || current->signal->tty) {
 376                 ret = -EPERM;
 377                 goto unlock;
 378         }
 379
 380         if (tty->ctrl.session) {
 381                 /*
 382                  * This tty is already the controlling
 383                  * tty for another session group!
 384                  */
 385                 if (arg == 1 && capable(CAP_SYS_ADMIN)) {
 386                         /*
 387                          * Steal it away
 388                          */
 389                         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         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         read_unlock(&tasklist_lock);
 405         tty_unlock(tty);
 406         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 struct pid *tty_get_pgrp(struct tty_struct *tty)
 417 {
 418         unsigned long flags;
 419         struct pid *pgrp;
 420
 421         spin_lock_irqsave(&tty->ctrl.lock, flags);
 422         pgrp = get_pid(tty->ctrl.pgrp);
 423         spin_unlock_irqrestore(&tty->ctrl.lock, flags);
 424
 425         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 static struct pid *session_of_pgrp(struct pid *pgrp)
 437 {
 438         struct task_struct *p;
 439         struct pid *sid = NULL;
 440
 441         p = pid_task(pgrp, PIDTYPE_PGID);
 442         if (p == NULL)
 443                 p = pid_task(pgrp, PIDTYPE_PID);
 444         if (p != NULL)
 445                 sid = task_session(p);
 446
 447         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 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         if (tty == real_tty && current->signal->tty != real_tty)
 470                 return -ENOTTY;
 471         pid = tty_get_pgrp(real_tty);
 472         ret =  put_user(pid_vnr(pid), p);
 473         put_pid(pid);
 474         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 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         int retval = tty_check_change(real_tty);
 493
 494         if (retval == -EIO)
 495                 return -ENOTTY;
 496         if (retval)
 497                 return retval;
 498
 499         if (get_user(pgrp_nr, p))
 500                 return -EFAULT;
 501         if (pgrp_nr < 0)
 502                 return -EINVAL;
 503
 504         spin_lock_irq(&real_tty->ctrl.lock);
 505         if (!current->signal->tty ||
 506             (current->signal->tty != real_tty) ||
 507             (real_tty->ctrl.session != task_session(current))) {
 508                 retval = -ENOTTY;
 509                 goto out_unlock_ctrl;
 510         }
 511         rcu_read_lock();
 512         pgrp = find_vpid(pgrp_nr);
 513         retval = -ESRCH;
 514         if (!pgrp)
 515                 goto out_unlock;
 516         retval = -EPERM;
 517         if (session_of_pgrp(pgrp) != task_session(current))
 518                 goto out_unlock;
 519         retval = 0;
 520         put_pid(real_tty->ctrl.pgrp);
 521         real_tty->ctrl.pgrp = get_pid(pgrp);
 522 out_unlock:
 523         rcu_read_unlock();
 524 out_unlock_ctrl:
 525         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 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         if (tty == real_tty && current->signal->tty != real_tty)
 548                 return -ENOTTY;
 549
 550         spin_lock_irqsave(&real_tty->ctrl.lock, flags);
 551         if (!real_tty->ctrl.session)
 552                 goto err;
 553         sid = pid_vnr(real_tty->ctrl.session);
 554         spin_unlock_irqrestore(&real_tty->ctrl.lock, flags);
 555
 556         return put_user(sid, p);
 557
 558 err:
 559         spin_unlock_irqrestore(&real_tty->ctrl.lock, flags);
 560         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 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         void __user *p = (void __user *)arg;
 571
 572         switch (cmd) {
 573         case TIOCNOTTY:
 574                 if (current->signal->tty != tty)
 575                         return -ENOTTY;
 576                 no_tty();
 577                 return 0;
 578         case TIOCSCTTY:
 579                 return tiocsctty(real_tty, file, arg);
 580         case TIOCGPGRP:
 581                 return tiocgpgrp(tty, real_tty, p);
 582         case TIOCSPGRP:
 583                 return tiocspgrp(tty, real_tty, p);
 584         case TIOCGSID:
 585                 return tiocgsid(tty, real_tty, p);
 586         }
 587         return -ENOIOCTLCMD;
 588 }