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->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->session);
 108         put_pid(tty->pgrp);
 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);
 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->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->session) {
 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;
 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                         __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);
 223                         if (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);
 228         }
 229         read_unlock(&tasklist_lock);
 230
 231         if (tty_pgrp) {
 232                 if (exit_session)
 233                         kill_pgrp(tty_pgrp, SIGHUP, exit_session);
 234                 put_pid(tty_pgrp);
 235         }
 236
 237         return refs;
 238 }
 239
 240 /**
 241  *      disassociate_ctty       -       disconnect controlling tty
 242  *      @on_exit: true if exiting so need to "hang up" the session
 243  *
 244  *      This function is typically called only by the session leader, when
 245  *      it wants to disassociate itself from its controlling tty.
 246  *
 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
 251  *              session group.
 252  *
 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.
 255  *
 256  *      Locking:
 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
 263  */
 264 void disassociate_ctty(int on_exit)
 265 {
 266         struct tty_struct *tty;
 267
 268         if (!current->signal->leader)
 269                 return;
 270
 271         tty = get_current_tty();
 272         if (tty) {
 273                 if (on_exit && tty->driver->type != TTY_DRIVER_TYPE_PTY) {
 274                         tty_vhangup_session(tty);
 275                 } else {
 276                         struct pid *tty_pgrp = tty_get_pgrp(tty);
 277
 278                         if (tty_pgrp) {
 279                                 kill_pgrp(tty_pgrp, SIGHUP, on_exit);
 280                                 if (!on_exit)
 281                                         kill_pgrp(tty_pgrp, SIGCONT, on_exit);
 282                                 put_pid(tty_pgrp);
 283                         }
 284                 }
 285                 tty_kref_put(tty);
 286
 287         } else if (on_exit) {
 288                 struct pid *old_pgrp;
 289
 290                 spin_lock_irq(&current->sighand->siglock);
 291                 old_pgrp = current->signal->tty_old_pgrp;
 292                 current->signal->tty_old_pgrp = NULL;
 293                 spin_unlock_irq(&current->sighand->siglock);
 294                 if (old_pgrp) {
 295                         kill_pgrp(old_pgrp, SIGHUP, on_exit);
 296                         kill_pgrp(old_pgrp, SIGCONT, on_exit);
 297                         put_pid(old_pgrp);
 298                 }
 299                 return;
 300         }
 301
 302         spin_lock_irq(&current->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(&current->sighand->siglock);
 307
 308         if (tty) {
 309                 unsigned long flags;
 310
 311                 tty_lock(tty);
 312                 spin_lock_irqsave(&tty->ctrl_lock, flags);
 313                 put_pid(tty->session);
 314                 put_pid(tty->pgrp);
 315                 tty->session = NULL;
 316                 tty->pgrp = NULL;
 317                 spin_unlock_irqrestore(&tty->ctrl_lock, flags);
 318                 tty_unlock(tty);
 319                 tty_kref_put(tty);
 320         }
 321
 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);
 326 }
 327
 328 /*
 329  *
 330  *      no_tty  - Ensure the current process does not have a controlling tty
 331  */
 332 void no_tty(void)
 333 {
 334         /*
 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.
 338          */
 339         struct task_struct *tsk = current;
 340
 341         disassociate_ctty(0);
 342         proc_clear_tty(tsk);
 343 }
 344
 345 /**
 346  *      tiocsctty       -       set controlling tty
 347  *      @tty: tty structure
 348  *      @file: file structure used to check permissions
 349  *      @arg: user argument
 350  *
 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.
 353  *
 354  *      Locking:
 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
 358  */
 359 static int tiocsctty(struct tty_struct *tty, struct file *file, int arg)
 360 {
 361         int ret = 0;
 362
 363         tty_lock(tty);
 364         read_lock(&tasklist_lock);
 365
 366         if (current->signal->leader && (task_session(current) == tty->session))
 367                 goto unlock;
 368
 369         /*
 370          * The process must be a session leader and
 371          * not have a controlling tty already.
 372          */
 373         if (!current->signal->leader || current->signal->tty) {
 374                 ret = -EPERM;
 375                 goto unlock;
 376         }
 377
 378         if (tty->session) {
 379                 /*
 380                  * This tty is already the controlling
 381                  * tty for another session group!
 382                  */
 383                 if (arg == 1 && capable(CAP_SYS_ADMIN)) {
 384                         /*
 385                          * Steal it away
 386                          */
 387                         session_clear_tty(tty->session);
 388                 } else {
 389                         ret = -EPERM;
 390                         goto unlock;
 391                 }
 392         }
 393
 394         /* See the comment in tty_open_proc_set_tty(). */
 395         if ((file->f_mode & FMODE_READ) == 0 && !capable(CAP_SYS_ADMIN)) {
 396                 ret = -EPERM;
 397                 goto unlock;
 398         }
 399
 400         proc_set_tty(tty);
 401 unlock:
 402         read_unlock(&tasklist_lock);
 403         tty_unlock(tty);
 404         return ret;
 405 }
 406
 407 /**
 408  *      tty_get_pgrp    -       return a ref counted pgrp pid
 409  *      @tty: tty to read
 410  *
 411  *      Returns a refcounted instance of the pid struct for the process
 412  *      group controlling the tty.
 413  */
 414 struct pid *tty_get_pgrp(struct tty_struct *tty)
 415 {
 416         unsigned long flags;
 417         struct pid *pgrp;
 418
 419         spin_lock_irqsave(&tty->ctrl_lock, flags);
 420         pgrp = get_pid(tty->pgrp);
 421         spin_unlock_irqrestore(&tty->ctrl_lock, flags);
 422
 423         return pgrp;
 424 }
 425 EXPORT_SYMBOL_GPL(tty_get_pgrp);
 426
 427 /*
 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
 430  * without this...
 431  *
 432  * The caller must hold rcu lock or the tasklist lock.
 433  */
 434 static struct pid *session_of_pgrp(struct pid *pgrp)
 435 {
 436         struct task_struct *p;
 437         struct pid *sid = NULL;
 438
 439         p = pid_task(pgrp, PIDTYPE_PGID);
 440         if (p == NULL)
 441                 p = pid_task(pgrp, PIDTYPE_PID);
 442         if (p != NULL)
 443                 sid = task_session(p);
 444
 445         return sid;
 446 }
 447
 448 /**
 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
 452  *      @p: returned pid
 453  *
 454  *      Obtain the process group of the tty. If there is no process group
 455  *      return an error.
 456  *
 457  *      Locking: none. Reference to current->signal->tty is safe.
 458  */
 459 static int tiocgpgrp(struct tty_struct *tty, struct tty_struct *real_tty, pid_t __user *p)
 460 {
 461         struct pid *pid;
 462         int ret;
 463         /*
 464          * (tty == real_tty) is a cheap way of
 465          * testing if the tty is NOT a master pty.
 466          */
 467         if (tty == real_tty && current->signal->tty != real_tty)
 468                 return -ENOTTY;
 469         pid = tty_get_pgrp(real_tty);
 470         ret =  put_user(pid_vnr(pid), p);
 471         put_pid(pid);
 472         return ret;
 473 }
 474
 475 /**
 476  *      tiocspgrp               -       attempt to set process group
 477  *      @tty: tty passed by user
 478  *      @real_tty: tty side device matching tty passed by user
 479  *      @p: pid pointer
 480  *
 481  *      Set the process group of the tty to the session passed. Only
 482  *      permitted where the tty session is our session.
 483  *
 484  *      Locking: RCU, ctrl lock
 485  */
 486 static int tiocspgrp(struct tty_struct *tty, struct tty_struct *real_tty, pid_t __user *p)
 487 {
 488         struct pid *pgrp;
 489         pid_t pgrp_nr;
 490         int retval = tty_check_change(real_tty);
 491
 492         if (retval == -EIO)
 493                 return -ENOTTY;
 494         if (retval)
 495                 return retval;
 496
 497         if (get_user(pgrp_nr, p))
 498                 return -EFAULT;
 499         if (pgrp_nr < 0)
 500                 return -EINVAL;
 501
 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))) {
 506                 retval = -ENOTTY;
 507                 goto out_unlock_ctrl;
 508         }
 509         rcu_read_lock();
 510         pgrp = find_vpid(pgrp_nr);
 511         retval = -ESRCH;
 512         if (!pgrp)
 513                 goto out_unlock;
 514         retval = -EPERM;
 515         if (session_of_pgrp(pgrp) != task_session(current))
 516                 goto out_unlock;
 517         retval = 0;
 518         put_pid(real_tty->pgrp);
 519         real_tty->pgrp = get_pid(pgrp);
 520 out_unlock:
 521         rcu_read_unlock();
 522 out_unlock_ctrl:
 523         spin_unlock_irq(&real_tty->ctrl_lock);
 524         return retval;
 525 }
 526
 527 /**
 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
 532  *
 533  *      Obtain the session id of the tty. If there is no session
 534  *      return an error.
 535  */
 536 static int tiocgsid(struct tty_struct *tty, struct tty_struct *real_tty, pid_t __user *p)
 537 {
 538         unsigned long flags;
 539         pid_t sid;
 540
 541         /*
 542          * (tty == real_tty) is a cheap way of
 543          * testing if the tty is NOT a master pty.
 544          */
 545         if (tty == real_tty && current->signal->tty != real_tty)
 546                 return -ENOTTY;
 547
 548         spin_lock_irqsave(&real_tty->ctrl_lock, flags);
 549         if (!real_tty->session)
 550                 goto err;
 551         sid = pid_vnr(real_tty->session);
 552         spin_unlock_irqrestore(&real_tty->ctrl_lock, flags);
 553
 554         return put_user(sid, p);
 555
 556 err:
 557         spin_unlock_irqrestore(&real_tty->ctrl_lock, flags);
 558         return -ENOTTY;
 559 }
 560
 561 /*
 562  * Called from tty_ioctl(). If tty is a pty then real_tty is the slave side,
 563  * if not then tty == real_tty.
 564  */
 565 long tty_jobctrl_ioctl(struct tty_struct *tty, struct tty_struct *real_tty,
 566                        struct file *file, unsigned int cmd, unsigned long arg)
 567 {
 568         void __user *p = (void __user *)arg;
 569
 570         switch (cmd) {
 571         case TIOCNOTTY:
 572                 if (current->signal->tty != tty)
 573                         return -ENOTTY;
 574                 no_tty();
 575                 return 0;
 576         case TIOCSCTTY:
 577                 return tiocsctty(real_tty, file, arg);
 578         case TIOCGPGRP:
 579                 return tiocgpgrp(tty, real_tty, p);
 580         case TIOCSPGRP:
 581                 return tiocspgrp(tty, real_tty, p);
 582         case TIOCGSID:
 583                 return tiocgsid(tty, real_tty, p);
 584         }
 585         return -ENOIOCTLCMD;
 586 }