linux/drivers/tty/tty_jobctrl.c
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   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
  16static 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 */
  33int __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
  69int tty_check_change(struct tty_struct *tty)
  70{
  71        return __tty_check_change(tty, SIGTTOU);
  72}
  73EXPORT_SYMBOL(tty_check_change);
  74
  75void 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 */
  98static 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
 122static 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 */
 132void 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
 160struct 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}
 170EXPORT_SYMBOL_GPL(get_current_tty);
 171
 172/*
 173 * Called from tty_release().
 174 */
 175void 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 */
 196int 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 */
 264void 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 */
 332void 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 */
 359static 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);
 401unlock:
 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 */
 414struct 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}
 425EXPORT_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 */
 434static 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 */
 459static 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 */
 486static 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);
 520out_unlock:
 521        rcu_read_unlock();
 522out_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 */
 536static 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
 556err:
 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 */
 565long 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}
 587