// SPDX-License-Identifier: GPL-2.0
/*
* Copyright (C) 1991, 1992 Linus Torvalds
*/
#include <linux/types.h>
#include <linux/errno.h>
#include <linux/signal.h>
#include <linux/sched/signal.h>
#include <linux/sched/task.h>
#include <linux/tty.h>
#include <linux/fcntl.h>
#include <linux/uaccess.h>
#include "tty.h"
static int is_ignored(int sig)
{
return (sigismember(¤t->blocked, sig) ||
current->sighand->action[sig-1].sa.sa_handler == SIG_IGN);
}
/**
* __tty_check_change - check for POSIX terminal changes
* @tty: tty to check
* @sig: signal to send
*
* If we try to write to, or set the state of, a terminal and we're
* not in the foreground, send a SIGTTOU. If the signal is blocked or
* ignored, go ahead and perform the operation. (POSIX 7.2)
*
* Locking: ctrl.lock
*/
int __tty_check_change(struct tty_struct *tty, int sig)
{
unsigned long flags;
struct pid *pgrp, *tty_pgrp;
int ret = 0;
if (current->signal->tty != tty)
return 0;
rcu_read_lock();
pgrp = task_pgrp(current);
spin_lock_irqsave(&tty->ctrl.lock, flags);
tty_pgrp = tty->ctrl.pgrp;
spin_unlock_irqrestore(&tty->ctrl.lock, flags);
if (tty_pgrp && pgrp != tty_pgrp) {
if (is_ignored(sig)) {
if (sig == SIGTTIN)
ret = -EIO;
} else if (is_current_pgrp_orphaned())
ret = -EIO;
else {
kill_pgrp(pgrp, sig, 1);
set_thread_flag(TIF_SIGPENDING);
ret = -ERESTARTSYS;
}
}
rcu_read_unlock();
if (!tty_pgrp)
tty_warn(tty, "sig=%d, tty->pgrp == NULL!\n", sig);
return ret;
}
int tty_check_change(struct tty_struct *tty)
{
return __tty_check_change(tty, SIGTTOU);
}
EXPORT_SYMBOL(tty_check_change);
void proc_clear_tty(struct task_struct *p)
{
unsigned long flags;
struct tty_struct *tty;
spin_lock_irqsave(&p->sighand->siglock, flags);
tty = p->signal->tty;
p->signal->tty = NULL;
spin_unlock_irqrestore(&p->sighand->siglock, flags);
tty_kref_put(tty);
}
/**
* __proc_set_tty - set the controlling terminal
* @tty: tty structure
*
* Only callable by the session leader and only if it does not already have
* a controlling terminal.
*
* Caller must hold: tty_lock()
* a readlock on tasklist_lock
* sighand lock
*/
static void __proc_set_tty(struct tty_struct *tty)
{
unsigned long flags;
spin_lock_irqsave(&tty->ctrl.lock, flags);
/*
* The session and fg pgrp references will be non-NULL if
* tiocsctty() is stealing the controlling tty
*/
put_pid(tty->ctrl.session);
put_pid(tty->ctrl.pgrp);
tty->ctrl.pgrp = get_pid(task_pgrp(current));
tty->ctrl.session = get_pid(task_session(current));
spin_unlock_irqrestore(&tty->ctrl.lock, flags);
if (current->signal->tty) {
tty_debug(tty, "current tty %s not NULL!!\n",
current->signal->tty->name);
tty_kref_put(current->signal->tty);
}
put_pid(current->signal->tty_old_pgrp);
current->signal->tty = tty_kref_get(tty);
current->signal->tty_old_pgrp = NULL;
}
static void proc_set_tty(struct tty_struct *tty)
{
spin_lock_irq(¤t->sighand->siglock);
__proc_set_tty(tty);
spin_unlock_irq(¤t->sighand->siglock);
}
/*
* Called by tty_open() to set the controlling tty if applicable.
*/
void tty_open_proc_set_tty(struct file *filp, struct tty_struct *tty)
{
read_lock(&tasklist_lock);
spin_lock_irq(¤t->sighand->siglock);
if (current->signal->leader &&
!current->signal->tty &&
tty->ctrl.session == NULL) {
/*
* Don't let a process that only has write access to the tty
* obtain the privileges associated with having a tty as
* controlling terminal (being able to reopen it with full
* access through /dev/tty, being able to perform pushback).
* Many distributions set the group of all ttys to "tty" and
* grant write-only access to all terminals for setgid tty
* binaries, which should not imply full privileges on all ttys.
*
* This could theoretically break old code that performs open()
* on a write-only file descriptor. In that case, it might be
* necessary to also permit this if
* inode_permission(inode, MAY_READ) == 0.
*/
if (filp->f_mode & FMODE_READ)
__proc_set_tty(tty);
}
spin_unlock_irq(¤t->sighand->siglock);
read_unlock(&tasklist_lock);
}
struct tty_struct *get_current_tty(void)
{
struct tty_struct *tty;
unsigned long flags;
spin_lock_irqsave(¤t->sighand->siglock, flags);
tty = tty_kref_get(current->signal->tty);
spin_unlock_irqrestore(¤t->sighand->siglock, flags);
return tty;
}
EXPORT_SYMBOL_GPL(get_current_tty);
/*
* Called from tty_release().
*/
void session_clear_tty(struct pid *session)
{
struct task_struct *p;
do_each_pid_task(session, PIDTYPE_SID, p) {
proc_clear_tty(p);
} while_each_pid_task(session, PIDTYPE_SID, p);
}
/**
* tty_signal_session_leader - sends SIGHUP to session leader
* @tty: controlling tty
* @exit_session: if non-zero, signal all foreground group processes
*
* Send SIGHUP and SIGCONT to the session leader and its process group.
* Optionally, signal all processes in the foreground process group.
*
* Returns the number of processes in the session with this tty
* as their controlling terminal. This value is used to drop
* tty references for those processes.
*/
int tty_signal_session_leader(struct tty_struct *tty, int exit_session)
{
struct task_struct *p;
int refs = 0;
struct pid *tty_pgrp = NULL;
read_lock(&tasklist_lock);
if (tty->ctrl.session) {
do_each_pid_task(tty->ctrl.session, PIDTYPE_SID, p) {
spin_lock_irq(&p->sighand->siglock);
if (p->signal->tty == tty) {
p->signal->tty = NULL;
/*
* We defer the dereferences outside of
* the tasklist lock.
*/
refs++;
}
if (!p->signal->leader) {
spin_unlock_irq(&p->sighand->siglock);
continue;
}
send_signal_locked(SIGHUP, SEND_SIG_PRIV, p, PIDTYPE_TGID);
send_signal_locked(SIGCONT, SEND_SIG_PRIV, p, PIDTYPE_TGID);
put_pid(p->signal->tty_old_pgrp); /* A noop */
spin_lock(&tty->ctrl.lock);
tty_pgrp = get_pid(tty->ctrl.pgrp);
if (tty->ctrl.pgrp)
p->signal->tty_old_pgrp =
get_pid(tty->ctrl.pgrp);
spin_unlock(&tty->ctrl.lock);
spin_unlock_irq(&p->sighand->siglock);
} while_each_pid_task(tty->ctrl.session, PIDTYPE_SID, p);
}
read_unlock(&tasklist_lock);
if (tty_pgrp) {
if (exit_session)
kill_pgrp(tty_pgrp, SIGHUP, exit_session);
put_pid(tty_pgrp);
}
return refs;
}
/**
* disassociate_ctty - disconnect controlling tty
* @on_exit: true if exiting so need to "hang up" the session
*
* This function is typically called only by the session leader, when
* it wants to disassociate itself from its controlling tty.
*
* It performs the following functions:
* (1) Sends a SIGHUP and SIGCONT to the foreground process group
* (2) Clears the tty from being controlling the session
* (3) Clears the controlling tty for all processes in the
* session group.
*
* The argument on_exit is set to 1 if called when a process is
* exiting; it is 0 if called by the ioctl TIOCNOTTY.
*
* Locking:
* BTM is taken for hysterical raisons, and held when
* called from no_tty().
* tty_mutex is taken to protect tty
* ->siglock is taken to protect ->signal/->sighand
* tasklist_lock is taken to walk process list for sessions
* ->siglock is taken to protect ->signal/->sighand
*/
void disassociate_ctty(int on_exit)
{
struct tty_struct *tty;
if (!current->signal->leader)
return;
tty = get_current_tty();
if (tty) {
if (on_exit && tty->driver->type != TTY_DRIVER_TYPE_PTY) {
tty_vhangup_session(tty);
} else {
struct pid *tty_pgrp = tty_get_pgrp(tty);
if (tty_pgrp) {
kill_pgrp(tty_pgrp, SIGHUP, on_exit);
if (!on_exit)
kill_pgrp(tty_pgrp, SIGCONT, on_exit);
put_pid(tty_pgrp);
}
}
tty_kref_put(tty);
} else if (on_exit) {
struct pid *old_pgrp;
spin_lock_irq(¤t->sighand->siglock);
old_pgrp = current->signal->tty_old_pgrp;
current->signal->tty_old_pgrp = NULL;
spin_unlock_irq(¤t->sighand->siglock);
if (old_pgrp) {
kill_pgrp(old_pgrp, SIGHUP, on_exit);
kill_pgrp(old_pgrp, SIGCONT, on_exit);
put_pid(old_pgrp);
}
return;
}
tty = get_current_tty();
if (tty) {
unsigned long flags;
tty_lock(tty);
spin_lock_irqsave(&tty->ctrl.lock, flags);
put_pid(tty->ctrl.session);
put_pid(tty->ctrl.pgrp);
tty->ctrl.session = NULL;
tty->ctrl.pgrp = NULL;
spin_unlock_irqrestore(&tty->ctrl.lock, flags);
tty_unlock(tty);
tty_kref_put(tty);
}
/* If tty->ctrl.pgrp is not NULL, it may be assigned to
* current->signal->tty_old_pgrp in a race condition, and
* cause pid memleak. Release current->signal->tty_old_pgrp
* after tty->ctrl.pgrp set to NULL.
*/
spin_lock_irq(¤t->sighand->siglock);
put_pid(current->signal->tty_old_pgrp);
current->signal->tty_old_pgrp = NULL;
spin_unlock_irq(¤t->sighand->siglock);
/* Now clear signal->tty under the lock */
read_lock(&tasklist_lock);
session_clear_tty(task_session(current));
read_unlock(&tasklist_lock);
}
/*
*
* no_tty - Ensure the current process does not have a controlling tty
*/
void no_tty(void)
{
/*
* FIXME: Review locking here. The tty_lock never covered any race
* between a new association and proc_clear_tty but possibly we need
* to protect against this anyway.
*/
struct task_struct *tsk = current;
disassociate_ctty(0);
proc_clear_tty(tsk);
}
/**
* tiocsctty - set controlling tty
* @tty: tty structure
* @file: file structure used to check permissions
* @arg: user argument
*
* This ioctl is used to manage job control. It permits a session
* leader to set this tty as the controlling tty for the session.
*
* Locking:
* Takes tty_lock() to serialize proc_set_tty() for this tty
* Takes tasklist_lock internally to walk sessions
* Takes ->siglock() when updating signal->tty
*/
static int tiocsctty(struct tty_struct *tty, struct file *file, int arg)
{
int ret = 0;
tty_lock(tty);
read_lock(&tasklist_lock);
if (current->signal->leader &&
task_session(current) == tty->ctrl.session)
goto unlock;
/*
* The process must be a session leader and
* not have a controlling tty already.
*/
if (!current->signal->leader || current->signal->tty) {
ret = -EPERM;
goto unlock;
}
if (tty->ctrl.session) {
/*
* This tty is already the controlling
* tty for another session group!
*/
if (arg == 1 && capable(CAP_SYS_ADMIN)) {
/*
* Steal it away
*/
session_clear_tty(tty->ctrl.session);
} else {
ret = -EPERM;
goto unlock;
}
}
/* See the comment in tty_open_proc_set_tty(). */
if ((file->f_mode & FMODE_READ) == 0 && !capable(CAP_SYS_ADMIN)) {
ret = -EPERM;
goto unlock;
}
proc_set_tty(tty);
unlock:
read_unlock(&tasklist_lock);
tty_unlock(tty);
return ret;
}
/**
* tty_get_pgrp - return a ref counted pgrp pid
* @tty: tty to read
*
* Returns a refcounted instance of the pid struct for the process
* group controlling the tty.
*/
struct pid *tty_get_pgrp(struct tty_struct *tty)
{
unsigned long flags;
struct pid *pgrp;
spin_lock_irqsave(&tty->ctrl.lock, flags);
pgrp = get_pid(tty->ctrl.pgrp);
spin_unlock_irqrestore(&tty->ctrl.lock, flags);
return pgrp;
}
EXPORT_SYMBOL_GPL(tty_get_pgrp);
/*
* This checks not only the pgrp, but falls back on the pid if no
* satisfactory pgrp is found. I dunno - gdb doesn't work correctly
* without this...
*
* The caller must hold rcu lock or the tasklist lock.
*/
static struct pid *session_of_pgrp(struct pid *pgrp)
{
struct task_struct *p;
struct pid *sid = NULL;
p = pid_task(pgrp, PIDTYPE_PGID);
if (p == NULL)
p = pid_task(pgrp, PIDTYPE_PID);
if (p != NULL)
sid = task_session(p);
return sid;
}
/**
* tiocgpgrp - get process group
* @tty: tty passed by user
* @real_tty: tty side of the tty passed by the user if a pty else the tty
* @p: returned pid
*
* Obtain the process group of the tty. If there is no process group
* return an error.
*
* Locking: none. Reference to current->signal->tty is safe.
*/
static int tiocgpgrp(struct tty_struct *tty, struct tty_struct *real_tty, pid_t __user *p)
{
struct pid *pid;
int ret;
/*
* (tty == real_tty) is a cheap way of
* testing if the tty is NOT a master pty.
*/
if (tty == real_tty && current->signal->tty != real_tty)
return -ENOTTY;
pid = tty_get_pgrp(real_tty);
ret = put_user(pid_vnr(pid), p);
put_pid(pid);
return ret;
}
/**
* tiocspgrp - attempt to set process group
* @tty: tty passed by user
* @real_tty: tty side device matching tty passed by user
* @p: pid pointer
*
* Set the process group of the tty to the session passed. Only
* permitted where the tty session is our session.
*
* Locking: RCU, ctrl lock
*/
static int tiocspgrp(struct tty_struct *tty, struct tty_struct *real_tty, pid_t __user *p)
{
struct pid *pgrp;
pid_t pgrp_nr;
int retval = tty_check_change(real_tty);
if (retval == -EIO)
return -ENOTTY;
if (retval)
return retval;
if (get_user(pgrp_nr, p))
return -EFAULT;
if (pgrp_nr < 0)
return -EINVAL;
spin_lock_irq(&real_tty->ctrl.lock);
if (!current->signal->tty ||
(current->signal->tty != real_tty) ||
(real_tty->ctrl.session != task_session(current))) {
retval = -ENOTTY;
goto out_unlock_ctrl;
}
rcu_read_lock();
pgrp = find_vpid(pgrp_nr);
retval = -ESRCH;
if (!pgrp)
goto out_unlock;
retval = -EPERM;
if (session_of_pgrp(pgrp) != task_session(current))
goto out_unlock;
retval = 0;
put_pid(real_tty->ctrl.pgrp);
real_tty->ctrl.pgrp = get_pid(pgrp);
out_unlock:
rcu_read_unlock();
out_unlock_ctrl:
spin_unlock_irq(&real_tty->ctrl.lock);
return retval;
}
/**
* tiocgsid - get session id
* @tty: tty passed by user
* @real_tty: tty side of the tty passed by the user if a pty else the tty
* @p: pointer to returned session id
*
* Obtain the session id of the tty. If there is no session
* return an error.
*/
static int tiocgsid(struct tty_struct *tty, struct tty_struct *real_tty, pid_t __user *p)
{
unsigned long flags;
pid_t sid;
/*
* (tty == real_tty) is a cheap way of
* testing if the tty is NOT a master pty.
*/
if (tty == real_tty && current->signal->tty != real_tty)
return -ENOTTY;
spin_lock_irqsave(&real_tty->ctrl.lock, flags);
if (!real_tty->ctrl.session)
goto err;
sid = pid_vnr(real_tty->ctrl.session);
spin_unlock_irqrestore(&real_tty->ctrl.lock, flags);
return put_user(sid, p);
err:
spin_unlock_irqrestore(&real_tty->ctrl.lock, flags);
return -ENOTTY;
}
/*
* Called from tty_ioctl(). If tty is a pty then real_tty is the slave side,
* if not then tty == real_tty.
*/
long tty_jobctrl_ioctl(struct tty_struct *tty, struct tty_struct *real_tty,
struct file *file, unsigned int cmd, unsigned long arg)
{
void __user *p = (void __user *)arg;
switch (cmd) {
case TIOCNOTTY:
if (current->signal->tty != tty)
return -ENOTTY;
no_tty();
return 0;
case TIOCSCTTY:
return tiocsctty(real_tty, file, arg);
case TIOCGPGRP:
return tiocgpgrp(tty, real_tty, p);
case TIOCSPGRP:
return tiocspgrp(tty, real_tty, p);
case TIOCGSID:
return tiocgsid(tty, real_tty, p);
}
return -ENOIOCTLCMD;
}
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