tty: split job control support into a file of its own

This makes it easier for job control to become optional and/or usable
independently from tty_io.c, as well as providing a nice purpose
separation. No logical changes from this patch.

Signed-off-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/Makefile

@@ -1,6 +1,6 @@
 obj-$(CONFIG_TTY)		+= tty_io.o n_tty.o tty_ioctl.o tty_ldisc.o \
 				   tty_buffer.o tty_port.o tty_mutex.o \
-				   tty_ldsem.o tty_baudrate.o
+				   tty_ldsem.o tty_baudrate.o tty_jobctrl.o
 obj-$(CONFIG_LEGACY_PTYS)	+= pty.o
 obj-$(CONFIG_UNIX98_PTYS)	+= pty.o
 obj-$(CONFIG_AUDIT)		+= tty_audit.o

drivers/tty/tty_io.c

@@ -377,65 +377,6 @@ struct tty_driver *tty_find_polling_driver(char *name, int *line)
 EXPORT_SYMBOL_GPL(tty_find_polling_driver);
 #endif
 
-static int is_ignored(int sig)
-{
-	return (sigismember(&current->blocked, sig) ||
-		current->sighand->action[sig-1].sa.sa_handler == SIG_IGN);
-}
-
-/**
- *	tty_check_change	-	check for POSIX terminal changes
- *	@tty: tty to check
- *
- *	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->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);
-
 static ssize_t hung_up_tty_read(struct file *file, char __user *buf,
 				size_t count, loff_t *ppos)
 {
@@ -509,79 +450,6 @@ static const struct file_operations hung_up_tty_fops = {
 static DEFINE_SPINLOCK(redirect_lock);
 static struct file *redirect;
 
-
-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
- *
- * 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->session);
-	put_pid(tty->pgrp);
-	tty->pgrp = get_pid(task_pgrp(current));
-	spin_unlock_irqrestore(&tty->ctrl_lock, flags);
-	tty->session = get_pid(task_session(current));
-	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(&current->sighand->siglock);
-	__proc_set_tty(tty);
-	spin_unlock_irq(&current->sighand->siglock);
-}
-
-struct tty_struct *get_current_tty(void)
-{
-	struct tty_struct *tty;
-	unsigned long flags;
-
-	spin_lock_irqsave(&current->sighand->siglock, flags);
-	tty = tty_kref_get(current->signal->tty);
-	spin_unlock_irqrestore(&current->sighand->siglock, flags);
-	return tty;
-}
-EXPORT_SYMBOL_GPL(get_current_tty);
-
-static 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_wakeup	-	request more data
  *	@tty: terminal
@@ -608,60 +476,6 @@ void tty_wakeup(struct tty_struct *tty)
 
 EXPORT_SYMBOL_GPL(tty_wakeup);
 
-/**
- *	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.
- */
-static 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->session) {
-		do_each_pid_task(tty->session, PIDTYPE_SID, p) {
-			spin_lock_irq(&p->sighand->siglock);
-			if (p->signal->tty == tty) {
-				p->signal->tty = NULL;
-				/* We defer the dereferences outside fo
-				   the tasklist lock */
-				refs++;
-			}
-			if (!p->signal->leader) {
-				spin_unlock_irq(&p->sighand->siglock);
-				continue;
-			}
-			__group_send_sig_info(SIGHUP, SEND_SIG_PRIV, p);
-			__group_send_sig_info(SIGCONT, SEND_SIG_PRIV, p);
-			put_pid(p->signal->tty_old_pgrp);  /* A noop */
-			spin_lock(&tty->ctrl_lock);
-			tty_pgrp = get_pid(tty->pgrp);
-			if (tty->pgrp)
-				p->signal->tty_old_pgrp = get_pid(tty->pgrp);
-			spin_unlock(&tty->ctrl_lock);
-			spin_unlock_irq(&p->sighand->siglock);
-		} while_each_pid_task(tty->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;
-}
-
 /**
  *	__tty_hangup		-	actual handler for hangup events
  *	@work: tty device
@@ -840,7 +654,7 @@ void tty_vhangup_self(void)
  *	is complete. That guarantee is necessary for security reasons.
  */
 
-static void tty_vhangup_session(struct tty_struct *tty)
+void tty_vhangup_session(struct tty_struct *tty)
 {
 	tty_debug_hangup(tty, "session hangup\n");
 	__tty_hangup(tty, 1);
@@ -861,106 +675,6 @@ int tty_hung_up_p(struct file *filp)
 
 EXPORT_SYMBOL(tty_hung_up_p);
 
-/**
- *	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 raisins, 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(&current->sighand->siglock);
-		old_pgrp = current->signal->tty_old_pgrp;
-		current->signal->tty_old_pgrp = NULL;
-		spin_unlock_irq(&current->sighand->siglock);
-		if (old_pgrp) {
-			kill_pgrp(old_pgrp, SIGHUP, on_exit);
-			kill_pgrp(old_pgrp, SIGCONT, on_exit);
-			put_pid(old_pgrp);
-		}
-		return;
-	}
-
-	spin_lock_irq(&current->sighand->siglock);
-	put_pid(current->signal->tty_old_pgrp);
-	current->signal->tty_old_pgrp = NULL;
-
-	tty = tty_kref_get(current->signal->tty);
-	if (tty) {
-		unsigned long flags;
-		spin_lock_irqsave(&tty->ctrl_lock, flags);
-		put_pid(tty->session);
-		put_pid(tty->pgrp);
-		tty->session = NULL;
-		tty->pgrp = NULL;
-		spin_unlock_irqrestore(&tty->ctrl_lock, flags);
-		tty_kref_put(tty);
-	} else
-		tty_debug_hangup(tty, "no current tty\n");
-
-	spin_unlock_irq(&current->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 possible we need
-	   to protect against this anyway */
-	struct task_struct *tsk = current;
-	disassociate_ctty(0);
-	proc_clear_tty(tsk);
-}
-
-
 /**
  *	stop_tty	-	propagate flow control
  *	@tty: tty to stop
@@ -2163,38 +1877,13 @@ retry_open:
 	}
 	clear_bit(TTY_HUPPED, &tty->flags);
 
-
-	read_lock(&tasklist_lock);
-	spin_lock_irq(&current->sighand->siglock);
 	noctty = (filp->f_flags & O_NOCTTY) ||
-			(IS_ENABLED(CONFIG_VT) && device == MKDEV(TTY_MAJOR, 0)) ||
-			device == MKDEV(TTYAUX_MAJOR, 1) ||
-			(tty->driver->type == TTY_DRIVER_TYPE_PTY &&
-			 tty->driver->subtype == PTY_TYPE_MASTER);
-
-	if (!noctty &&
-	    current->signal->leader &&
-	    !current->signal->tty &&
-	    tty->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(&current->sighand->siglock);
-	read_unlock(&tasklist_lock);
+		 (IS_ENABLED(CONFIG_VT) && device == MKDEV(TTY_MAJOR, 0)) ||
+		 device == MKDEV(TTYAUX_MAJOR, 1) ||
+		 (tty->driver->type == TTY_DRIVER_TYPE_PTY &&
+		  tty->driver->subtype == PTY_TYPE_MASTER);
+	if (!noctty)
+		tty_open_proc_set_tty(filp, tty);
 	tty_unlock(tty);
 	return 0;
 }
@@ -2456,211 +2145,6 @@ static int fionbio(struct file *file, int __user *p)
 	return 0;
 }
 
-/**
- *	tiocsctty	-	set controlling tty
- *	@tty: tty structure
- *	@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->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->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->session);
-		} else {
-			ret = -EPERM;
-			goto unlock;
-		}
-	}
-
-	/* See the comment in tty_open(). */
-	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->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 (!current->signal->tty ||
-	    (current->signal->tty != real_tty) ||
-	    (real_tty->session != task_session(current)))
-		return -ENOTTY;
-	if (get_user(pgrp_nr, p))
-		return -EFAULT;
-	if (pgrp_nr < 0)
-		return -EINVAL;
-	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;
-	spin_lock_irq(&tty->ctrl_lock);
-	put_pid(real_tty->pgrp);
-	real_tty->pgrp = get_pid(pgrp);
-	spin_unlock_irq(&tty->ctrl_lock);
-out_unlock:
-	rcu_read_unlock();
-	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.
- *
- *	Locking: none. Reference to current->signal->tty is safe.
- */
-
-static int tiocgsid(struct tty_struct *tty, struct tty_struct *real_tty, pid_t __user *p)
-{
-	/*
-	 * (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;
-	if (!real_tty->session)
-		return -ENOTTY;
-	return put_user(pid_vnr(real_tty->session), p);
-}
-
 /**
  *	tiocsetd	-	set line discipline
  *	@tty: tty device
@@ -2920,19 +2404,6 @@ long tty_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 		int excl = test_bit(TTY_EXCLUSIVE, &tty->flags);
 		return put_user(excl, (int __user *)p);
 	}
-	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);
 	case TIOCGETD:
 		return tiocgetd(tty, p);
 	case TIOCSETD:
@@ -2993,6 +2464,10 @@ long tty_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 	case TIOCSSERIAL:
 		tty_warn_deprecated_flags(p);
 		break;
+	default:
+		retval = tty_jobctrl_ioctl(tty, real_tty, file, cmd, arg);
+		if (retval != -ENOIOCTLCMD)
+			return retval;
 	}
 	if (tty->ops->ioctl) {
 		retval = tty->ops->ioctl(tty, cmd, arg);

drivers/tty/tty_jobctrl.c

@@ -0,0 +1,554 @@
+/*
+ *  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>
+
+static int is_ignored(int sig)
+{
+	return (sigismember(&current->blocked, sig) ||
+		current->sighand->action[sig-1].sa.sa_handler == SIG_IGN);
+}
+
+/**
+ *	tty_check_change	-	check for POSIX terminal changes
+ *	@tty: tty to check
+ *
+ *	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->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
+ *
+ * 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->session);
+	put_pid(tty->pgrp);
+	tty->pgrp = get_pid(task_pgrp(current));
+	spin_unlock_irqrestore(&tty->ctrl_lock, flags);
+	tty->session = get_pid(task_session(current));
+	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(&current->sighand->siglock);
+	__proc_set_tty(tty);
+	spin_unlock_irq(&current->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(&current->sighand->siglock);
+	if (current->signal->leader &&
+	    !current->signal->tty &&
+	    tty->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(&current->sighand->siglock);
+	read_unlock(&tasklist_lock);
+}
+
+struct tty_struct *get_current_tty(void)
+{
+	struct tty_struct *tty;
+	unsigned long flags;
+
+	spin_lock_irqsave(&current->sighand->siglock, flags);
+	tty = tty_kref_get(current->signal->tty);
+	spin_unlock_irqrestore(&current->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->session) {
+		do_each_pid_task(tty->session, PIDTYPE_SID, p) {
+			spin_lock_irq(&p->sighand->siglock);
+			if (p->signal->tty == tty) {
+				p->signal->tty = NULL;
+				/* We defer the dereferences outside fo
+				   the tasklist lock */
+				refs++;
+			}
+			if (!p->signal->leader) {
+				spin_unlock_irq(&p->sighand->siglock);
+				continue;
+			}
+			__group_send_sig_info(SIGHUP, SEND_SIG_PRIV, p);
+			__group_send_sig_info(SIGCONT, SEND_SIG_PRIV, p);
+			put_pid(p->signal->tty_old_pgrp);  /* A noop */
+			spin_lock(&tty->ctrl_lock);
+			tty_pgrp = get_pid(tty->pgrp);
+			if (tty->pgrp)
+				p->signal->tty_old_pgrp = get_pid(tty->pgrp);
+			spin_unlock(&tty->ctrl_lock);
+			spin_unlock_irq(&p->sighand->siglock);
+		} while_each_pid_task(tty->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(&current->sighand->siglock);
+		old_pgrp = current->signal->tty_old_pgrp;
+		current->signal->tty_old_pgrp = NULL;
+		spin_unlock_irq(&current->sighand->siglock);
+		if (old_pgrp) {
+			kill_pgrp(old_pgrp, SIGHUP, on_exit);
+			kill_pgrp(old_pgrp, SIGCONT, on_exit);
+			put_pid(old_pgrp);
+		}
+		return;
+	}
+
+	spin_lock_irq(&current->sighand->siglock);
+	put_pid(current->signal->tty_old_pgrp);
+	current->signal->tty_old_pgrp = NULL;
+
+	tty = tty_kref_get(current->signal->tty);
+	if (tty) {
+		unsigned long flags;
+		spin_lock_irqsave(&tty->ctrl_lock, flags);
+		put_pid(tty->session);
+		put_pid(tty->pgrp);
+		tty->session = NULL;
+		tty->pgrp = NULL;
+		spin_unlock_irqrestore(&tty->ctrl_lock, flags);
+		tty_kref_put(tty);
+	}
+
+	spin_unlock_irq(&current->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 possible 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
+ *	@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->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->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->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->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 (!current->signal->tty ||
+	    (current->signal->tty != real_tty) ||
+	    (real_tty->session != task_session(current)))
+		return -ENOTTY;
+	if (get_user(pgrp_nr, p))
+		return -EFAULT;
+	if (pgrp_nr < 0)
+		return -EINVAL;
+	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;
+	spin_lock_irq(&tty->ctrl_lock);
+	put_pid(real_tty->pgrp);
+	real_tty->pgrp = get_pid(pgrp);
+	spin_unlock_irq(&tty->ctrl_lock);
+out_unlock:
+	rcu_read_unlock();
+	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.
+ *
+ *	Locking: none. Reference to current->signal->tty is safe.
+ */
+static int tiocgsid(struct tty_struct *tty, struct tty_struct *real_tty, pid_t __user *p)
+{
+	/*
+	 * (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;
+	if (!real_tty->session)
+		return -ENOTTY;
+	return put_user(pid_vnr(real_tty->session), p);
+}
+
+/*
+ * 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;
+}

include/linux/tty.h

@@ -475,9 +475,13 @@ extern int tty_do_resize(struct tty_struct *tty, struct winsize *ws);
 extern int is_current_pgrp_orphaned(void);
 extern void tty_hangup(struct tty_struct *tty);
 extern void tty_vhangup(struct tty_struct *tty);
+extern void tty_vhangup_session(struct tty_struct *tty);
 extern int tty_hung_up_p(struct file *filp);
 extern void do_SAK(struct tty_struct *tty);
 extern void __do_SAK(struct tty_struct *tty);
+extern void tty_open_proc_set_tty(struct file *filp, struct tty_struct *tty);
+extern int tty_signal_session_leader(struct tty_struct *tty, int exit_session);
+extern void session_clear_tty(struct pid *session);
 extern void no_tty(void);
 extern void tty_buffer_free_all(struct tty_port *port);
 extern void tty_buffer_flush(struct tty_struct *tty, struct tty_ldisc *ld);
@@ -525,6 +529,8 @@ extern void tty_ldisc_flush(struct tty_struct *tty);
 extern long tty_ioctl(struct file *file, unsigned int cmd, unsigned long arg);
 extern int tty_mode_ioctl(struct tty_struct *tty, struct file *file,
 			unsigned int cmd, unsigned long arg);
+extern long tty_jobctrl_ioctl(struct tty_struct *tty, struct tty_struct *real_tty,
+			      struct file *file, unsigned int cmd, unsigned long arg);
 extern int tty_perform_flush(struct tty_struct *tty, unsigned long arg);
 extern void tty_default_fops(struct file_operations *fops);
 extern struct tty_struct *alloc_tty_struct(struct tty_driver *driver, int idx);