Commit 5362544b authored by Dmitry Vyukov's avatar Dmitry Vyukov Committed by Greg Kroah-Hartman
Browse files

tty: don't panic on OOM in tty_set_ldisc() 



If tty_ldisc_open() fails in tty_set_ldisc(), it tries to go back
to the old discipline or N_TTY. But that can fail as well, in such
case it panics. This is not a graceful way to handle OOM.

Leave ldisc==NULL if all attempts fail instead.
Also use existing tty_ldisc_reinit() helper function instead of
tty_ldisc_restore(). Also don't WARN/BUG in tty_ldisc_reinit()
if N_TTY fails, which would have the same net effect of bringing
kernel down on OOM. Instead print a single line message about
what has happened.

Signed-off-by: default avatarDmitry Vyukov <dvyukov@google.com>
Cc: syzkaller@googlegroups.com
Cc: linux-kernel@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jslaby@suse.com>
Cc: Peter Hurley <peter@hurleysoftware.com>
Cc: One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent b767ad72

drivers/tty/tty_ldisc.c

+16 −69
Original line number Diff line number Diff line
@@ -488,41 +488,6 @@ static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *ld) 
	tty_ldisc_debug(tty, "%p: closed\n", ld);

}



/**

 *	tty_ldisc_restore	-	helper for tty ldisc change

 *	@tty: tty to recover

 *	@old: previous ldisc

 *

 *	Restore the previous line discipline or N_TTY when a line discipline

 *	change fails due to an open error

 */



static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old)

{

	struct tty_ldisc *new_ldisc;

	int r;



	/* There is an outstanding reference here so this is safe */

	old = tty_ldisc_get(tty, old->ops->num);

	WARN_ON(IS_ERR(old));

	tty->ldisc = old;

	tty_set_termios_ldisc(tty, old->ops->num);

	if (tty_ldisc_open(tty, old) < 0) {

		tty_ldisc_put(old);

		/* This driver is always present */

		new_ldisc = tty_ldisc_get(tty, N_TTY);

		if (IS_ERR(new_ldisc))

			panic("n_tty: get");

		tty->ldisc = new_ldisc;

		tty_set_termios_ldisc(tty, N_TTY);

		r = tty_ldisc_open(tty, new_ldisc);

		if (r < 0)

			panic("Couldn't open N_TTY ldisc for "

			      "%s --- error %d.",

			      tty_name(tty), r);

	}

}



/**

 *	tty_set_ldisc		-	set line discipline

 *	@tty: the terminal to set
@@ -536,12 +501,7 @@ static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old) 


int tty_set_ldisc(struct tty_struct *tty, int disc)

{

	int retval;

	struct tty_ldisc *old_ldisc, *new_ldisc;



	new_ldisc = tty_ldisc_get(tty, disc);

	if (IS_ERR(new_ldisc))

		return PTR_ERR(new_ldisc);

	int retval, old_disc;



	tty_lock(tty);

	retval = tty_ldisc_lock(tty, 5 * HZ);
@@ -554,7 +514,8 @@ int tty_set_ldisc(struct tty_struct *tty, int disc) 
	}



	/* Check the no-op case */

	if (tty->ldisc->ops->num == disc)

	old_disc = tty->ldisc->ops->num;

	if (old_disc == disc)

		goto out;



	if (test_bit(TTY_HUPPED, &tty->flags)) {
@@ -563,34 +524,25 @@ int tty_set_ldisc(struct tty_struct *tty, int disc) 
		goto out;

	}



	old_ldisc = tty->ldisc;



	/* Shutdown the old discipline. */

	tty_ldisc_close(tty, old_ldisc);



	/* Now set up the new line discipline. */

	tty->ldisc = new_ldisc;

	tty_set_termios_ldisc(tty, disc);



	retval = tty_ldisc_open(tty, new_ldisc);

	retval = tty_ldisc_reinit(tty, disc);

	if (retval < 0) {

		/* Back to the old one or N_TTY if we can't */

		tty_ldisc_put(new_ldisc);

		tty_ldisc_restore(tty, old_ldisc);

		if (tty_ldisc_reinit(tty, old_disc) < 0) {

			pr_err("tty: TIOCSETD failed, reinitializing N_TTY\n");

			if (tty_ldisc_reinit(tty, N_TTY) < 0) {

				/* At this point we have tty->ldisc == NULL. */

				pr_err("tty: reinitializing N_TTY failed\n");

			}

		}

	}



	if (tty->ldisc->ops->num != old_ldisc->ops->num && tty->ops->set_ldisc) {

	if (tty->ldisc && tty->ldisc->ops->num != old_disc &&

	    tty->ops->set_ldisc) {

		down_read(&tty->termios_rwsem);

		tty->ops->set_ldisc(tty);

		up_read(&tty->termios_rwsem);

	}



	/* At this point we hold a reference to the new ldisc and a

	   reference to the old ldisc, or we hold two references to

	   the old ldisc (if it was restored as part of error cleanup

	   above). In either case, releasing a single reference from

	   the old ldisc is correct. */

	new_ldisc = old_ldisc;

out:

	tty_ldisc_unlock(tty);
@@ -598,7 +550,6 @@ out: 
	   already running */

	tty_buffer_restart_work(tty->port);

err:

	tty_ldisc_put(new_ldisc);	/* drop the extra reference */

	tty_unlock(tty);

	return retval;

}
@@ -659,10 +610,8 @@ int tty_ldisc_reinit(struct tty_struct *tty, int disc) 
	int retval;



	ld = tty_ldisc_get(tty, disc);

	if (IS_ERR(ld)) {

		BUG_ON(disc == N_TTY);

	if (IS_ERR(ld))

		return PTR_ERR(ld);

	}



	if (tty->ldisc) {

		tty_ldisc_close(tty, tty->ldisc);
@@ -674,11 +623,9 @@ int tty_ldisc_reinit(struct tty_struct *tty, int disc) 
	tty_set_termios_ldisc(tty, disc);

	retval = tty_ldisc_open(tty, tty->ldisc);

	if (retval) {

		if (!WARN_ON(disc == N_TTY)) {

		tty_ldisc_put(tty->ldisc);

		tty->ldisc = NULL;

	}

	}

	return retval;

}

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