Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965505AbdLRRQ4 (ORCPT ); Mon, 18 Dec 2017 12:16:56 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:38406 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S935277AbdLRQCH (ORCPT ); Mon, 18 Dec 2017 11:02:07 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Dmitry Vyukov , syzkaller@googlegroups.com, Jiri Slaby , Peter Hurley , One Thousand Gnomes , Sasha Levin Subject: [PATCH 4.9 097/177] tty: dont panic on OOM in tty_set_ldisc() Date: Mon, 18 Dec 2017 16:48:40 +0100 Message-Id: <20171218152914.978638279@linuxfoundation.org> X-Mailer: git-send-email 2.15.1 In-Reply-To: <20171218152909.823644066@linuxfoundation.org> References: <20171218152909.823644066@linuxfoundation.org> User-Agent: quilt/0.65 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5312 Lines: 181 4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Dmitry Vyukov [ Upstream commit 5362544bebe85071188dd9e479b5a5040841c895 ] 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: Dmitry Vyukov Cc: syzkaller@googlegroups.com Cc: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman Cc: Jiri Slaby Cc: Peter Hurley Cc: One Thousand Gnomes Signed-off-by: Greg Kroah-Hartman Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- drivers/tty/tty_ldisc.c | 85 +++++++++--------------------------------------- 1 file changed, 16 insertions(+), 69 deletions(-) --- a/drivers/tty/tty_ldisc.c +++ b/drivers/tty/tty_ldisc.c @@ -489,41 +489,6 @@ static void tty_ldisc_close(struct tty_s } /** - * 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 * @ldisc: the line discipline @@ -536,12 +501,7 @@ static void tty_ldisc_restore(struct tty 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 } /* 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 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 * 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); @@ -674,10 +623,8 @@ int tty_ldisc_reinit(struct tty_struct * 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; - } + tty_ldisc_put(tty->ldisc); + tty->ldisc = NULL; } return retval; }