From: Dmitry Vyukov dvyukov@google.com
[ 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 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: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Sasha Levin alexander.levin@verizon.com --- drivers/tty/tty_ldisc.c | 85 ++++++++++--------------------------------------- 1 file changed, 16 insertions(+), 69 deletions(-)
diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c index 68947f6de5ad..c3956ca022e4 100644 --- a/drivers/tty/tty_ldisc.c +++ b/drivers/tty/tty_ldisc.c @@ -489,41 +489,6 @@ static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *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 * @ldisc: the line discipline @@ -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); @@ -674,10 +623,8 @@ 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; - } + tty_ldisc_put(tty->ldisc); + tty->ldisc = NULL; } return retval; }