This is a note to let you know that I've just added the patch titled
tty: Avoid possible error pointer dereference at tty_ldisc_restore().
to my tty git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git
in the tty-linus branch.
The patch will show up in the next release of the linux-next tree
(usually sometime within the next 24 hours during the week.)
The patch will hopefully also be merged in Linus's tree for the
next -rc kernel release.
If you have any questions about this process, please let me know.
>From 598c2d41ff44889dd8eced4f117403e472158d85 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Date: Mon, 16 Apr 2018 20:06:34 +0900
Subject: tty: Avoid possible error pointer dereference at tty_ldisc_restore().
syzbot is reporting crashes [1] triggered by memory allocation failure at
tty_ldisc_get() from tty_ldisc_restore(). While syzbot stops at WARN_ON()
due to panic_on_warn == true, panic_on_warn == false will after all trigger
an OOPS by dereferencing old->ops->num if IS_ERR(old) == true.
We can simplify tty_ldisc_restore() as three calls (old->ops->num, N_TTY,
N_NULL) to tty_ldisc_failto() in addition to avoiding possible error
pointer dereference.
If someone reports kernel panic triggered by forcing all memory allocations
for tty_ldisc_restore() to fail, we can consider adding __GFP_NOFAIL for
tty_ldisc_restore() case.
[1] https://syzkaller.appspot.com/bug?id=6ac359c61e71d22e06db7f8f88243feb11d927e7
Reported-by: syzbot+40b7287c2dc987c48c81@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Jiri Slaby <jslaby@xxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Alan Cox <alan@llwyncelyn.cymru>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: stable <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/tty/tty_ldisc.c | 13 +++++--------
1 file changed, 5 insertions(+), 8 deletions(-)
diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
index 050f4d650891..c1cf6cb83185 100644
--- a/drivers/tty/tty_ldisc.c
+++ b/drivers/tty/tty_ldisc.c
@@ -527,19 +527,16 @@ static int tty_ldisc_failto(struct tty_struct *tty, int ld)
static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old)
{
/* 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);
+ if (tty_ldisc_failto(tty, old->ops->num) < 0) {
+ const char *name = tty_name(tty);
+
+ pr_warn("Falling back ldisc for %s.\n", name);
/* The traditional behaviour is to fall back to N_TTY, we
want to avoid falling back to N_NULL unless we have no
choice to avoid the risk of breaking anything */
if (tty_ldisc_failto(tty, N_TTY) < 0 &&
tty_ldisc_failto(tty, N_NULL) < 0)
- panic("Couldn't open N_NULL ldisc for %s.",
- tty_name(tty));
+ panic("Couldn't open N_NULL ldisc for %s.", name);
}
}
--
2.17.0