diff options
author | Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> | 2018-04-16 14:06:34 +0300 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2018-05-01 22:58:13 +0300 |
commit | 877f418171af2aae702cf0878ae2ec44eab5e89a (patch) | |
tree | cb3b9ee9e1785b67f6ad0ef86e4f4935ce0bae44 /drivers | |
parent | 6a50af86a62be245cf093c3de2c02790da1491df (diff) | |
download | linux-877f418171af2aae702cf0878ae2ec44eab5e89a.tar.xz |
tty: Avoid possible error pointer dereference at tty_ldisc_restore().
commit 598c2d41ff44889dd8eced4f117403e472158d85 upstream.
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@syzkaller.appspotmail.com
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jslaby@suse.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Alan Cox <alan@llwyncelyn.cymru>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Michal Hocko <mhocko@suse.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers')
-rw-r--r-- | drivers/tty/tty_ldisc.c | 13 |
1 files changed, 5 insertions, 8 deletions
diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c index 77eac4ab1737..b36f4aa05b92 100644 --- a/drivers/tty/tty_ldisc.c +++ b/drivers/tty/tty_ldisc.c @@ -526,19 +526,16 @@ 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); } } |