3.16.60-rc1 review patch. If anyone has any objections, please let me know.
------------------ From: Tetsuo Handa <penguin-ker...@i-love.sakura.ne.jp> 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+40b7287c2dc987c48...@syzkaller.appspotmail.com Signed-off-by: Tetsuo Handa <penguin-ker...@i-love.sakura.ne.jp> Cc: Greg Kroah-Hartman <gre...@linuxfoundation.org> Cc: Jiri Slaby <jsl...@suse.com> Cc: Dmitry Vyukov <dvyu...@google.com> Cc: Johannes Weiner <han...@cmpxchg.org> Cc: Alan Cox <alan@llwyncelyn.cymru> Cc: Christoph Hellwig <h...@lst.de> Cc: Michal Hocko <mho...@suse.com> Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org> [bwh: Backported to 3.16: tty_name() requires a buffer] Signed-off-by: Ben Hutchings <b...@decadent.org.uk> --- drivers/tty/tty_ldisc.c | 13 +++++-------- 1 file changed, 5 insertions(+), 8 deletions(-) --- a/drivers/tty/tty_ldisc.c +++ b/drivers/tty/tty_ldisc.c @@ -510,19 +510,16 @@ static void tty_ldisc_restore(struct tty char buf[64]; /* 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, buf); + + 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, buf)); + panic("Couldn't open N_NULL ldisc for %s.", name); } }
