tty: Use __GFP_NOFAIL for tty_ldisc_get()

BugLink: http://bugs.launchpad.net/bugs/1778265
commit bcdd0ca8cb8730573afebcaae4138f8f4c8eaa20 upstream.

syzbot is reporting crashes triggered by memory allocation fault injection
at tty_ldisc_get() [1]. As an attempt to handle OOM in a graceful way, we
have tried commit 5362544bebe85071 ("tty: don't panic on OOM in
tty_set_ldisc()"). But we reverted that attempt by commit a8983d01f9b7d600
("Revert "tty: don't panic on OOM in tty_set_ldisc()"") due to reproducible
crash. We should spend resource for finding and fixing race condition bugs
rather than complicate error paths for 2 * sizeof(void *) bytes allocation
failure.

[1] https://syzkaller.appspot.com/bug?id=489d33fa386453859ead58ff5171d43772b13aa3

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reported-by: syzbot <syzbot+40b7287c2dc987c48c81@syzkaller.appspotmail.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Vegard Nossum <vegard.nossum@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Jiri Slaby <jslaby@suse.com>
Cc: Peter Hurley <peter@hurleysoftware.com>
Cc: One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
index 229fa7ec0464d5708842094e6caed833b837c174..0fd18f5fa67d34061634f63ce6dc1c16d91dbbb7 100644 (file)
--- a/drivers/tty/tty_ldisc.c
+++ b/drivers/tty/tty_ldisc.c
@@ -176,12 +176,11 @@ static struct tty_ldisc *tty_ldisc_get(struct tty_struct *tty, int disc)
                        return ERR_CAST(ldops);
        }
 
-       ld = kmalloc(sizeof(struct tty_ldisc), GFP_KERNEL);
-       if (ld == NULL) {
-               put_ldops(ldops);
-               return ERR_PTR(-ENOMEM);
-       }
-
+       /*
+        * There is no way to handle allocation failure of only 16 bytes.
+        * Let's simplify error handling and save more memory.
+        */
+       ld = kmalloc(sizeof(struct tty_ldisc), GFP_KERNEL | __GFP_NOFAIL);
        ld->ops = ldops;
        ld->tty = tty;