linux-kernel - [PATCH 3.16 221/366] tty: Use __GFP_NOFAIL for tty_ldisc

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Date:   Sun, 14 Oct 2018 16:25:41 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Dmitry Vyukov" <dvyukov@...gle.com>,
        "Jiri Slaby" <jslaby@...e.com>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        "Peter Hurley" <peter@...leysoftware.com>,
        "Tetsuo Handa" <penguin-kernel@...ove.SAKURA.ne.jp>,
        "Michal Hocko" <mhocko@...e.com>,
        "Linus Torvalds" <torvalds@...ux-foundation.org>,
        "Vegard Nossum" <vegard.nossum@...il.com>,
        "One Thousand Gnomes" <gnomes@...rguk.ukuu.org.uk>,
        "syzbot" <syzbot+40b7287c2dc987c48c81@...kaller.appspotmail.com>
Subject: [PATCH 3.16 221/366] tty: Use __GFP_NOFAIL for tty_ldisc_get()

3.16.60-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>

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@...ove.SAKURA.ne.jp>
Reported-by: syzbot <syzbot+40b7287c2dc987c48c81@...kaller.appspotmail.com>
Cc: Michal Hocko <mhocko@...e.com>
Cc: Vegard Nossum <vegard.nossum@...il.com>
Cc: Dmitry Vyukov <dvyukov@...gle.com>
Cc: Jiri Slaby <jslaby@...e.com>
Cc: Peter Hurley <peter@...leysoftware.com>
Cc: One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/tty/tty_ldisc.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

--- a/drivers/tty/tty_ldisc.c
+++ b/drivers/tty/tty_ldisc.c
@@ -171,12 +171,11 @@ static struct tty_ldisc *tty_ldisc_get(s
 			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;