linux-kernel - [PATCH (resend)] Input: uinput - Set name/phys to NULL before kfree().

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Message-ID: <b937b59c-22b8-9113-229f-056738819467@I-love.SAKURA.ne.jp>
Date:   Fri, 8 Feb 2019 19:25:52 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     dmitry.torokhov@...il.com, rydberg@...math.org
Cc:     syzbot <syzbot+f648cfb7e0b52bf7ae32@...kaller.appspotmail.com>,
        linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzkaller-bugs@...glegroups.com
Subject: [PATCH (resend)] Input: uinput - Set name/phys to NULL before
 kfree().

syzbot is hitting use-after-free bug in uinput module [1]. This is because
uinput_destroy_device() sometimes kfree()s dev->name and dev->phys at
uinput_destroy_device() before dev_uevent() is triggered by dropping the
refcount to 0. Since the timing of triggering last input_put_device() is
uncontrollable, this patch prepares for such race by setting dev->name and
dev->phys to NULL before doing operations which might drop the refcount
to 0.

[1] https://syzkaller.appspot.com/bug?id=8b17c134fe938bbddd75a45afaa9e68af43a362d

Reported-by: syzbot <syzbot+f648cfb7e0b52bf7ae32@...kaller.appspotmail.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
---
 drivers/input/misc/uinput.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/input/misc/uinput.c b/drivers/input/misc/uinput.c
index 8ec483e8688b..131591b5babd 100644
--- a/drivers/input/misc/uinput.c
+++ b/drivers/input/misc/uinput.c
@@ -300,7 +300,9 @@ static void uinput_destroy_device(struct uinput_device *udev)
 
 	if (dev) {
 		name = dev->name;
+		dev->name = NULL;
 		phys = dev->phys;
+		dev->phys = NULL;
 		if (old_state == UIST_CREATED) {
 			uinput_flush_requests(udev);
 			input_unregister_device(dev);
-- 
2.17.1