linux-kernel - [PATCH 4.13 087/109] media: Revert "[media] lirc_dev: remove superfluous get/put

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Message-Id: <20170924203356.598563074@linuxfoundation.org>
Date:   Sun, 24 Sep 2017 22:33:48 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Sean Young <sean@...s.org>,
        Mauro Carvalho Chehab <mchehab@...pensource.com>
Subject: [PATCH 4.13 087/109] media: Revert "[media] lirc_dev: remove superfluous get/put_device() calls"

4.13-stable review patch.  If anyone has any objections, please let me know.

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

From: Sean Young <sean@...s.org>

commit a607f51e5a4c421e2097077db88105402099c528 upstream.

This reverts commit 5be2b76a9ca4ea5fd3e221114d62eeb0d78267ca.

Only when the lirc device is freed, should we drop our reference to
rc_dev, else we the rc_dev is freed to early. If userspace has
a file descriptor open during unplug, it goes bang.

==================================================================
BUG: KASAN: use-after-free in __lock_acquire+0x7bb/0x1e10
Read of size 8 at addr ffff8801d7d61ed0 by task ir-rec/2609

-snip-
 mutex_lock_nested+0x1b/0x20
 ? mutex_lock_nested+0x1b/0x20
 rc_close.part.6+0x20/0x60 [rc_core]
 rc_close+0x13/0x20 [rc_core]
 lirc_dev_fop_close+0x62/0xd0 [lirc_dev]
 __fput+0x236/0x410
 ? fput+0xb0/0xb0
 ? do_raw_spin_trylock+0x110/0x110
 ? set_rq_offline.part.70+0xa0/0xa0
 ____fput+0xe/0x10
 task_work_run+0x116/0x180
 ? task_work_cancel+0x170/0x170
 ? _raw_spin_unlock+0x27/0x40
 ? switch_task_namespaces+0x5f/0x90
 do_exit+0x68b/0xe80

Fixes: 5be2b76a9ca4 ("[media] lirc_dev: remove superfluous get/put_device() calls")
Signed-off-by: Sean Young <sean@...s.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@...pensource.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/media/rc/lirc_dev.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/drivers/media/rc/lirc_dev.c
+++ b/drivers/media/rc/lirc_dev.c
@@ -59,6 +59,8 @@ static void lirc_release(struct device *
 {
 	struct irctl *ir = container_of(ld, struct irctl, dev);
 
+	put_device(ir->dev.parent);
+
 	if (ir->buf_internal) {
 		lirc_buffer_free(ir->buf);
 		kfree(ir->buf);
@@ -218,6 +220,8 @@ int lirc_register_driver(struct lirc_dri
 
 	mutex_unlock(&lirc_dev_lock);
 
+	get_device(ir->dev.parent);
+
 	dev_info(ir->d.dev, "lirc_dev: driver %s registered at minor = %d\n",
 		 ir->d.name, ir->d.minor);