linux-kernel - [PATCH 4.4 100/241] rtc: 88pm860x: prevent use-after-free on device remove

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Date:   Sun,  9 Jun 2019 18:40:42 +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, Sven Van Asbroeck <TheSven73@...il.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.4 100/241] rtc: 88pm860x: prevent use-after-free on device remove

[ Upstream commit f22b1ba15ee5785aa028384ebf77dd39e8e47b70 ]

The device's remove() attempts to shut down the delayed_work scheduled
on the kernel-global workqueue by calling flush_scheduled_work().

Unfortunately, flush_scheduled_work() does not prevent the delayed_work
from re-scheduling itself. The delayed_work might run after the device
has been removed, and touch the already de-allocated info structure.
This is a potential use-after-free.

Fix by calling cancel_delayed_work_sync() during remove(): this ensures
that the delayed work is properly cancelled, is no longer running, and
is not able to re-schedule itself.

This issue was detected with the help of Coccinelle.

Signed-off-by: Sven Van Asbroeck <TheSven73@...il.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@...tlin.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/rtc/rtc-88pm860x.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/rtc/rtc-88pm860x.c b/drivers/rtc/rtc-88pm860x.c
index 19e53b3b8e005..166faae3a59cd 100644
--- a/drivers/rtc/rtc-88pm860x.c
+++ b/drivers/rtc/rtc-88pm860x.c
@@ -414,7 +414,7 @@ static int pm860x_rtc_remove(struct platform_device *pdev)
 	struct pm860x_rtc_info *info = platform_get_drvdata(pdev);

 #ifdef VRTC_CALIBRATION
-	flush_scheduled_work();
+	cancel_delayed_work_sync(&info->calib_work);
 	/* disable measurement */
 	pm860x_set_bits(info->i2c, PM8607_MEAS_EN2, MEAS2_VRTC, 0);
 #endif	/* VRTC_CALIBRATION */
-- 
2.20.1