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

From: Greg Kroah-Hartman
Date: Sun Jun 09 2019 - 13:16:32 EST

[ 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@xxxxxxxxx>
Signed-off-by: Alexandre Belloni <alexandre.belloni@xxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
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);

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