[PATCH 4.19 234/421] mISDN: fix possible use-after-free in HFC_cleanup()

From: Greg Kroah-Hartman
Date: Mon Jul 19 2021 - 12:27:03 EST

From: Zou Wei <zou_wei@xxxxxxxxxx>

[ Upstream commit 009fc857c5f6fda81f2f7dd851b2d54193a8e733 ]

This module's remove path calls del_timer(). However, that function
does not wait until the timer handler finishes. This means that the
timer handler may still be running after the driver's remove function
has finished, which would result in a use-after-free.

Fix by calling del_timer_sync(), which makes sure the timer handler
has finished, and unable to re-schedule itself.

Reported-by: Hulk Robot <hulkci@xxxxxxxxxx>
Signed-off-by: Zou Wei <zou_wei@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
drivers/isdn/hardware/mISDN/hfcpci.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/isdn/hardware/mISDN/hfcpci.c b/drivers/isdn/hardware/mISDN/hfcpci.c
index ebb3fa2e1d00..53349850f866 100644
--- a/drivers/isdn/hardware/mISDN/hfcpci.c
+++ b/drivers/isdn/hardware/mISDN/hfcpci.c
@@ -2348,7 +2348,7 @@ static void __exit
if (timer_pending(&hfc_tl))
- del_timer(&hfc_tl);
+ del_timer_sync(&hfc_tl);