[PATCH 4.4 098/188] atm: nicstar: Fix possible use-after-free in nicstar_cleanup()

From: Greg Kroah-Hartman
Date: Mon Jul 19 2021 - 11:00:58 EST

From: Zou Wei <zou_wei@xxxxxxxxxx>

[ Upstream commit 34e7434ba4e97f4b85c1423a59b2922ba7dff2ea ]

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/atm/nicstar.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/atm/nicstar.c b/drivers/atm/nicstar.c
index 49da83f87170..486d7a114031 100644
--- a/drivers/atm/nicstar.c
+++ b/drivers/atm/nicstar.c
@@ -298,7 +298,7 @@ static void __exit nicstar_cleanup(void)
XPRINTK("nicstar: nicstar_cleanup() called.\n");

- del_timer(&ns_timer);
+ del_timer_sync(&ns_timer);