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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Hulk Robot <hulkci@huawei.com>,
        Zou Wei <zou_wei@huawei.com>,
        "David S. Miller" <davem@davemloft.net>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 4.9 128/245] atm: nicstar: Fix possible use-after-free in nicstar_cleanup()
Date:   Mon, 19 Jul 2021 16:51:10 +0200
Message-Id: <20210719144944.543748013@linuxfoundation.org>
In-Reply-To: <20210719144940.288257948@linuxfoundation.org>
References: <20210719144940.288257948@linuxfoundation.org>
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From: Zou Wei <zou_wei@huawei.com>

[ 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@huawei.com>
Signed-off-by: Zou Wei <zou_wei@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 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 8bcd09fb0feb..b2bae94ffe4d 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);
 
 	pci_unregister_driver(&nicstar_driver);
 
-- 
2.30.2