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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, Duoming Zhou <duoming@zju.edu.cn>,
        Jakub Kicinski <kuba@kernel.org>
Subject: [PATCH 4.19 243/287] atm: idt77252: fix use-after-free bugs caused by tst_timer
Date:   Tue, 23 Aug 2022 10:26:52 +0200
Message-Id: <20220823080109.291866469@linuxfoundation.org>
In-Reply-To: <20220823080100.268827165@linuxfoundation.org>
References: <20220823080100.268827165@linuxfoundation.org>
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From: Duoming Zhou <duoming@zju.edu.cn>

commit 3f4093e2bf4673f218c0bf17d8362337c400e77b upstream.

There are use-after-free bugs caused by tst_timer. The root cause
is that there are no functions to stop tst_timer in idt77252_exit().
One of the possible race conditions is shown below:

    (thread 1)          |        (thread 2)
                        |  idt77252_init_one
                        |    init_card
                        |      fill_tst
                        |        mod_timer(&card->tst_timer, ...)
idt77252_exit           |  (wait a time)
                        |  tst_timer
                        |
                        |    ...
  kfree(card) // FREE   |
                        |    card->soft_tst[e] // USE

The idt77252_dev is deallocated in idt77252_exit() and used in
timer handler.

This patch adds del_timer_sync() in idt77252_exit() in order that
the timer handler could be stopped before the idt77252_dev is
deallocated.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
Link: https://lore.kernel.org/r/20220805070008.18007-1-duoming@zju.edu.cn
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/atm/idt77252.c |    1 +
 1 file changed, 1 insertion(+)

--- a/drivers/atm/idt77252.c
+++ b/drivers/atm/idt77252.c
@@ -3767,6 +3767,7 @@ static void __exit idt77252_exit(void)
 		card = idt77252_chain;
 		dev = card->atmdev;
 		idt77252_chain = card->next;
+		del_timer_sync(&card->tst_timer);
 
 		if (dev->phy->stop)
 			dev->phy->stop(dev);