netdev - [PATCH AUTOSEL 4.9 07/13] usbnet: smsc95xx: Fix use-after-free after removal

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Message-Id: <20200702012712.2701986-7-sashal@kernel.org>
Date:   Wed,  1 Jul 2020 21:27:06 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Tuomas Tynkkynen <tuomas.tynkkynen@....fi>,
        syzbot+29dc7d4ae19b703ff947@...kaller.appspotmail.com,
        "David S . Miller" <davem@...emloft.net>,
        Sasha Levin <sashal@...nel.org>, netdev@...r.kernel.org,
        linux-usb@...r.kernel.org
Subject: [PATCH AUTOSEL 4.9 07/13] usbnet: smsc95xx: Fix use-after-free after removal

From: Tuomas Tynkkynen <tuomas.tynkkynen@....fi>

[ Upstream commit b835a71ef64a61383c414d6bf2896d2c0161deca ]

Syzbot reports an use-after-free in workqueue context:

BUG: KASAN: use-after-free in mutex_unlock+0x19/0x40 kernel/locking/mutex.c:737
 mutex_unlock+0x19/0x40 kernel/locking/mutex.c:737
 __smsc95xx_mdio_read drivers/net/usb/smsc95xx.c:217 [inline]
 smsc95xx_mdio_read+0x583/0x870 drivers/net/usb/smsc95xx.c:278
 check_carrier+0xd1/0x2e0 drivers/net/usb/smsc95xx.c:644
 process_one_work+0x777/0xf90 kernel/workqueue.c:2274
 worker_thread+0xa8f/0x1430 kernel/workqueue.c:2420
 kthread+0x2df/0x300 kernel/kthread.c:255

It looks like that smsc95xx_unbind() is freeing the structures that are
still in use by the concurrently running workqueue callback. Thus switch
to using cancel_delayed_work_sync() to ensure the work callback really
is no longer active.

Reported-by: syzbot+29dc7d4ae19b703ff947@...kaller.appspotmail.com
Signed-off-by: Tuomas Tynkkynen <tuomas.tynkkynen@....fi>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/net/usb/smsc95xx.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/usb/smsc95xx.c b/drivers/net/usb/smsc95xx.c
index e719ecd69d01b..6852ebafd4d3b 100644
--- a/drivers/net/usb/smsc95xx.c
+++ b/drivers/net/usb/smsc95xx.c
@@ -1327,7 +1327,7 @@ static void smsc95xx_unbind(struct usbnet *dev, struct usb_interface *intf)
 	struct smsc95xx_priv *pdata = (struct smsc95xx_priv *)(dev->data[0]);
 
 	if (pdata) {
-		cancel_delayed_work(&pdata->carrier_check);
+		cancel_delayed_work_sync(&pdata->carrier_check);
 		netif_dbg(dev, ifdown, dev->net, "free pdata\n");
 		kfree(pdata);
 		pdata = NULL;
-- 
2.25.1