[PATCH 5.7 014/112] usbnet: smsc95xx: Fix use-after-free after removal

Greg Kroah-Hartman
2020-07-07T15:22:56Z

From: Tuomas Tynkkynen <tuomas.tynkkynen@iki.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is no longer active.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@syzkaller.appspotmail.com
Signed-off-by: Tuomas Tynkkynen <tuomas.tynkkynen@iki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.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 355be77f42418..3cf4dc3433f91 100644
--- a/drivers/net/usb/smsc95xx.c
+++ b/drivers/net/usb/smsc95xx.c
@@ -1324,7 +1324,7 @@ 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