linux-kernel - [PATCH 4.9 48/92] USB: adutux: fix use-after-free on disconnect

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Message-Id: <20191016214835.001785907@linuxfoundation.org>
Date:   Wed, 16 Oct 2019 14:50:21 -0700
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        syzbot+0243cb250a51eeefb8cc@...kaller.appspotmail.com,
        Johan Hovold <johan@...nel.org>
Subject: [PATCH 4.9 48/92] USB: adutux: fix use-after-free on disconnect

From: Johan Hovold <johan@...nel.org>

commit 44efc269db7929f6275a1fa927ef082e533ecde0 upstream.

The driver was clearing its struct usb_device pointer, which it used as
an inverted disconnected flag, before deregistering the character device
and without serialising against racing release().

This could lead to a use-after-free if a racing release() callback
observes the cleared pointer and frees the driver data before
disconnect() is finished with it.

This could also lead to NULL-pointer dereferences in a racing open().

Fixes: f08812d5eb8f ("USB: FIx locks and urb->status in adutux (updated)")
Cc: stable <stable@...r.kernel.org>     # 2.6.24
Reported-by: syzbot+0243cb250a51eeefb8cc@...kaller.appspotmail.com
Tested-by: syzbot+0243cb250a51eeefb8cc@...kaller.appspotmail.com
Signed-off-by: Johan Hovold <johan@...nel.org>
Link: https://lore.kernel.org/r/20190925092913.8608-1-johan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/usb/misc/adutux.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

--- a/drivers/usb/misc/adutux.c
+++ b/drivers/usb/misc/adutux.c
@@ -792,14 +792,15 @@ static void adu_disconnect(struct usb_in
 
 	dev = usb_get_intfdata(interface);
 
-	mutex_lock(&dev->mtx);	/* not interruptible */
-	dev->udev = NULL;	/* poison */
 	usb_deregister_dev(interface, &adu_class);
-	mutex_unlock(&dev->mtx);
 
 	mutex_lock(&adutux_mutex);
 	usb_set_intfdata(interface, NULL);
 
+	mutex_lock(&dev->mtx);	/* not interruptible */
+	dev->udev = NULL;	/* poison */
+	mutex_unlock(&dev->mtx);
+
 	/* if the device is not opened, then we clean up right now */
 	if (!dev->open_count)
 		adu_delete(dev);