linux-kernel - [PATCH 1/6] USB: iowarrior: fix use-after-free on disconnect

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Date:   Wed,  9 Oct 2019 12:48:41 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Oliver Neukum <oneukum@...e.com>,
        Valentin Vidic <vvidic@...entin-vidic.from.hr>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Johan Hovold <johan@...nel.org>,
        stable <stable@...r.kernel.org>,
        syzbot+0761012cebf7bdb38137@...kaller.appspotmail.com
Subject: [PATCH 1/6] USB: iowarrior: fix use-after-free on disconnect

A recent fix addressing a deadlock on disconnect introduced a new bug
by moving the present flag out of the critical section protected by the
driver-data mutex. This could lead to a racing release() freeing the
driver data before disconnect() is done with it.

Due to insufficient locking a related use-after-free could be triggered
also before the above mentioned commit. Specifically, the driver needs
to hold the driver-data mutex also while checking the opened flag at
disconnect().

Fixes: c468a8aa790e ("usb: iowarrior: fix deadlock on disconnect")
Fixes: 946b960d13c1 ("USB: add driver for iowarrior devices.")
Cc: stable <stable@...r.kernel.org>	# 2.6.21
Reported-by: syzbot+0761012cebf7bdb38137@...kaller.appspotmail.com
Signed-off-by: Johan Hovold <johan@...nel.org>
---
 drivers/usb/misc/iowarrior.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/usb/misc/iowarrior.c b/drivers/usb/misc/iowarrior.c
index f5bed9f29e56..4fe1d3267b3c 100644
--- a/drivers/usb/misc/iowarrior.c
+++ b/drivers/usb/misc/iowarrior.c
@@ -866,8 +866,6 @@ static void iowarrior_disconnect(struct usb_interface *interface)
 	dev = usb_get_intfdata(interface);
 	mutex_lock(&iowarrior_open_disc_lock);
 	usb_set_intfdata(interface, NULL);
-	/* prevent device read, write and ioctl */
-	dev->present = 0;
 
 	minor = dev->minor;
 	mutex_unlock(&iowarrior_open_disc_lock);
@@ -878,8 +876,7 @@ static void iowarrior_disconnect(struct usb_interface *interface)
 	mutex_lock(&dev->mutex);
 
 	/* prevent device read, write and ioctl */
-
-	mutex_unlock(&dev->mutex);
+	dev->present = 0;
 
 	if (dev->opened) {
 		/* There is a process that holds a filedescriptor to the device ,
@@ -889,8 +886,10 @@ static void iowarrior_disconnect(struct usb_interface *interface)
 		usb_kill_urb(dev->int_in_urb);
 		wake_up_interruptible(&dev->read_wait);
 		wake_up_interruptible(&dev->write_wait);
+		mutex_unlock(&dev->mutex);
 	} else {
 		/* no process is using the device, cleanup now */
+		mutex_unlock(&dev->mutex);
 		iowarrior_delete(dev);
 	}
 
-- 
2.23.0