Re: KASAN: use-after-free Read in adu_disconnect

From: Johan Hovold <johan@kernel.org>
To: syzbot <syzbot+0243cb250a51eeefb8cc@syzkaller.appspotmail.com>
Cc: andreyknvl@google.com, dmg@turingmachine.org,
	gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org,
	linux-usb@vger.kernel.org, syzkaller-bugs@googlegroups.com
Subject: Re: KASAN: use-after-free Read in adu_disconnect
Date: Fri, 20 Sep 2019 16:38:55 +0200	[thread overview]
Message-ID: <20190920143855.GS30545@localhost> (raw)
In-Reply-To: <000000000000a12822058fb4f408@google.com>

On Fri, Aug 09, 2019 at 01:24:04PM -0700, syzbot wrote:
> syzbot has found a reproducer for the following crash on:
> 
> HEAD commit:    e96407b4 usb-fuzzer: main usb gadget fuzzer driver
> git tree:       https://github.com/google/kasan.git usb-fuzzer
> console output: https://syzkaller.appspot.com/x/log.txt?x=13871a4a600000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=cfa2c18fb6a8068e
> dashboard link: https://syzkaller.appspot.com/bug?extid=0243cb250a51eeefb8cc
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11c4c8e2600000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11d80d2c600000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+0243cb250a51eeefb8cc@syzkaller.appspotmail.com
> 
> usb 1-1: USB disconnect, device number 4
> ==================================================================
> BUG: KASAN: use-after-free in atomic64_read  
> include/asm-generic/atomic-instrumented.h:836 [inline]
> BUG: KASAN: use-after-free in atomic_long_read  
> include/asm-generic/atomic-long.h:28 [inline]
> BUG: KASAN: use-after-free in __mutex_unlock_slowpath+0x96/0x670  
> kernel/locking/mutex.c:1211
> Read of size 8 at addr ffff8881d1d0aa00 by task kworker/0:1/12

Let's resend and retest using the latest usb-fuzzer kernel, which
includes the fix for a couple char dev races that we were now hitting:

#syz test: https://github.com/google/kasan.git e0bd8d79

I'll fix the failure to stop I/O at disconnect separately.

Johan


From 6f09430ae18085a1552fc641e53d3a3e678db6f3 Mon Sep 17 00:00:00 2001
From: Johan Hovold <johan@kernel.org>
Date: Thu, 19 Sep 2019 11:48:38 +0200
Subject: [PATCH] USB: adutux: fix use-after-free on disconnect

The driver was clearing its struct usb_device pointer, which it uses 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)")
Reported-by: syzbot+0243cb250a51eeefb8cc@syzkaller.appspotmail.com
Cc: stable <stable@vger.kernel.org>     # 2.6.24
Signed-off-by: Johan Hovold <johan@kernel.org>
---

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

diff --git a/drivers/usb/misc/adutux.c b/drivers/usb/misc/adutux.c
index 344d523b0502..bcc138990e2f 100644
--- a/drivers/usb/misc/adutux.c
+++ b/drivers/usb/misc/adutux.c
@@ -762,14 +762,15 @@ static void adu_disconnect(struct usb_interface *interface)
 
 	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);
-- 
2.23.0

