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

Should be fixed by the below patch.

#syz test: https://github.com/google/kasan.git f0df5c1b

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
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