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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

    Let's resend and retest with commit id from latest report to make sure
    the patch was actually applied during the last run:

    #syz test: https://github.com/google/kasan.git e96407b4

    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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