linux-kernel - Re: Re: possible deadlock in usb_deregister

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Date:   Tue, 06 Aug 2019 07:22:37 -0700
From:   syzbot <syzbot+a64a382964bf6c71a9c0@...kaller.appspotmail.com>
To:     Oliver Neukum <oneukum@...e.de>
Cc:     andreyknvl@...gle.com, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        oneukum@...e.de, syzkaller-bugs@...glegroups.com
Subject: Re: Re: possible deadlock in usb_deregister_dev

> Am Montag, den 05.08.2019, 04:58 -0700 schrieb syzbot:
>> Hello,

>> syzbot found 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=13b5bc8a600000
>> kernel config:   
>> https://syzkaller.appspot.com/x/.config?x=792eb47789f57810
>> dashboard link:  
>> https://syzkaller.appspot.com/bug?extid=a64a382964bf6c71a9c0
>> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)

>> Unfortunately, I don't have any reproducer for this crash yet.

>> IMPORTANT: if you fix the bug, please add the following tag to the  
>> commit:
>> Reported-by: syzbot+a64a382964bf6c71a9c0@...kaller.appspotmail.com

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

This crash does not have a reproducer. I cannot test it.


>  From 973e82b3f583113e4d7fe5cd2f918a16022c4e38 Mon Sep 17 00:00:00 2001
> From: Oliver Neukum <oneukum@...e.com>
> Date: Tue, 6 Aug 2019 16:17:54 +0200
> Subject: [PATCH] usb: iowarrior: fix deadlock on disconnect

> We have to drop the mutex before we close() upon disconnect()
> as close() needs the lock. This is safe to do by dropping the
> mutex as intfdata is already set to NULL, so open() will fail.

> Fixes: 03f36e885fc26 ("USB: open disconnect race in iowarrior")
> Reported-by: syzbot+a64a382964bf6c71a9c0@...kaller.appspotmail.com
> Signed-off-by: Oliver Neukum <oneukum@...e.com>
> ---
>   drivers/usb/misc/iowarrior.c | 7 ++++---
>   1 file changed, 4 insertions(+), 3 deletions(-)

> diff --git a/drivers/usb/misc/iowarrior.c b/drivers/usb/misc/iowarrior.c
> index ba05dd80a020..f5bed9f29e56 100644
> --- a/drivers/usb/misc/iowarrior.c
> +++ b/drivers/usb/misc/iowarrior.c
> @@ -866,19 +866,20 @@ 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);
> +	/* give back our minor - this will call close() locks need to be  
> dropped at this point*/

> -	/* give back our minor */
>   	usb_deregister_dev(interface, &iowarrior_class);

>   	mutex_lock(&dev->mutex);

>   	/* prevent device read, write and ioctl */
> -	dev->present = 0;

>   	mutex_unlock(&dev->mutex);
> -	mutex_unlock(&iowarrior_open_disc_lock);

>   	if (dev->opened) {
>   		/* There is a process that holds a filedescriptor to the device ,
> --
> 2.16.4