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SubjectRe: Re: possible deadlock in usb_deregister_dev
From
> 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@syzkaller.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@suse.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@syzkaller.appspotmail.com
> Signed-off-by: Oliver Neukum <oneukum@suse.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

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