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Date:   Wed, 17 Apr 2019 13:16:27 +0200
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     syzbot <syzbot+d919b0f29d7b5a4994b9@...kaller.appspotmail.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        LKML <linux-kernel@...r.kernel.org>,
        USB list <linux-usb@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: INFO: task hung in usb_kill_urb

On Tue, Apr 16, 2019 at 8:25 PM Alan Stern <stern@...land.harvard.edu> wrote:
>
> On Tue, 16 Apr 2019, syzbot wrote:
>
> > Hello,
> >
> > syzbot has tested the proposed patch but the reproducer still triggered
> > crash:
> > INFO: task hung in usb_kill_urb
>
> Okay, I think I found the problem.  dummy-hcd doesn't check for
> unsupported speeds until it is too late.  Andrey, what values does your
> usb-fuzzer gadget driver set for its max_speed field?

It's passed from userspace without any validation :( I'll fix this!
Thanks for looking into it!

I wonder why other people saw this hang as well, they didn't use the
dummy hcd module for sure. I guess there are might be other reasons.

>
> Anyway, if I'm right then this patch should fix the bug.
>
> Alan Stern
>
> #syz test: https://github.com/google/kasan.git usb-fuzzer
>
> --- a/drivers/usb/gadget/udc/dummy_hcd.c
> +++ b/drivers/usb/gadget/udc/dummy_hcd.c
> @@ -979,8 +979,18 @@ static int dummy_udc_start(struct usb_ga
>         struct dummy_hcd        *dum_hcd = gadget_to_dummy_hcd(g);
>         struct dummy            *dum = dum_hcd->dum;
>
> -       if (driver->max_speed == USB_SPEED_UNKNOWN)
> +       switch (driver->max_speed) {
> +       /* All the speeds we support */
> +       case USB_SPEED_LOW:
> +       case USB_SPEED_FULL:
> +       case USB_SPEED_HIGH:
> +       case USB_SPEED_SUPER:
> +               break;
> +       default:
> +               dev_err(dummy_dev(dum_hcd), "bogus driver max_speed %d\n",
> +                               driver->max_speed);
>                 return -EINVAL;
> +       }
>
>         /*
>          * SLAVE side init ... the layer above hardware, which
> @@ -1785,7 +1795,8 @@ static void dummy_timer(struct timer_lis
>                 total = 490000;
>                 break;
>         default:
> -               dev_err(dummy_dev(dum_hcd), "bogus device speed\n");
> +               dev_err(dummy_dev(dum_hcd), "bogus device speed %d\n",
> +                               dum->gadget.speed);
>                 return;
>         }
>
>
>

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