linux-kernel - Re: KASAN: use-after-free Read in si470x_int_in

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Date:   Thu, 28 Nov 2019 11:51:00 +0100
From:   Oliver Neukum <oneukum@...e.com>
To:     Alan Stern <stern@...land.harvard.edu>,
        syzbot <syzbot+9ca7a12fd736d93e0232@...kaller.appspotmail.com>
Cc:     andreyknvl@...gle.com, hverkuil@...all.nl,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
        linux-usb@...r.kernel.org, mchehab@...nel.org,
        syzkaller-bugs@...glegroups.com
Subject: Re: KASAN: use-after-free Read in si470x_int_in_callback (2)

Am Mittwoch, den 27.11.2019, 13:07 -0500 schrieb Alan Stern:
> Index: usb-devel/drivers/media/radio/si470x/radio-si470x-usb.c
> ===================================================================
> --- usb-devel.orig/drivers/media/radio/si470x/radio-si470x-usb.c
> +++ usb-devel/drivers/media/radio/si470x/radio-si470x-usb.c
> @@ -370,15 +370,14 @@ static void si470x_int_in_callback(struc
>         unsigned char tmpbuf[3];
>  
>         if (urb->status) {
> -               if (urb->status == -ENOENT ||
> +               if (!(urb->status == -ENOENT ||
>                                 urb->status == -ECONNRESET ||
> -                               urb->status == -ESHUTDOWN) {
> -                       return;
> -               } else {
> +                               urb->status == -ESHUTDOWN))
>                         dev_warn(&radio->intf->dev,
> -                        "non-zero urb status (%d)\n", urb->status);
> -                       goto resubmit; /* Maybe we can recover. */
> -               }
> +                                       "unrecognized urb status (%d)\n",
> +                                       urb->status);
> +               radio->int_in_running = 0;
> +               return;

Hi,

it is a bit awkward to complain here, as your patch tests as correct
while mine didn't, but this is a race condition.
You can't guarantee that urb->status != 0.
The kill may happen while the completion handler is running for
a successful transfer.

I really appreciate your help, but I must understand what is going
wrong here. You are stopping the resubmit, but how could the resubmit
ever have not failed?

	Regards
		Oliver