linux-kernel - Re: usb/gadget: stalls in dummy

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Date:   Tue, 19 Sep 2017 15:17:13 +0200
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Henrik Rydberg <rydberg@...math.org>,
        "linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
        Felipe Balbi <balbi@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Johan Hovold <johan@...nel.org>,
        Peter Chen <peter.chen@....com>,
        Yuyang Du <yuyang.du@...el.com>,
        USB list <linux-usb@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: usb/gadget: stalls in dummy_timer

On Fri, Sep 15, 2017 at 8:57 PM, Alan Stern <stern@...land.harvard.edu> wrote:
> On Thu, 14 Sep 2017, Andrey Konovalov wrote:
>
>> On Thu, Sep 14, 2017 at 7:49 PM, Alan Stern <stern@...land.harvard.edu> wrote:
>> > On Thu, 14 Sep 2017, Andrey Konovalov wrote:
>> >
>> >> Looked at this a little more.
>> >>
>> >> dummy_timer() stucks in an infinite loop. It calls
>> >> usb_hcd_giveback_urb(), which in turn calls usbtouch_irq(), which
>> >> calls usb_submit_urb(), which calls dummy_urb_enqueue() and puts urb
>> >> back into dummy urb queue. dummy_timer() then does goto restart, finds
>> >> the urb and calls usb_hcd_giveback_urb() again. And this process goes
>> >> on again and again. It seems that something should either process the
>> >> urb and set urb->status or it should just expire.
>> >
>> > There is some throttling code, but it applies only to bulk transfers.
>> > Probably because the bandwidth limits for other types are slightly
>> > different.  However, I don't think we need to worry about this level of
>> > detail, since the driver makes a number of other approximations anyway.
>> >
>> > Try the patch below; it should fix the problem.
>>
>> Hi Alan,
>>
>> Just tried your patch, my reproducer still hangs the kernel until all
>> memory is exhausted.
>>
>> Thanks!
>
> Hmmm.  Your reproducer doesn't run on my system.  The mmap system call
> fails, perhaps because this laptop has a 32-bit kernel.  So I can't
> tell what's going on.
>
> Can you collect a usbmon trace that shows what happens while the
> reproducer runs?  If it turns out to be extremely large, just post an
> initial portion of it.

I've attached the usbmon trace. It's actually quite short, probably
due to the fact that the kernel enters infinite loop.

I've also attached a reproducer that should compile on a 32 bit
system, however I haven't tested whether it reproduces the issue.

>
> Alan Stern
>

Download attachment "dummy_timer-stall-usbmon" of type "application/octet-stream" (3154 bytes)

View attachment "usbtouchscreen-hang-poc-x32.c" of type "text/x-csrc" (7297 bytes)