linux-kernel - Re: UBSAN: Undefined behaviour in linux-4.7.2/drivers/usb/core/devio.c:1713:25

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Message-ID: <87twecy2qa.fsf@miraculix.mork.no>
Date:   Mon, 22 Aug 2016 22:21:01 +0200
From:   Bjørn Mork <bjorn@...k.no>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     Jiri Slaby <jslaby@...e.cz>, Vittorio Zecca <zeccav@...il.com>,
        <stable@...r.kernel.org>, USB list <linux-usb@...r.kernel.org>,
        Linux kernel mailing list <linux-kernel@...r.kernel.org>
Subject: Re: UBSAN: Undefined behaviour in linux-4.7.2/drivers/usb/core/devio.c:1713:25

Alan Stern <stern@...land.harvard.edu> writes:

> On Sun, 21 Aug 2016, Jiri Slaby wrote:
>
>> Cc: proper lists.
>> 
>> ep->desc.bInterval seems to be 0 here.
>> 
>> On 08/21/2016, 12:42 PM, Vittorio Zecca wrote:
>> > I am not sure this is the right place so please bear with me...
>> > From Vittorio Zecca
>> > 
>> > After compiling kernel 4.7.2 with ubsan I got the following messages
>> > at boot time:
>> > 
>> > (devio.c:1713 is "as->urb->interval = 1 << min(15, ep->desc.bInterval - 1);")
>> > 
>> > [  +0.354486] ================================================================================
>> > [  +0.000008] UBSAN: Undefined behaviour in
>> > /home/vitti/1tb/vitti/rpmbuild/SOURCES/linux-4.7.2/drivers/usb/core/devio.c:1713:25
>> > [  +0.000004] shift exponent -1 is negative
>
> As far as I can see, this isn't possible.  The usb_parse_endpoint()  
> routine in drivers/usb/core/config.c is supposed to guarantee that
> ep->desc.bInterval is never 0.

That is if it is an ISO endpoint, right?

Maybe I misunderstand something fundamental, but the "||" strikes me as
odd here:

        as->urb->stream_id = stream_id;
        if (uurb->type == USBDEVFS_URB_TYPE_ISO ||
                        ps->dev->speed == USB_SPEED_HIGH)
                as->urb->interval = 1 << min(15, ep->desc.bInterval - 1);
        else
                as->urb->interval = ep->desc.bInterval;
        as->urb->context = as;



Typo?



Bjørn