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From: =?utf-8?Q?Bj=C3=B8rn_Mork?= <bjorn@mork.no>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: Jiri Slaby <jslaby@suse.cz>, Vittorio Zecca <zeccav@gmail.com>,
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Subject: Re: UBSAN: Undefined behaviour in linux-4.7.2/drivers/usb/core/devio.c:1713:25
References: <Pine.LNX.4.44L0.1608221337070.5195-100000@iolanthe.rowland.org>
Date: Mon, 22 Aug 2016 22:21:01 +0200
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        (Alan Stern's message of "Mon, 22 Aug 2016 13:43:30 -0400 (EDT)")
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Alan Stern <stern@rowland.harvard.edu> writes:

> On Sun, 21 Aug 2016, Jiri Slaby wrote:
>
>> Cc: proper lists.
>>=20
>> ep->desc.bInterval seems to be 0 here.
>>=20
>> 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
>> >=20
>> > After compiling kernel 4.7.2 with ubsan I got the following messages
>> > at boot time:
>> >=20
>> > (devio.c:1713 is "as->urb->interval =3D 1 << min(15, ep->desc.bInterva=
l - 1);")
>> >=20
>> > [  +0.354486] =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
>> > [  +0.000008] UBSAN: Undefined behaviour in
>> > /home/vitti/1tb/vitti/rpmbuild/SOURCES/linux-4.7.2/drivers/usb/core/de=
vio.c:1713:25
>> > [  +0.000004] shift exponent -1 is negative
>
> As far as I can see, this isn't possible.  The usb_parse_endpoint()=20=20
> 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 =3D stream_id;
        if (uurb->type =3D=3D USBDEVFS_URB_TYPE_ISO ||
                        ps->dev->speed =3D=3D USB_SPEED_HIGH)
                as->urb->interval =3D 1 << min(15, ep->desc.bInterval - 1);
        else
                as->urb->interval =3D ep->desc.bInterval;
        as->urb->context =3D as;



Typo?



Bj=C3=B8rn