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

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Message-ID: <Pine.LNX.4.44L0.1608221337070.5195-100000@iolanthe.rowland.org>
Date:   Mon, 22 Aug 2016 13:43:30 -0400 (EDT)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Jiri Slaby <jslaby@...e.cz>
cc:     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

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.

More information from Vittorio would be helpful.  For example, what 
shows up in /sys/kernel/debug/usb/devices (after mounting a debugfs 
filesystem on /sys/kernel/debug)?

Alan Stern