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

From Alan Stern <stern@rowland.harvard.edu>
Newsgroups linux.kernel
Subject Re: UBSAN: Undefined behaviour in linux-4.7.2/drivers/usb/core/devio.c:1713:25
Date 2016-08-22 19:50 +0200
Message-ID <s91we-Tx-13@gated-at.bofh.it> (permalink)
References <s8yud-7DA-7@gated-at.bofh.it>
Organization linux.* mail to news gateway

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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

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Re: UBSAN: Undefined behaviour in  linux-4.7.2/drivers/usb/core/devio.c:1713:25 Jiri Slaby <jslaby@suse.cz> - 2016-08-21 12:50 +0200
  Re: UBSAN: Undefined behaviour in linux-4.7.2/drivers/usb/core/devio.c:1713:25 Alan Stern <stern@rowland.harvard.edu> - 2016-08-22 19:50 +0200
    Re: UBSAN: Undefined behaviour in linux-4.7.2/drivers/usb/core/devio.c:1713:25 Bjørn Mork <bjorn@mork.no> - 2016-08-22 22:30 +0200
      Re: UBSAN: Undefined behaviour in linux-4.7.2/drivers/usb/core/devio.c:1713:25 Alan Stern <stern@rowland.harvard.edu> - 2016-08-22 22:50 +0200
        Re: UBSAN: Undefined behaviour in linux-4.7.2/drivers/usb/core/devio.c:1713:25 Bjørn Mork <bjorn@mork.no> - 2016-08-22 23:00 +0200
          Re: UBSAN: Undefined behaviour in linux-4.7.2/drivers/usb/core/devio.c:1713:25 Alan Stern <stern@rowland.harvard.edu> - 2016-08-22 23:10 +0200
            Re: UBSAN: Undefined behaviour in linux-4.7.2/drivers/usb/core/devio.c:1713:25 Vittorio Zecca <zeccav@gmail.com> - 2016-08-22 23:50 +0200
              Re: UBSAN: Undefined behaviour in linux-4.7.2/drivers/usb/core/devio.c:1713:25 Alan Stern <stern@rowland.harvard.edu> - 2016-08-23 17:10 +0200
                Re: UBSAN: Undefined behaviour in linux-4.7.2/drivers/usb/core/devio.c:1713:25 Vittorio Zecca <zeccav@gmail.com> - 2016-08-23 18:00 +0200
                Re: UBSAN: Undefined behaviour in linux-4.7.2/drivers/usb/core/devio.c:1713:25 Alan Stern <stern@rowland.harvard.edu> - 2016-08-23 21:00 +0200

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