linux-kernel - Re: ftdi_sio BUG: NULL pointer dereference

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Message-ID: <20140602174630.GD13790@localhost>
Date:	Mon, 2 Jun 2014 19:46:30 +0200
From:	Johan Hovold <jhovold@...il.com>
To:	Mike Remski <mremski@...ualink.net>
Cc:	Johan Hovold <jhovold@...il.com>, linux-kernel@...r.kernel.org,
	linux-usb@...r.kernel.org
Subject: Re: ftdi_sio BUG: NULL pointer dereference

On Mon, Jun 02, 2014 at 01:11:37PM -0400, Mike Remski wrote:
> On 06/02/2014 12:49 PM, Johan Hovold wrote:
> > On Mon, Jun 02, 2014 at 12:24:44PM -0400, Mike Remski wrote:
> >> On 06/02/2014 12:20 PM, Johan Hovold wrote:
> >>> On Mon, Jun 02, 2014 at 12:02:40PM -0400, Mike Remski wrote:
> >>>> On 06/02/2014 11:40 AM, Johan Hovold wrote:
> >>>>> [ Please avoid top-posting. ]
> >>>>>
> >>>>> On Mon, Jun 02, 2014 at 11:16:11AM -0400, Mike Remski wrote:

> >>> The third interface lacks endpoints and crashes the ftdi_sio driver.
> >>> This shouldn't happen (even if you're forcing the wrong driver to bind),
> >>> so I'll fix it up if still broken in v3.15-rc.
> >>>
> >> Johan,
> >> Thanks again.  Yes, the device does indeed have an FTDI embedded in it;
> >> they've programmed in their own ids.  They supply a Windows driver for
> >> it, but that doesn't do me any good.  :)
> > Not just their own ID's it seems.
> >
> > Have you tried just using the cdc-acm driver? The ports should up as
> > /dev/ttyACMx instead of ttyUSBx.
> >
> Not yet, next on the list.

You really should try this before anything else. :)

> I'm suspecting that bNumEndpoints == 0 is causing endpoint[1].desc to 
> stay at NULL (line 1567 in 3.1.4.5 source), so by the time it gets used 
> later on, I'm hitting the NULL dereference.

Yeah, the code is obviously broken (also in v3.15-rc). It should
probably work to just return from ftdi_set_max_packet_size if
num_endpoints is 0 if you want to try that (or you can use your ?:
construct), but I should be able to fix this up properly on Wednesday.

Thanks,
Johan
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