Date:	Wed, 04 Jun 2014 10:54:28 -0400
From:	Mike Remski <mremski@...ualink.net>
To:	Johan Hovold <jhovold@...il.com>
CC:	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: ftdi_sio BUG: NULL pointer dereference

On 06/04/2014 10:52 AM, Johan Hovold wrote:
> On Wed, Jun 04, 2014 at 10:29:37AM -0400, Mike Remski wrote:
>> On 06/04/2014 10:19 AM, Johan Hovold wrote:
>>> >From 4ddea3a573b8c15beefb67bc35c440850063d79d Mon Sep 17 00:00:00 2001
>>> From: Johan Hovold <johan@...nel.org>
>>> Date: Wed, 4 Jun 2014 14:09:43 +0200
>>> Subject: [PATCH 1/5] USB: ftdi_sio: fix null deref at port probe
>>>
>>> Fix NULL-pointer dereference when probing an interface with no
>>> endpoints.
>>>
>>> These devices have two bulk endpoints per interface, but this avoids
>>> crashing the kernel if a user forces a non-FTDI device to be probed.
>>>
>>> Note that the iterator variable was made unsigned in order to avoid
>>> a maybe-uninitialized compiler warning for ep_desc after the loop.
>>>
>>> Fixes: 895f28badce9 ("USB: ftdi_sio: fix hi-speed device packet size
>>> calculation")
>>>
>>> Reported-by: Mike Remski <mremski@...ualink.net>
>>> Cc: <stable@...r.kernel.org>	# 2.3.61
>>> Signed-off-by: Johan Hovold <johan@...nel.org>
>>> ---
>>>    drivers/usb/serial/ftdi_sio.c | 7 +++++--
>>>    1 file changed, 5 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/usb/serial/ftdi_sio.c b/drivers/usb/serial/ftdi_sio.c
>>> index 7c6e1dedeb06..3019141397eb 100644
>>> --- a/drivers/usb/serial/ftdi_sio.c
>>> +++ b/drivers/usb/serial/ftdi_sio.c
>>> @@ -1564,14 +1564,17 @@ static void ftdi_set_max_packet_size(struct usb_serial_port *port)
>>>    	struct usb_device *udev = serial->dev;
>>>    
>>>    	struct usb_interface *interface = serial->interface;
>>> -	struct usb_endpoint_descriptor *ep_desc = &interface->cur_altsetting->endpoint[1].desc;
>>> +	struct usb_endpoint_descriptor *ep_desc;
>>>    
>>>    	unsigned num_endpoints;
>>> -	int i;
>>> +	unsigned i;
>>>    
>>>    	num_endpoints = interface->cur_altsetting->desc.bNumEndpoints;
>>>    	dev_info(&udev->dev, "Number of endpoints %d\n", num_endpoints);
>>>    
>>> +	if (!num_endpoints)
>>> +		return;
>>> +
>>>    	/* NOTE: some customers have programmed FT232R/FT245R devices
>>>    	 * with an endpoint size of 0 - not good.  In this case, we
>>>    	 * want to override the endpoint descriptor setting and use a
>> Thanks Johan.  I tried to get the cdc_acm working;  did not have much
>> luck/time (typical overcommit on workload) I will retry with the commit
>> mentioned.
>> I will try the patch today and get back to you.  Nice on the ep_desc:
>> looking at the code priv->max_packet_size is attached to the port, your
>> change would use the last thing off of cur_altsetting->endpoint[], but
>> I'm wondering if we should actually be setting priv->max_packet_size to
>> whatever the max is of all endpoint[].desc->wMaxPacketSize?
>>
>> Thoughts?
> This is the exact same behaviour as the old code (minus the NULL-deref).
>
> These device have two bulk endpoints per interface and they are supposed
> to be using the same max packet size (64 or 512 depending on device and
> host).
>
> This value is also used during depacketisation of incoming data (and
> packetisation of outgoing data for legacy devices). I'm pretty convinced
> you're using the wrong driver, something which would lead to corruption
> of incoming data when the (non-existing) status bytes are stripped from
> the stream.
>
> You really should try cdc-acm.
>
> Johan

Thanks for the explaination.  Yes, I am working on trying cdc-acm.

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