[68/89] USB: cdc-wdm: Avoid hanging on interface with no USB_CDC_DMM_TYPE

From: Greg KH
Date: Wed Feb 01 2012 - 16:20:55 EST

3.2-stable review patch. If anyone has any objections, please let me know.


From: Bjørn Mork <bjorn@xxxxxxx>

commit 15699e6fafc3a90e5fdc2ef30555a04dee62286f upstream.

The probe does not strictly require the USB_CDC_DMM_TYPE
descriptor, which is a good thing as it makes the driver
usable on non-conforming interfaces. A user could e.g.
bind to it to a CDC ECM interface by using the new_id and
bind sysfs files. But this would fail with a 0 buffer length
due to the missing descriptor.

Fix by defining a reasonable fallback size: The minimum
device receive buffer size required by the CDC WMC standard,
revision 1.1

Signed-off-by: Bjørn Mork <bjorn@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

drivers/usb/class/cdc-wdm.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

--- a/drivers/usb/class/cdc-wdm.c
+++ b/drivers/usb/class/cdc-wdm.c
@@ -57,6 +57,8 @@ MODULE_DEVICE_TABLE (usb, wdm_ids);

#define WDM_MAX 16

+/* CDC-WMC r1.1 requires wMaxCommand to be "at least 256 decimal (0x100)" */

static DEFINE_MUTEX(wdm_mutex);

@@ -636,7 +638,7 @@ static int wdm_probe(struct usb_interfac
struct usb_cdc_dmm_desc *dmhd;
u8 *buffer = intf->altsetting->extra;
int buflen = intf->altsetting->extralen;
- u16 maxcom = 0;
+ u16 maxcom = WDM_DEFAULT_BUFSIZE;

if (!buffer)
goto out;

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