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

[Greg KH]

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)" */
+#define WDM_DEFAULT_BUFSIZE	256
 
 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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