From: Bjørn Mork <bjorn@mork.no>
Date: Fri, 20 Jan 2012 00:49:57 +0000 (+0100)
Subject: USB: cdc-wdm: Avoid hanging on interface with no USB_CDC_DMM_TYPE
X-Git-Tag: v3.4-rc1~184^2~22^2~121^2~21
X-Git-Url: http://git.cascardo.eti.br/?a=commitdiff_plain;h=7e3054a005537f28544ab2870c375458362f7473;p=cascardo%2Flinux.git

USB: cdc-wdm: Avoid hanging on interface with no USB_CDC_DMM_TYPE

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@mork.no>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
---

diff --git a/drivers/usb/class/cdc-wdm.c b/drivers/usb/class/cdc-wdm.c
index bb8208a13a53..c0197af22fd8 100644
--- 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);
 
@@ -602,7 +604,7 @@ static int wdm_probe(struct usb_interface *intf, const struct usb_device_id *id)
 	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;