[PATCH 001/001]: USB: cdc_acm: Fix oops when Droids MuIn LCD is connected

[Erik Slagter <erik@slagter.name>]

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From: Erik Slagter <erik@slagter.name>

The Droids MuIn LCD operates like a serial remote terminal.
Data received are displayed directly on the LCD. This patch
fixes the kernel null pointer oops when it is plugged in.

Add NO_DATA_INTERFACE quirk to tell the driver that "control"
and "data" interfaces are not separated for this device, which
prevents dereferencing a null pointer in the device probe code.

Signed-off-by: Erik Slagter <erik@slagter.name>
Signed-off-by: Maxin B. John <maxin.john@gmail.com>
Tested-by: Erik Slagter <erik@slagter.name>
---
This patch applies to vanilla kernel 2.6.38.2, but I am quite
confident it will apply to any recent kernel. It was created by
Maxin John after I located the problem, slightly modified by me
and tested by me, so blame me if it breaks anything.

diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
index e057e53..caa2535 100644
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -946,7 +946,7 @@ static int acm_probe(struct usb_interface *intf,
 	u8 ac_management_function = 0;
 	u8 call_management_function = 0;
 	int call_interface_num = -1;
-	int data_interface_num;
+	int data_interface_num = -1;
 	unsigned long quirks;
 	int num_rx_buf;
 	int i;
@@ -1030,7 +1030,11 @@ next_desc:
 	if (!union_header) {
 		if (call_interface_num > 0) {
 			dev_dbg(&intf->dev, "No union descriptor, using call management descriptor\n");
-			data_interface = usb_ifnum_to_if(usb_dev, (data_interface_num = call_interface_num));
+			/* quirks for Droids MuIn LCD */
+			if (quirks & NO_DATA_INTERFACE)
+				data_interface = usb_ifnum_to_if(usb_dev, 0);
+			else
+				data_interface = usb_ifnum_to_if(usb_dev, (data_interface_num = call_interface_num));
 			control_interface = intf;
 		} else {
 			if (intf->cur_altsetting->desc.bNumEndpoints != 3) {
@@ -1622,6 +1626,11 @@ static const struct usb_device_id acm_ids[] = {
 	.driver_info = NOT_A_MODEM,
 	},

+	/* Support for Droids MuIn LCD */
+	{ USB_DEVICE(0x04d8, 0x000b),
+	.driver_info = NO_DATA_INTERFACE,
+	},
+
 	/* control interfaces without any protocol set */
 	{ USB_INTERFACE_INFO(USB_CLASS_COMM, USB_CDC_SUBCLASS_ACM,
 		USB_CDC_PROTO_NONE) },
diff --git a/drivers/usb/class/cdc-acm.h b/drivers/usb/class/cdc-acm.h
index b4ea54d..683104a 100644
--- a/drivers/usb/class/cdc-acm.h
+++ b/drivers/usb/class/cdc-acm.h
@@ -137,3 +137,4 @@ struct acm {
 #define SINGLE_RX_URB			2
 #define NO_CAP_LINE			4
 #define NOT_A_MODEM			8
+#define NO_DATA_INTERFACE		16



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