[Qemu-devel] [PATCH v2] Guest OS hangs on usb_add

[TJ <one.timothy.jones@gmail.com>]

This is a small patch to sligtly "intelligentify" usb device and
config descriptor parsing and to handle bug with certain usb
device (URC MX-950) reporting device desriptor length as 0x18
instead of 18 with added vendor_id/product_id check
---
 hw/usb.h    |    5 +++++
 usb-linux.c |   37 ++++++++++++++++++++++---------------
 2 files changed, 27 insertions(+), 15 deletions(-)

diff --git a/hw/usb.h b/hw/usb.h
index 00d2802..5c3528f 100644
--- a/hw/usb.h
+++ b/hw/usb.h
@@ -117,6 +117,11 @@
 #define USB_DT_INTERFACE		0x04
 #define USB_DT_ENDPOINT			0x05

+#define USB_DT_DEVICE_LEN		18
+#define USB_DT_CONFIG_LEN		9
+#define USB_DT_INTERFACE_LEN		9
+#define USB_DT_ENDPOINT_LEN		7
+
 #define USB_ENDPOINT_XFER_CONTROL	0
 #define USB_ENDPOINT_XFER_ISOC		1
 #define USB_ENDPOINT_XFER_BULK		2
diff --git a/usb-linux.c b/usb-linux.c
index 88273ff..2ac6562 100644
--- a/usb-linux.c
+++ b/usb-linux.c
@@ -288,7 +288,7 @@ static void async_cancel(USBPacket *unused, void *opaque)

 static int usb_host_claim_interfaces(USBHostDevice *dev, int configuration)
 {
-    int dev_descr_len, config_descr_len;
+    int dev_descr_len, config_descr_total_len;
     int interface, nb_interfaces;
     int ret, i;

@@ -297,32 +297,39 @@ static int usb_host_claim_interfaces(USBHostDevice *dev,
int configuration)

     DPRINTF("husb: claiming interfaces. config %d\n", configuration);

-    i = 0;
     dev_descr_len = dev->descr[0];
-    if (dev_descr_len > dev->descr_len) {
+    if (dev_descr_len == 0x18 && dev->descr[ 8] == 0x47 && dev->descr[ 9] == 0x46
+                              && dev->descr[10] == 0x00 && dev->descr[11] == 0x30)
+        dev_descr_len = USB_DT_DEVICE_LEN; /* for buggy MX-950 remote reporting
len in hex */
+
+    if (dev_descr_len > dev->descr_len || dev_descr_len < USB_DT_DEVICE_LEN ||
dev->descr[1] != USB_DT_DEVICE) {
+        fprintf(stderr, "husb: invalid device descriptor\n");
         goto fail;
     }

-    i += dev_descr_len;
-    while (i < dev->descr_len) {
+    for (i = dev_descr_len; i < dev->descr_len; ) {
         DPRINTF("husb: i is %d, descr_len is %d, dl %d, dt %d\n",
                 i, dev->descr_len,
                dev->descr[i], dev->descr[i+1]);

-        if (dev->descr[i+1] != USB_DT_CONFIG) {
-            i += dev->descr[i];
-            continue;
+        if (dev->descr[i] < 2) {
+            fprintf(stderr, "husb: invalid descriptor\n");
+            goto fail;
         }
-        config_descr_len = dev->descr[i];
+        if (dev->descr[i+1] == USB_DT_CONFIG) {
+            config_descr_total_len = dev->descr[i+2] + (dev->descr[i+3] << 8);

-        printf("husb: config #%d need %d\n", dev->descr[i + 5], configuration);
+            printf("husb: config #%d need %d\n", dev->descr[i + 5], configuration);

-        if (configuration < 0 || configuration == dev->descr[i + 5]) {
-            configuration = dev->descr[i + 5];
-            break;
-        }
+            if (configuration < 0 || configuration == dev->descr[i + 5]) {
+                configuration = dev->descr[i + 5];
+                break;
+            }

-        i += config_descr_len;
+            i += config_descr_total_len;
+        }
+        else
+            i += dev->descr[i];
     }

     if (i >= dev->descr_len) {