HID: fix error message in hid_open_report()

BugLink: https://bugs.launchpad.net/bugs/1851550

commit b3a81c7 upstream.

On HID report descriptor parsing error the code displays bogus
pointer instead of error offset (subtracts start=NULL from end).
Make the message more useful by displaying correct error offset
and include total buffer size for reference.

This was carried over from ancient times - "Fixed" commit just
promoted the message from DEBUG to ERROR.

Cc: [email protected]
Fixes: 8c3d52f ("HID: make parser more verbose about parsing errors by default")
Signed-off-by: Michał Mirosław <[email protected]>
Signed-off-by: Jiri Kosina <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Signed-off-by: Connor Kuehl <[email protected]>
Signed-off-by: Khalid Elmously <[email protected]>

Author: osctobe

drivers/hid/hid-core.c

@@ -1139,6 +1139,7 @@ int hid_open_report(struct hid_device *device)
 	__u8 *start;
 	__u8 *buf;
 	__u8 *end;
+	__u8 *next;
 	int ret;
 	static int (*dispatch_type[])(struct hid_parser *parser,
 				      struct hid_item *item) = {
@@ -1192,7 +1193,8 @@ int hid_open_report(struct hid_device *device)
 	device->collection_size = HID_DEFAULT_NUM_COLLECTIONS;
 
 	ret = -EINVAL;
-	while ((start = fetch_item(start, end, &item)) != NULL) {
+	while ((next = fetch_item(start, end, &item)) != NULL) {
+		start = next;
 
 		if (item.format != HID_ITEM_FORMAT_SHORT) {
 			hid_err(device, "unexpected long global item\n");
@@ -1230,7 +1232,8 @@ int hid_open_report(struct hid_device *device)
 		}
 	}
 
-	hid_err(device, "item fetching failed at offset %d\n", (int)(end - start));
+	hid_err(device, "item fetching failed at offset %u/%u\n",
+		size - (unsigned int)(end - start), size);
 err:
 	kfree(parser->collection_stack);
 alloc_err: