HID: uhid: make creating devices work on 64/32 systems

Unfortunately UHID interface, as it was introduced, is broken with 32 bit
userspace running on 64 bit kernels as it uses a pointer in its userspace
facing API.

Fix it by checking if we are executing compat task and munge the request
appropriately.
Reported-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/uhid.c

@@ -11,6 +11,7 @@
  */
 
 #include <linux/atomic.h>
+#include <linux/compat.h>
 #include <linux/device.h>
 #include <linux/fs.h>
 #include <linux/hid.h>
@@ -276,6 +277,94 @@ static struct hid_ll_driver uhid_hid_driver = {
 	.parse = uhid_hid_parse,
 };
 
+#ifdef CONFIG_COMPAT
+
+/* Apparently we haven't stepped on these rakes enough times yet. */
+struct uhid_create_req_compat {
+	__u8 name[128];
+	__u8 phys[64];
+	__u8 uniq[64];
+
+	compat_uptr_t rd_data;
+	__u16 rd_size;
+
+	__u16 bus;
+	__u32 vendor;
+	__u32 product;
+	__u32 version;
+	__u32 country;
+} __attribute__((__packed__));
+
+static int uhid_event_from_user(const char __user *buffer, size_t len,
+				struct uhid_event *event)
+{
+	if (is_compat_task()) {
+		u32 type;
+
+		if (get_user(type, buffer))
+			return -EFAULT;
+
+		if (type == UHID_CREATE) {
+			/*
+			 * This is our messed up request with compat pointer.
+			 * It is largish (more than 256 bytes) so we better
+			 * allocate it from the heap.
+			 */
+			struct uhid_create_req_compat *compat;
+
+			compat = kmalloc(sizeof(*compat), GFP_KERNEL);
+			if (!compat)
+				return -ENOMEM;
+
+			buffer += sizeof(type);
+			len -= sizeof(type);
+			if (copy_from_user(compat, buffer,
+					   min(len, sizeof(*compat)))) {
+				kfree(compat);
+				return -EFAULT;
+			}
+
+			/* Shuffle the data over to proper structure */
+			event->type = type;
+
+			memcpy(event->u.create.name, compat->name,
+				sizeof(compat->name));
+			memcpy(event->u.create.phys, compat->phys,
+				sizeof(compat->phys));
+			memcpy(event->u.create.uniq, compat->uniq,
+				sizeof(compat->uniq));
+
+			event->u.create.rd_data = compat_ptr(compat->rd_data);
+			event->u.create.rd_size = compat->rd_size;
+
+			event->u.create.bus = compat->bus;
+			event->u.create.vendor = compat->vendor;
+			event->u.create.product = compat->product;
+			event->u.create.version = compat->version;
+			event->u.create.country = compat->country;
+
+			kfree(compat);
+			return 0;
+		}
+		/* All others can be copied directly */
+	}
+
+	if (copy_from_user(event, buffer, min(len, sizeof(*event))))
+		return -EFAULT;
+
+	return 0;
+}
+#else
+static int uhid_event_from_user(const char __user *buffer, size_t len,
+				struct uhid_event *event)
+{
+	if (copy_from_user(event, buffer, min(len, sizeof(*event))))
+		return -EFAULT;
+
+	return 0;
+}
+#endif
+
 static int uhid_dev_create(struct uhid_device *uhid,
 			   const struct uhid_event *ev)
 {
@@ -498,10 +587,10 @@ static ssize_t uhid_char_write(struct file *file, const char __user *buffer,
 
 	memset(&uhid->input_buf, 0, sizeof(uhid->input_buf));
 	len = min(count, sizeof(uhid->input_buf));
-	if (copy_from_user(&uhid->input_buf, buffer, len)) {
-		ret = -EFAULT;
+
+	ret = uhid_event_from_user(buffer, len, &uhid->input_buf);
+	if (ret)
 		goto unlock;
-	}
 
 	switch (uhid->input_buf.type) {
 	case UHID_CREATE: