Bluetooth: vhci: Fix info leak in force_devcd_write()

There are a number of bugs here:

1) If "count" is less than sizeof(dump_data.data) then it copies
uninitialized data.
2) If simple_write_to_buffer() returns -EFAULT then we run into a
problem "ret < count" comparison. "count" is an unsigned long so the
comparison is type promoted to unsigned long and the negative returns
become high positive values. That also results in copying
uninitialized data.
3) If "*ppos" is non-zero then the first part of the dump_data
buffer is uninitialized. Using copy_from_user() instead of
simple_write_to_buffer() is more appropriate here.

Fixes: d5d5df6da0aa ("Bluetooth: Add vhci devcoredump support")
Signed-off-by: Dan Carpenter <[e-mail]>
Signed-off-by: Luiz Augusto von Dentz <[e-mail]>

drivers/bluetooth/hci_vhci.c

···
 	struct hci_dev *hdev = data->hdev;
 	struct sk_buff *skb = NULL;
 	struct devcoredump_test_data dump_data;
+	size_t data_size;
 	int ret;
 
-	ret = simple_write_to_buffer(&dump_data, sizeof(dump_data), ppos,
-				     user_buf, count);
-	if (ret < count)
-		return ret;
+	if (count < offsetof(struct devcoredump_test_data, data) ||
+	    count > sizeof(dump_data))
+		return -EINVAL;
 
-	skb = alloc_skb(sizeof(dump_data.data), GFP_ATOMIC);
+	if (copy_from_user(&dump_data, user_buf, count))
+		return -EFAULT;
+
+	data_size = count - offsetof(struct devcoredump_test_data, data);
+	skb = alloc_skb(data_size, GFP_ATOMIC);
 	if (!skb)
 		return -ENOMEM;
-	skb_put_data(skb, &dump_data.data, sizeof(dump_data.data));
+	skb_put_data(skb, &dump_data.data, data_size);
 
 	hci_devcd_register(hdev, vhci_coredump, vhci_coredump_hdr, NULL);