Re: [PATCH v7 1/6] usb: Add support for Intel LJCA device

Oliver Neukum
2023-03-27T11:09:19Z

On 25.03.23 16:47, Ye Xiang wrote:

Hi,

> +static int ljca_parse(struct ljca_dev *dev, struct ljca_msg *header)
> +{
> + struct ljca_stub *stub;
> +
> + stub = ljca_stub_find(dev, header->type);
> + if (IS_ERR(stub))
> + return PTR_ERR(stub);
> +
> + if (!(header->flags & LJCA_ACK_FLAG)) {
> + ljca_stub_notify(stub, header->cmd, header->data, header->len);
> + return 0;
> + }
> +
> + if (stub->cur_cmd != header->cmd) {
> + dev_err(&dev->intf->dev, "header and stub current command mismatch (%x vs %x)\n",
> + header->cmd, stub->cur_cmd);
> + return -EINVAL;
> + }
> +
> + if (stub->ipacket.ibuf && stub->ipacket.ibuf_len) {

Here you read those values from ipacket.

> + unsigned int newlen;
> +
> + newlen = min_t(unsigned int, header->len, *stub->ipacket.ibuf_len);

Here you read them again.

> +
> + *stub->ipacket.ibuf_len = newlen;
> + memcpy(stub->ipacket.ibuf, header->data, newlen);

And here you read them again. The compiler is free to generate a memory access for
ipacket.ibuf, which may read a new value from RAM. That means here you have a window
in which you can no longer guarantee stub->ipacket.ibuf != NULL,
if you set it to NULL elsewhere.

> + }
> +
> + stub->acked = true;
> + wake_up(&dev->ack_wq);
> +
> + return 0;
> +}
> +
> +static int ljca_stub_write(struct ljca_stub *stub, u8 cmd, const void *obuf, unsigned int obuf_len,
> + void *ibuf, unsigned int *ibuf_len, bool wait_ack, unsigned long timeout)
> +{
> + struct ljca_dev *dev = usb_get_intfdata(stub->intf);
> + u8 flags = LJCA_CMPL_FLAG;
> + struct ljca_msg *header;
> + unsigned int msg_len = sizeof(*header) + obuf_len;
> + int actual;
> + int ret;
> +
> + if (msg_len > LJCA_MAX_PACKET_SIZE)
> + return -EINVAL;
> +
> + if (wait_ack)
> + flags |= LJCA_ACK_FLAG;
> +
> + header = kmalloc(msg_len, GFP_KERNEL);
> + if (!header)
> + return -ENOMEM;
> +
> + header->type = stub->type;
> + header->cmd = cmd;
> + header->flags = flags;
> + header->len = obuf_len;
> +
> + if (obuf)
> + memcpy(header->data, obuf, obuf_len);
> +
> + dev_dbg(&dev->intf->dev, "send: type:%d cmd:%d flags:%d len:%d\n", header->type,
> + header->cmd, header->flags, header->len);
> +
> + usb_autopm_get_interface(dev->intf);
> + if (!dev->started) {
> + kfree(header);
> + ret = -ENODEV;
> + goto error_put;
> + }
> +
> + mutex_lock(&dev->mutex);
> + stub->cur_cmd = cmd;
> + stub->ipacket.ibuf = ibuf;
> + stub->ipacket.ibuf_len = ibuf_len;
> + stub->acked = false;
> + ret = usb_bulk_msg(interface_to_usbdev(dev->intf),
> + usb_sndbulkpipe(interface_to_usbdev(dev->intf), dev->out_ep), header,
> + msg_len, &actual, LJCA_USB_WRITE_TIMEOUT_MS);
> + kfree(header);
> + if (ret) {
> + dev_err(&dev->intf->dev, "bridge write failed ret:%d\n", ret);
> + goto error_unlock;
> + }
> +
> + if (actual != msg_len) {
> + dev_err(&dev->intf->dev, "bridge write length mismatch (%d vs %d)\n", msg_len,
> + actual);
> + ret = -EINVAL;
> + goto error_unlock;
> + }
> +
> + if (wait_ack) {
> + ret = wait_event_timeout(dev->ack_wq, stub->acked, msecs_to_jiffies(timeout));
> + if (!ret) {
> + dev_err(&dev->intf->dev, "acked wait timeout\n");
> + ret = -ETIMEDOUT;
> + goto error_unlock;
> + }
> + }
> +
> + ret = 0;
> +error_unlock:
> + stub->ipacket.ibuf = NULL;
> + stub->ipacket.ibuf_len = NULL;

And here you set stub->ipacket.ibuf to NULL.
If you do that and want consistency, you'll need to use READ_ONCE
and a local variable if you read this in interrupt.

> + mutex_unlock(&dev->mutex);
> +error_put:
> + usb_autopm_put_interface(dev->intf);
> +
> + return ret;
> +}
> +

HTH,
Oliver