Messages in this thread | | | Date | Mon, 27 Mar 2023 13:08:55 +0200 | Subject | Re: [PATCH v7 1/6] usb: Add support for Intel LJCA device | From | Oliver Neukum <> |
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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
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