[PATCH 5.10 027/103] USB: xhci: dbc: fix tty registration race

Greg Kroah-Hartman
2021-10-18T13:40:42Z

From: Johan Hovold <johan@kernel.org>

commit 880de403777376e50bdf60def359fa50a722006f upstream.

Make sure to allocate resources before registering the tty device to
avoid having a racing open() and write() fail to enable rx or
dereference a NULL pointer when accessing the uninitialised fifo.

Fixes: dfba2174dc42 ("usb: xhci: Add DbC support in xHCI driver")
Cc: stable@vger.kernel.org # 4.16
Cc: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20211008092547.3996295-4-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/usb/host/xhci-dbgtty.c | 28 +++++++++++++---------------
1 file changed, 13 insertions(+), 15 deletions(-)

--- a/drivers/usb/host/xhci-dbgtty.c
+++ b/drivers/usb/host/xhci-dbgtty.c
@@ -408,40 +408,38 @@ static int xhci_dbc_tty_register_device(
return -EBUSY;

xhci_dbc_tty_init_port(dbc, port);
- tty_dev = tty_port_register_device(&port->port,
- dbc_tty_driver, 0, NULL);
- if (IS_ERR(tty_dev)) {
- ret = PTR_ERR(tty_dev);
- goto register_fail;
- }

ret = kfifo_alloc(&port->write_fifo, DBC_WRITE_BUF_SIZE, GFP_KERNEL);
if (ret)
- goto buf_alloc_fail;
+ goto err_exit_port;

ret = xhci_dbc_alloc_requests(dbc, BULK_IN, &port->read_pool,
dbc_read_complete);
if (ret)
- goto request_fail;
+ goto err_free_fifo;

ret = xhci_dbc_alloc_requests(dbc, BULK_OUT, &port->write_pool,
dbc_write_complete);
if (ret)
- goto request_fail;
+ goto err_free_requests;
+
+ tty_dev = tty_port_register_device(&port->port,
+ dbc_tty_driver, 0, NULL);
+ if (IS_ERR(tty_dev)) {
+ ret = PTR_ERR(tty_dev);
+ goto err_free_requests;
+ }

port->registered = true;

return 0;

-request_fail:
+err_free_requests:
xhci_dbc_free_requests(&port->read_pool);
xhci_dbc_free_requests(&port->write_pool);
+err_free_fifo:
kfifo_free(&port->write_fifo);
-
-buf_alloc_fail:
- tty_unregister_device(dbc_tty_driver, 0);
-
-register_fail:
+err_exit_port:
xhci_dbc_tty_exit_port(port);

dev_err(dbc->dev, "can't register tty port, err %d\n", ret);